diff options
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/Kconfig | 46 | ||||
| -rw-r--r-- | kernel/rcu/Kconfig.debug | 4 | ||||
| -rw-r--r-- | kernel/rcu/rcu.h | 7 | ||||
| -rw-r--r-- | kernel/rcu/rcuperf.c | 5 | ||||
| -rw-r--r-- | kernel/rcu/rcutorture.c | 155 | ||||
| -rw-r--r-- | kernel/rcu/tasks.h | 1193 | ||||
| -rw-r--r-- | kernel/rcu/tree.c | 138 | ||||
| -rw-r--r-- | kernel/rcu/tree.h | 2 | ||||
| -rw-r--r-- | kernel/rcu/tree_exp.h | 31 | ||||
| -rw-r--r-- | kernel/rcu/tree_plugin.h | 67 | ||||
| -rw-r--r-- | kernel/rcu/tree_stall.h | 106 | ||||
| -rw-r--r-- | kernel/rcu/update.c | 380 |
12 files changed, 1669 insertions, 465 deletions
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index 1cc940fef17c..0ebe15a84985 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -70,13 +70,37 @@ config TREE_SRCU help This option selects the full-fledged version of SRCU. +config TASKS_RCU_GENERIC + def_bool TASKS_RCU || TASKS_RUDE_RCU || TASKS_TRACE_RCU + select SRCU + help + This option enables generic infrastructure code supporting + task-based RCU implementations. Not for manual selection. + config TASKS_RCU def_bool PREEMPTION - select SRCU help This option enables a task-based RCU implementation that uses only voluntary context switch (not preemption!), idle, and - user-mode execution as quiescent states. + user-mode execution as quiescent states. Not for manual selection. + +config TASKS_RUDE_RCU + def_bool 0 + help + This option enables a task-based RCU implementation that uses + only context switch (including preemption) and user-mode + execution as quiescent states. It forces IPIs and context + switches on all online CPUs, including idle ones, so use + with caution. + +config TASKS_TRACE_RCU + def_bool 0 + help + This option enables a task-based RCU implementation that uses + explicit rcu_read_lock_trace() read-side markers, and allows + these readers to appear in the idle loop as well as on the CPU + hotplug code paths. It can force IPIs on online CPUs, including + idle ones, so use with caution. config RCU_STALL_COMMON def_bool TREE_RCU @@ -210,4 +234,22 @@ config RCU_NOCB_CPU Say Y here if you want to help to debug reduced OS jitter. Say N here if you are unsure. +config TASKS_TRACE_RCU_READ_MB + bool "Tasks Trace RCU readers use memory barriers in user and idle" + depends on RCU_EXPERT + default PREEMPT_RT || NR_CPUS < 8 + help + Use this option to further reduce the number of IPIs sent + to CPUs executing in userspace or idle during tasks trace + RCU grace periods. Given that a reasonable setting of + the rcupdate.rcu_task_ipi_delay kernel boot parameter + eliminates such IPIs for many workloads, proper setting + of this Kconfig option is important mostly for aggressive + real-time installations and for battery-powered devices, + hence the default chosen above. + + Say Y here if you hate IPIs. + Say N here if you hate read-side memory barriers. + Take the default if you are unsure. + endmenu # "RCU Subsystem" diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug index 4aa02eee8f6c..452feae8de20 100644 --- a/kernel/rcu/Kconfig.debug +++ b/kernel/rcu/Kconfig.debug @@ -29,6 +29,8 @@ config RCU_PERF_TEST select TORTURE_TEST select SRCU select TASKS_RCU + select TASKS_RUDE_RCU + select TASKS_TRACE_RCU default n help This option provides a kernel module that runs performance @@ -46,6 +48,8 @@ config RCU_TORTURE_TEST select TORTURE_TEST select SRCU select TASKS_RCU + select TASKS_RUDE_RCU + select TASKS_TRACE_RCU default n help This option provides a kernel module that runs torture tests diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index 00ddc92c5774..cf66a3ccd757 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -431,6 +431,7 @@ bool rcu_gp_is_expedited(void); /* Internal RCU use. */ void rcu_expedite_gp(void); void rcu_unexpedite_gp(void); void rcupdate_announce_bootup_oddness(void); +void show_rcu_tasks_gp_kthreads(void); void rcu_request_urgent_qs_task(struct task_struct *t); #endif /* #else #ifdef CONFIG_TINY_RCU */ @@ -441,6 +442,8 @@ void rcu_request_urgent_qs_task(struct task_struct *t); enum rcutorture_type { RCU_FLAVOR, RCU_TASKS_FLAVOR, + RCU_TASKS_RUDE_FLAVOR, + RCU_TASKS_TRACING_FLAVOR, RCU_TRIVIAL_FLAVOR, SRCU_FLAVOR, INVALID_RCU_FLAVOR @@ -454,6 +457,7 @@ void do_trace_rcu_torture_read(const char *rcutorturename, unsigned long secs, unsigned long c_old, unsigned long c); +void rcu_gp_set_torture_wait(int duration); #else static inline void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags, unsigned long *gp_seq) @@ -471,6 +475,7 @@ void do_trace_rcu_torture_read(const char *rcutorturename, #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \ do { } while (0) #endif +static inline void rcu_gp_set_torture_wait(int duration) { } #endif #if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST) @@ -498,6 +503,7 @@ void srcutorture_get_gp_data(enum rcutorture_type test_type, #endif #ifdef CONFIG_TINY_RCU +static inline bool rcu_dynticks_zero_in_eqs(int cpu, int *vp) { return false; } static inline unsigned long rcu_get_gp_seq(void) { return 0; } static inline unsigned long rcu_exp_batches_completed(void) { return 0; } static inline unsigned long @@ -507,6 +513,7 @@ static inline void show_rcu_gp_kthreads(void) { } static inline int rcu_get_gp_kthreads_prio(void) { return 0; } static inline void rcu_fwd_progress_check(unsigned long j) { } #else /* #ifdef CONFIG_TINY_RCU */ +bool rcu_dynticks_zero_in_eqs(int cpu, int *vp); unsigned long rcu_get_gp_seq(void); unsigned long rcu_exp_batches_completed(void); unsigned long srcu_batches_completed(struct srcu_struct *sp); diff --git a/kernel/rcu/rcuperf.c b/kernel/rcu/rcuperf.c index a4a8d097d84d..16dd1e6b7c09 100644 --- a/kernel/rcu/rcuperf.c +++ b/kernel/rcu/rcuperf.c @@ -88,6 +88,7 @@ torture_param(bool, shutdown, RCUPERF_SHUTDOWN, torture_param(int, verbose, 1, "Enable verbose debugging printk()s"); torture_param(int, writer_holdoff, 0, "Holdoff (us) between GPs, zero to disable"); torture_param(int, kfree_rcu_test, 0, "Do we run a kfree_rcu() perf test?"); +torture_param(int, kfree_mult, 1, "Multiple of kfree_obj size to allocate."); static char *perf_type = "rcu"; module_param(perf_type, charp, 0444); @@ -635,7 +636,7 @@ kfree_perf_thread(void *arg) } for (i = 0; i < kfree_alloc_num; i++) { - alloc_ptr = kmalloc(sizeof(struct kfree_obj), GFP_KERNEL); + alloc_ptr = kmalloc(kfree_mult * sizeof(struct kfree_obj), GFP_KERNEL); if (!alloc_ptr) return -ENOMEM; @@ -722,6 +723,8 @@ kfree_perf_init(void) schedule_timeout_uninterruptible(1); } + pr_alert("kfree object size=%lu\n", kfree_mult * sizeof(struct kfree_obj)); + kfree_reader_tasks = kcalloc(kfree_nrealthreads, sizeof(kfree_reader_tasks[0]), GFP_KERNEL); if (kfree_reader_tasks == NULL) { diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index 5453bd557f43..efb792e13fca 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -20,7 +20,7 @@ #include <linux/err.h> #include <linux/spinlock.h> #include <linux/smp.h> -#include <linux/rcupdate.h> +#include <linux/rcupdate_wait.h> #include <linux/interrupt.h> #include <linux/sched/signal.h> #include <uapi/linux/sched/types.h> @@ -45,12 +45,25 @@ #include <linux/sched/sysctl.h> #include <linux/oom.h> #include <linux/tick.h> +#include <linux/rcupdate_trace.h> #include "rcu.h" MODULE_LICENSE("GPL"); MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.ibm.com> and Josh Triplett <josh@joshtriplett.org>"); +#ifndef data_race +#define data_race(expr) \ + ({ \ + expr; \ + }) +#endif +#ifndef ASSERT_EXCLUSIVE_WRITER +#define ASSERT_EXCLUSIVE_WRITER(var) do { } while (0) +#endif +#ifndef ASSERT_EXCLUSIVE_ACCESS +#define ASSERT_EXCLUSIVE_ACCESS(var) do { } while (0) +#endif /* Bits for ->extendables field, extendables param, and related definitions. */ #define RCUTORTURE_RDR_SHIFT 8 /* Put SRCU index in upper bits. */ @@ -102,6 +115,9 @@ torture_param(int, stall_cpu, 0, "Stall duration (s), zero to disable."); torture_param(int, stall_cpu_holdoff, 10, "Time to wait before starting stall (s)."); torture_param(int, stall_cpu_irqsoff, 0, "Disable interrupts while stalling."); +torture_param(int, stall_cpu_block, 0, "Sleep while stalling."); +torture_param(int, stall_gp_kthread, 0, + "Grace-period kthread stall duration (s)."); torture_param(int, stat_interval, 60, "Number of seconds between stats printk()s"); torture_param(int, stutter, 5, "Number of seconds to run/halt test"); @@ -665,6 +681,11 @@ static void rcu_tasks_torture_deferred_free(struct rcu_torture *p) call_rcu_tasks(&p->rtort_rcu, rcu_torture_cb); } +static void synchronize_rcu_mult_test(void) +{ + synchronize_rcu_mult(call_rcu_tasks, call_rcu); +} + static struct rcu_torture_ops tasks_ops = { .ttype = RCU_TASKS_FLAVOR, .init = rcu_sync_torture_init, @@ -674,7 +695,7 @@ static struct rcu_torture_ops tasks_ops = { .get_gp_seq = rcu_no_completed, .deferred_free = rcu_tasks_torture_deferred_free, .sync = synchronize_rcu_tasks, - .exp_sync = synchronize_rcu_tasks, + .exp_sync = synchronize_rcu_mult_test, .call = call_rcu_tasks, .cb_barrier = rcu_barrier_tasks, .fqs = NULL, @@ -725,6 +746,72 @@ static struct rcu_torture_ops trivial_ops = { .name = "trivial" }; +/* + * Definitions for rude RCU-tasks torture testing. + */ + +static void rcu_tasks_rude_torture_deferred_free(struct rcu_torture *p) +{ + call_rcu_tasks_rude(&p->rtort_rcu, rcu_torture_cb); +} + +static struct rcu_torture_ops tasks_rude_ops = { + .ttype = RCU_TASKS_RUDE_FLAVOR, + .init = rcu_sync_torture_init, + .readlock = rcu_torture_read_lock_trivial, + .read_delay = rcu_read_delay, /* just reuse rcu's version. */ + .readunlock = rcu_torture_read_unlock_trivial, + .get_gp_seq = rcu_no_completed, + .deferred_free = rcu_tasks_rude_torture_deferred_free, + .sync = synchronize_rcu_tasks_rude, + .exp_sync = synchronize_rcu_tasks_rude, + .call = call_rcu_tasks_rude, + .cb_barrier = rcu_barrier_tasks_rude, + .fqs = NULL, + .stats = NULL, + .irq_capable = 1, + .name = "tasks-rude" +}; + +/* + * Definitions for tracing RCU-tasks torture testing. + */ + +static int tasks_tracing_torture_read_lock(void) +{ + rcu_read_lock_trace(); + return 0; +} + +static void tasks_tracing_torture_read_unlock(int idx) +{ + rcu_read_unlock_trace(); +} + +static void rcu_tasks_tracing_torture_deferred_free(struct rcu_torture *p) +{ + call_rcu_tasks_trace(&p->rtort_rcu, rcu_torture_cb); +} + +static struct rcu_torture_ops tasks_tracing_ops = { + .ttype = RCU_TASKS_TRACING_FLAVOR, + .init = rcu_sync_torture_init, + .readlock = tasks_tracing_torture_read_lock, + .read_delay = srcu_read_delay, /* just reuse srcu's version. */ + .readunlock = tasks_tracing_torture_read_unlock, + .get_gp_seq = rcu_no_completed, + .deferred_free = rcu_tasks_tracing_torture_deferred_free, + .sync = synchronize_rcu_tasks_trace, + .exp_sync = synchronize_rcu_tasks_trace, + .call = call_rcu_tasks_trace, + .cb_barrier = rcu_barrier_tasks_trace, + .fqs = NULL, + .stats = NULL, + .irq_capable = 1, + .slow_gps = 1, + .name = "tasks-tracing" +}; + static unsigned long rcutorture_seq_diff(unsigned long new, unsigned long old) { if (!cur_ops->gp_diff) @@ -734,7 +821,7 @@ static unsigned long rcutorture_seq_diff(unsigned long new, unsigned long old) static bool __maybe_unused torturing_tasks(void) { - return cur_ops == &tasks_ops; + return cur_ops == &tasks_ops || cur_ops == &tasks_rude_ops; } /* @@ -833,7 +920,7 @@ static int rcu_torture_boost(void *arg) /* Wait for the next test interval. */ oldstarttime = boost_starttime; - while (ULONG_CMP_LT(jiffies, oldstarttime)) { + while (time_before(jiffies, oldstarttime)) { schedule_timeout_interruptible(oldstarttime - jiffies); stutter_wait("rcu_torture_boost"); if (torture_must_stop()) @@ -843,7 +930,7 @@ static int rcu_torture_boost(void *arg) /* Do one boost-test interval. */ endtime = oldstarttime + test_boost_duration * HZ; call_rcu_time = jiffies; - while (ULONG_CMP_LT(jiffies, endtime)) { + while (time_before(jiffies, endtime)) { /* If we don't have a callback in flight, post one. */ if (!smp_load_acquire(&rbi.inflight)) { /* RCU core before ->inflight = 1. */ @@ -914,7 +1001,7 @@ rcu_torture_fqs(void *arg) VERBOSE_TOROUT_STRING("rcu_torture_fqs task started"); do { fqs_resume_time = jiffies + fqs_stutter * HZ; - while (ULONG_CMP_LT(jiffies, fqs_resume_time) && + while (time_before(jiffies, fqs_resume_time) && !kthread_should_stop()) { schedule_timeout_interruptible(1); } @@ -1147,6 +1234,7 @@ static void rcutorture_one_extend(int *readstate, int newstate, struct torture_random_state *trsp, struct rt_read_seg *rtrsp) { + unsigned long flags; int idxnew = -1; int idxold = *readstate; int statesnew = ~*readstate & newstate; @@ -1181,8 +1269,15 @@ static void rcutorture_one_extend(int *readstate, int newstate, rcu_read_unlock_bh(); if (statesold & RCUTORTURE_RDR_SCHED) rcu_read_unlock_sched(); - if (statesold & RCUTORTURE_RDR_RCU) + if (statesold & RCUTORTURE_RDR_RCU) { + bool lockit = !statesnew && !(torture_random(trsp) & 0xffff); + + if (lockit) + raw_spin_lock_irqsave(¤t->pi_lock, flags); cur_ops->readunlock(idxold >> RCUTORTURE_RDR_SHIFT); + if (lockit) + raw_spin_unlock_irqrestore(¤t->pi_lock, flags); + } /* Delay if neither beginning nor end and there was a change. */ if ((statesnew || statesold) && *readstate && newstate) @@ -1283,6 +1378,7 @@ static bool rcu_torture_one_read(struct torture_random_state *trsp) rcu_read_lock_bh_held() || rcu_read_lock_sched_held() || srcu_read_lock_held(srcu_ctlp) || + rcu_read_lock_trace_held() || torturing_tasks()); if (p == NULL) { /* Wait for rcu_torture_writer to get underway */ @@ -1444,9 +1540,9 @@ rcu_torture_stats_print(void) atomic_long_read(&n_rcu_torture_timers)); torture_onoff_stats(); pr_cont("barrier: %ld/%ld:%ld\n", - n_barrier_successes, - n_barrier_attempts, - n_rcu_torture_barrier_error); + data_race(n_barrier_successes), + data_race(n_barrier_attempts), + data_race(n_rcu_torture_barrier_error)); pr_alert("%s%s ", torture_type, TORTURE_FLAG); if (atomic_read(&n_rcu_torture_mberror) || @@ -1536,6 +1632,7 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, const char *tag) "test_boost=%d/%d test_boost_interval=%d " "test_boost_duration=%d shutdown_secs=%d " "stall_cpu=%d stall_cpu_holdoff=%d stall_cpu_irqsoff=%d " + "stall_cpu_block=%d " "n_barrier_cbs=%d " "onoff_interval=%d onoff_holdoff=%d\n", torture_type, tag, nrealreaders, nfakewriters, @@ -1544,6 +1641,7 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, const char *tag) test_boost, cur_ops->can_boost, test_boost_interval, test_boost_duration, shutdown_secs, stall_cpu, stall_cpu_holdoff, stall_cpu_irqsoff, + stall_cpu_block, n_barrier_cbs, onoff_interval, onoff_holdoff); } @@ -1599,6 +1697,7 @@ static int rcutorture_booster_init(unsigned int cpu) */ static int rcu_torture_stall(void *args) { + int idx; unsigned long stop_at; VERBOSE_TOROUT_STRING("rcu_torture_stall task started"); @@ -1607,26 +1706,37 @@ static int rcu_torture_stall(void *args) schedule_timeout_interruptible(stall_cpu_holdoff * HZ); VERBOSE_TOROUT_STRING("rcu_torture_stall end holdoff"); } - if (!kthread_should_stop()) { + if (!kthread_should_stop() && stall_gp_kthread > 0) { + VERBOSE_TOROUT_STRING("rcu_torture_stall begin GP stall"); + rcu_gp_set_torture_wait(stall_gp_kthread * HZ); + for (idx = 0; idx < stall_gp_kthread + 2; idx++) { + if (kthread_should_stop()) + break; + schedule_timeout_uninterruptible(HZ); + } + } + if (!kthread_should_stop() && stall_cpu > 0) { + VERBOSE_TOROUT_STRING("rcu_torture_stall begin CPU stall"); stop_at = ktime_get_seconds() + stall_cpu; /* RCU CPU stall is expected behavior in following code. */ - rcu_read_lock(); + idx = cur_ops->readlock(); if (stall_cpu_irqsoff) local_irq_disable(); - else + else if (!stall_cpu_block) preempt_disable(); pr_alert("rcu_torture_stall start on CPU %d.\n", - smp_processor_id()); + raw_smp_processor_id()); while (ULONG_CMP_LT((unsigned long)ktime_get_seconds(), stop_at)) - continue; /* Induce RCU CPU stall warning. */ + if (stall_cpu_block) + schedule_timeout_uninterruptible(HZ); if (stall_cpu_irqsoff) local_irq_enable(); - else + else if (!stall_cpu_block) preempt_enable(); - rcu_read_unlock(); - pr_alert("rcu_torture_stall end.\n"); + cur_ops->readunlock(idx); } + pr_alert("rcu_torture_stall end.\n"); torture_shutdown_absorb("rcu_torture_stall"); while (!kthread_should_stop()) schedule_timeout_interruptible(10 * HZ); @@ -1636,7 +1746,7 @@ static int rcu_torture_stall(void *args) /* Spawn CPU-stall kthread, if stall_cpu specified. */ static int __init rcu_torture_stall_init(void) { - if (stall_cpu <= 0) + if (stall_cpu <= 0 && stall_gp_kthread <= 0) return 0; return torture_create_kthread(rcu_torture_stall, NULL, stall_task); } @@ -1692,8 +1802,8 @@ struct rcu_fwd { unsigned long rcu_launder_gp_seq_start; }; -struct rcu_fwd *rcu_fwds; -bool rcu_fwd_emergency_stop; +static struct rcu_fwd *rcu_fwds; +static bool rcu_fwd_emergency_stop; static void rcu_torture_fwd_cb_hist(struct rcu_fwd *rfp) { @@ -2400,7 +2510,8 @@ rcu_torture_init(void) int firsterr = 0; static struct rcu_torture_ops *torture_ops[] = { &rcu_ops, &rcu_busted_ops, &srcu_ops, &srcud_ops, - &busted_srcud_ops, &tasks_ops, &trivial_ops, + &busted_srcud_ops, &tasks_ops, &tasks_rude_ops, + &tasks_tracing_ops, &trivial_ops, }; if (!torture_init_begin(torture_type, verbose)) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h new file mode 100644 index 000000000000..ce23f6cc5043 --- /dev/null +++ b/kernel/rcu/tasks.h @@ -0,0 +1,1193 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/* + * Task-based RCU implementations. + * + * Copyright (C) 2020 Paul E. McKenney + */ + +#ifdef CONFIG_TASKS_RCU_GENERIC + +//////////////////////////////////////////////////////////////////////// +// +// Generic data structures. + +struct rcu_tasks; +typedef void (*rcu_tasks_gp_func_t)(struct rcu_tasks *rtp); +typedef void (*pregp_func_t)(void); +typedef void (*pertask_func_t)(struct task_struct *t, struct list_head *hop); +typedef void (*postscan_func_t)(struct list_head *hop); +typedef void (*holdouts_func_t)(struct list_head *hop, bool ndrpt, bool *frptp); +typedef void (*postgp_func_t)(struct rcu_tasks *rtp); + +/** + * Definition for a Tasks-RCU-like mechanism. + * @cbs_head: Head of callback list. + * @cbs_tail: Tail pointer for callback list. + * @cbs_wq: Wait queue allowning new callback to get kthread's attention. + * @cbs_lock: Lock protecting callback list. + * @kthread_ptr: This flavor's grace-period/callback-invocation kthread. + * @gp_func: This flavor's grace-period-wait function. + * @gp_state: Grace period's most recent state transition (debugging). + * @gp_jiffies: Time of last @gp_state transition. + * @gp_start: Most recent grace-period start in jiffies. + * @n_gps: Number of grace periods completed since boot. + * @n_ipis: Number of IPIs sent to encourage grace periods to end. + * @n_ipis_fails: Number of IPI-send failures. + * @pregp_func: This flavor's pre-grace-period function (optional). + * @pertask_func: This flavor's per-task scan function (optional). + * @postscan_func: This flavor's post-task scan function (optional). + * @holdout_func: This flavor's holdout-list scan function (optional). + * @postgp_func: This flavor's post-grace-period function (optional). + * @call_func: This flavor's call_rcu()-equivalent function. + * @name: This flavor's textual name. + * @kname: This flavor's kthread name. + */ +struct rcu_tasks { + struct rcu_head *cbs_head; + struct rcu_head **cbs_tail; + struct wait_queue_head cbs_wq; + raw_spinlock_t cbs_lock; + int gp_state; + unsigned long gp_jiffies; + unsigned long gp_start; + unsigned long n_gps; + unsigned long n_ipis; + unsigned long n_ipis_fails; + struct task_struct *kthread_ptr; + rcu_tasks_gp_func_t gp_func; + pregp_func_t pregp_func; + pertask_func_t pertask_func; + postscan_func_t postscan_func; + holdouts_func_t holdouts_func; + postgp_func_t postgp_func; + call_rcu_func_t call_func; + char *name; + char *kname; +}; + +#define DEFINE_RCU_TASKS(rt_name, gp, call, n) \ +static struct rcu_tasks rt_name = \ +{ \ + .cbs_tail = &rt_name.cbs_head, \ + .cbs_wq = __WAIT_QUEUE_HEAD_INITIALIZER(rt_name.cbs_wq), \ + .cbs_lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name.cbs_lock), \ + .gp_func = gp, \ + .call_func = call, \ + .name = n, \ + .kname = #rt_name, \ +} + +/* Track exiting tasks in order to allow them to be waited for. */ +DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu); + +/* Avoid IPIing CPUs early in the grace period. */ +#define RCU_TASK_IPI_DELAY (HZ / 2) +static int rcu_task_ipi_delay __read_mostly = RCU_TASK_IPI_DELAY; +module_param(rcu_task_ipi_delay, int, 0644); + +/* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */ +#define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10) +static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT; +module_param(rcu_task_stall_timeout, int, 0644); + +/* RCU tasks grace-period state for debugging. */ +#define RTGS_INIT 0 +#define RTGS_WAIT_WAIT_CBS 1 +#define RTGS_WAIT_GP 2 +#define RTGS_PRE_WAIT_GP 3 +#define RTGS_SCAN_TASKLIST 4 +#define RTGS_POST_SCAN_TASKLIST 5 +#define RTGS_WAIT_SCAN_HOLDOUTS 6 +#define RTGS_SCAN_HOLDOUTS 7 +#define RTGS_POST_GP 8 +#define RTGS_WAIT_READERS 9 +#define RTGS_INVOKE_CBS 10 +#define RTGS_WAIT_CBS 11 +static const char * const rcu_tasks_gp_state_names[] = { + "RTGS_INIT", + "RTGS_WAIT_WAIT_CBS", + "RTGS_WAIT_GP", + "RTGS_PRE_WAIT_GP", + "RTGS_SCAN_TASKLIST", + "RTGS_POST_SCAN_TASKLIST", + "RTGS_WAIT_SCAN_HOLDOUTS", + "RTGS_SCAN_HOLDOUTS", + "RTGS_POST_GP", + "RTGS_WAIT_READERS", + "RTGS_INVOKE_CBS", + "RTGS_WAIT_CBS", +}; + +//////////////////////////////////////////////////////////////////////// +// +// Generic code. + +/* Record grace-period phase and time. */ +static void set_tasks_gp_state(struct rcu_tasks *rtp, int newstate) +{ + rtp->gp_state = newstate; + rtp->gp_jiffies = jiffies; +} + +/* Return state name. */ +static const char *tasks_gp_state_getname(struct rcu_tasks *rtp) +{ + int i = data_race(rtp->gp_state); // Let KCSAN detect update races + int j = READ_ONCE(i); // Prevent the compiler from reading twice + + if (j >= ARRAY_SIZE(rcu_tasks_gp_state_names)) + return "???"; + return rcu_tasks_gp_state_names[j]; +} + +// Enqueue a callback for the specified flavor of Tasks RCU. +static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func, + struct rcu_tasks *rtp) +{ + unsigned long flags; + bool needwake; + + rhp->next = NULL; + rhp->func = func; + raw_spin_lock_irqsave(&rtp->cbs_lock, flags); + needwake = !rtp->cbs_head; + WRITE_ONCE(*rtp->cbs_tail, rhp); + rtp->cbs_tail = &rhp->next; + raw_spin_unlock_irqrestore(&rtp->cbs_lock, flags); + /* We can't create the thread unless interrupts are enabled. */ + if (needwake && READ_ONCE(rtp->kthread_ptr)) + wake_up(&rtp->cbs_wq); +} + +// Wait for a grace period for the specified flavor of Tasks RCU. +static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp) +{ + /* Complain if the scheduler has not started. */ + RCU_LOCKDEP_WARN(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE, + "synchronize_rcu_tasks called too soon"); + + /* Wait for the grace period. */ + wait_rcu_gp(rtp->call_func); +} + +/* RCU-tasks kthread that detects grace periods and invokes callbacks. */ +static int __noreturn rcu_tasks_kthread(void *arg) +{ + unsigned long flags; + struct rcu_head *list; + struct rcu_head *next; + struct rcu_tasks *rtp = arg; + + /* Run on housekeeping CPUs by default. Sysadm can move if desired. */ + housekeeping_affine(current, HK_FLAG_RCU); + WRITE_ONCE(rtp->kthread_ptr, current); // Let GPs start! + + /* + * Each pass through the following loop makes one check for + * newly arrived callbacks, and, if there are some, waits for + * one RCU-tasks grace period and then invokes the callbacks. + * This loop is terminated by the system going down. ;-) + */ + for (;;) { + + /* Pick up any new callbacks. */ + raw_spin_lock_irqsave(&rtp->cbs_lock, flags); + smp_mb__after_spinlock(); // Order updates vs. GP. + list = rtp->cbs_head; + rtp->cbs_head = NULL; + rtp->cbs_tail = &rtp->cbs_head; + raw_spin_unlock_irqrestore(&rtp->cbs_lock, flags); + + /* If there were none, wait a bit and start over. */ + if (!list) { + wait_event_interruptible(rtp->cbs_wq, + READ_ONCE(rtp->cbs_head)); + if (!rtp->cbs_head) { + WARN_ON(signal_pending(current)); + set_tasks_gp_state(rtp, RTGS_WAIT_WAIT_CBS); + schedule_timeout_interruptible(HZ/10); + } + continue; + } + + // Wait for one grace period. + set_tasks_gp_state(rtp, RTGS_WAIT_GP); + rtp->gp_start = jiffies; + rtp->gp_func(rtp); + rtp->n_gps++; + + /* Invoke the callbacks. */ + set_tasks_gp_state(rtp, RTGS_INVOKE_CBS); + while (list) { + next = list->next; + local_bh_disable(); + list->func(list); + local_bh_enable(); + list = next; + cond_resched(); + } + /* Paranoid sleep to keep this from entering a tight loop */ + schedule_timeout_uninterruptible(HZ/10); + + set_tasks_gp_state(rtp, RTGS_WAIT_CBS); + } +} + +/* Spawn RCU-tasks grace-period kthread, e.g., at core_initcall() time. */ +static void __init rcu_spawn_tasks_kthread_generic(struct rcu_tasks *rtp) +{ + struct task_struct *t; + + t = kthread_run(rcu_tasks_kthread, rtp, "%s_kthread", rtp->kname); + if (WARN_ONCE(IS_ERR(t), "%s: Could not start %s grace-period kthread, OOM is now expected behavior\n", __func__, rtp->name)) + return; + smp_mb(); /* Ensure others see full kthread. */ +} + +#ifndef CONFIG_TINY_RCU + +/* + * Print any non-default Tasks RCU settings. + */ +static void __init rcu_tasks_bootup_oddness(void) +{ +#if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU) + if (rcu_task_stall_timeout != RCU_TASK_STALL_TIMEOUT) + pr_info("\tTasks-RCU CPU stall warnings timeout set to %d (rcu_task_stall_timeout).\n", rcu_task_stall_timeout); +#endif /* #ifdef CONFIG_TASKS_RCU */ +#ifdef CONFIG_TASKS_RCU + pr_info("\tTrampoline variant of Tasks RCU enabled.\n"); +#endif /* #ifdef CONFIG_TASKS_RCU */ +#ifdef CONFIG_TASKS_RUDE_RCU + pr_info("\tRude variant of Tasks RCU enabled.\n"); +#endif /* #ifdef CONFIG_TASKS_RUDE_RCU */ +#ifdef CONFIG_TASKS_TRACE_RCU + pr_info("\tTracing variant of Tasks RCU enabled.\n"); +#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */ +} + +#endif /* #ifndef CONFIG_TINY_RCU */ + +/* Dump out rcutorture-relevant state common to all RCU-tasks flavors. */ +static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s) +{ + pr_info("%s: %s(%d) since %lu g:%lu i:%lu/%lu %c%c %s\n", + rtp->kname, + tasks_gp_state_getname(rtp), data_race(rtp->gp_state), + jiffies - data_race(rtp->gp_jiffies), + data_race(rtp->n_gps), + data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis), + ".k"[!!data_race(rtp->kthread_ptr)], + ".C"[!!data_race(rtp->cbs_head)], + s); +} + +static void exit_tasks_rcu_finish_trace(struct task_struct *t); + +#if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU) + +//////////////////////////////////////////////////////////////////////// +// +// Shared code between task-list-scanning variants of Tasks RCU. + +/* Wait for one RCU-tasks grace period. */ +static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) +{ + struct task_struct *g, *t; + unsigned long lastreport; + LIST_HEAD(holdouts); + int fract; + + set_tasks_gp_state(rtp, RTGS_PRE_WAIT_GP); + rtp->pregp_func(); + + /* + * There were callbacks, so we need to wait for an RCU-tasks + * grace period. Start off by scanning the task list for tasks + * that are not already voluntarily blocked. Mark these tasks + * and make a list of them in holdouts. + */ + set_tasks_gp_state(rtp, RTGS_SCAN_TASKLIST); + rcu_read_lock(); + for_each_process_thread(g, t) + rtp->pertask_func(t, &holdouts); + rcu_read_unlock(); + + set_tasks_gp_state(rtp, RTGS_POST_SCAN_TASKLIST); + rtp->postscan_func(&holdouts); + + /* + * Each pass through the following loop scans the list of holdout + * tasks, removing any that are no longer holdouts. When the list + * is empty, we are done. + */ + lastreport = jiffies; + + /* Start off with HZ/10 wait and slowly back off to 1 HZ wait. */ + fract = 10; + + for (;;) { + bool firstreport; + bool needreport; + int rtst; + + if (list_empty(&holdouts)) + break; + + /* Slowly back off waiting for holdouts */ + set_tasks_gp_state(rtp, RTGS_WAIT_SCAN_HOLDOUTS); + schedule_timeout_interruptible(HZ/fract); + + if (fract > 1) + fract--; + + rtst = READ_ONCE(rcu_task_stall_timeout); + needreport = rtst > 0 && time_after(jiffies, lastreport + rtst); + if (needreport) + lastreport = jiffies; + firstreport = true; + WARN_ON(signal_pending(current)); + set_tasks_gp_state(rtp, RTGS_SCAN_HOLDOUTS); + rtp->holdouts_func(&holdouts, needreport, &firstreport); + } + + set_tasks_gp_state(rtp, RTGS_POST_GP); + rtp->postgp_func(rtp); +} + +#endif /* #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU) */ + +#ifdef CONFIG_TASKS_RCU + +//////////////////////////////////////////////////////////////////////// +// +// Simple variant of RCU whose quiescent states are voluntary context +// switch, cond_resched_rcu_qs(), user-space execution, and idle. +// As such, grace periods can take one good long time. There are no +// read-side primitives similar to rcu_read_lock() and rcu_read_unlock() +// because this implementation is intended to get the system into a safe +// state for some of the manipulations involved in tracing and the like. +// Finally, this implementation does not support high call_rcu_tasks() +// rates from multiple CPUs. If this is required, per-CPU callback lists +// will be needed. + +/* Pre-grace-period preparation. */ +static void rcu_tasks_pregp_step(void) +{ + /* + * Wait for all pre-existing t->on_rq and t->nvcsw transitions + * to complete. Invoking synchronize_rcu() suffices because all + * these transitions occur with interrupts disabled. Without this + * synchronize_rcu(), a read-side critical section that started + * before the grace period might be incorrectly seen as having + * started after the grace period. + * + * This synchronize_rcu() also dispenses with the need for a + * memory barrier on the first store to t->rcu_tasks_holdout, + * as it forces the store to happen after the beginning of the + * grace period. + */ + synchronize_rcu(); +} + +/* Per-task initial processing. */ +static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop) +{ + if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) { + get_task_struct(t); + t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw); + WRITE_ONCE(t->rcu_tasks_holdout, true); + list_add(&t->rcu_tasks_holdout_list, hop); + } +} + +/* Processing between scanning taskslist and draining the holdout list. */ +void rcu_tasks_postscan(struct list_head *hop) +{ + /* + * Wait for tasks that are in the process of exiting. This + * does only part of the job, ensuring that all tasks that were + * previously exiting reach the point where they have disabled + * preemption, allowing the later synchronize_rcu() to finish + * the job. + */ + synchronize_srcu(&tasks_rcu_exit_srcu); +} + +/* See if tasks are still holding out, complain if so. */ +static void check_holdout_task(struct task_struct *t, + bool needreport, bool *firstreport) +{ + int cpu; + + if (!READ_ONCE(t->rcu_tasks_holdout) || + t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) || + !READ_ONCE(t->on_rq) || + (IS_ENABLED(CONFIG_NO_HZ_FULL) && + !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) { + WRITE_ONCE(t->rcu_tasks_holdout, false); + list_del_init(&t->rcu_tasks_holdout_list); + put_task_struct(t); + return; + } + rcu_request_urgent_qs_task(t); + if (!needreport) + return; + if (*firstreport) { + pr_err("INFO: rcu_tasks detected stalls on tasks:\n"); + *firstreport = false; + } + cpu = task_cpu(t); + pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n", + t, ".I"[is_idle_task(t)], + "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)], + t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout, + t->rcu_tasks_idle_cpu, cpu); + sched_show_task(t); +} + +/* Scan the holdout lists for tasks no longer holding out. */ +static void check_all_holdout_tasks(struct list_head *hop, + bool needreport, bool *firstreport) +{ + struct task_struct *t, *t1; + + list_for_each_entry_safe(t, t1, hop, rcu_tasks_holdout_list) { + check_holdout_task(t, needreport, firstreport); + cond_resched(); + } +} + +/* Finish off the Tasks-RCU grace period. */ +static void rcu_tasks_postgp(struct rcu_tasks *rtp) +{ + /* + * Because ->on_rq and ->nvcsw are not guaranteed to have a full + * memory barriers prior to them in the schedule() path, memory + * reordering on other CPUs could cause their RCU-tasks read-side + * critical sections to extend past the end of the grace period. + * However, because these ->nvcsw updates are carried out with + * interrupts disabled, we can use synchronize_rcu() to force the + * needed ordering on all such CPUs. + * + * This synchronize_rcu() also confines all ->rcu_tasks_holdout + * accesses to be within the grace period, avoiding the need for + * memory barriers for ->rcu_tasks_holdout accesses. + * + * In addition, this synchronize_rcu() waits for exiting tasks + * to complete their final preempt_disable() region of execution, + * cleaning up after the synchronize_srcu() above. + */ + synchronize_rcu(); +} + +void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func); +DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks, "RCU Tasks"); + +/** + * call_rcu_tasks() - Queue an RCU for invocation task-based grace period + * @rhp: structure to be used for queueing the RCU updates. + * @func: actual callback function to be invoked after the grace period + * + * The callback function will be invoked some time after a full grace + * period elapses, in other words after all currently executing RCU + * read-side critical sections have completed. call_rcu_tasks() assumes + * that the read-side critical sections end at a voluntary context + * switch (not a preemption!), cond_resched_rcu_qs(), entry into idle, + * or transition to usermode execution. As such, there are no read-side + * primitives analogous to rcu_read_lock() and rcu_read_unlock() because + * this primitive is intended to determine that all tasks have passed + * through a safe state, not so much for data-strcuture synchronization. + * + * See the description of call_rcu() for more detailed information on + * memory ordering guarantees. + */ +void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func) +{ + call_rcu_tasks_generic(rhp, func, &rcu_tasks); +} +EXPORT_SYMBOL_GPL(call_rcu_tasks); + +/** + * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed. + * + * Control will return to the caller some time after a full rcu-tasks + * grace period has elapsed, in other words after all currently + * executing rcu-tasks read-side critical sections have elapsed. These + * read-side critical sections are delimited by calls to schedule(), + * cond_resched_tasks_rcu_qs(), idle execution, userspace execution, calls + * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched(). + * + * This is a very specialized primitive, intended only for a few uses in + * tracing and other situations requiring manipulation of function + * preambles and profiling hooks. The synchronize_rcu_tasks() function + * is not (yet) intended for heavy use from multiple CPUs. + * + * See the description of synchronize_rcu() for more detailed information + * on memory ordering guarantees. + */ +void synchronize_rcu_tasks(void) +{ + synchronize_rcu_tasks_generic(&rcu_tasks); +} +EXPORT_SYMBOL_GPL(synchronize_rcu_tasks); + +/** + * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks. + * + * Although the current implementation is guaranteed to wait, it is not + * obligated to, for example, if there are no pending callbacks. + */ +void rcu_barrier_tasks(void) +{ + /* There is only one callback queue, so this is easy. ;-) */ + synchronize_rcu_tasks(); +} +EXPORT_SYMBOL_GPL(rcu_barrier_tasks); + +static int __init rcu_spawn_tasks_kthread(void) +{ + rcu_tasks.pregp_func = rcu_tasks_pregp_step; + rcu_tasks.pertask_func = rcu_tasks_pertask; + rcu_tasks.postscan_func = rcu_tasks_postscan; + rcu_tasks.holdouts_func = check_all_holdout_tasks; + rcu_tasks.postgp_func = rcu_tasks_postgp; + rcu_spawn_tasks_kthread_generic(&rcu_tasks); + return 0; +} +core_initcall(rcu_spawn_tasks_kthread); + +static void show_rcu_tasks_classic_gp_kthread(void) +{ + show_rcu_tasks_generic_gp_kthread(&rcu_tasks, ""); +} + +/* Do the srcu_read_lock() for the above synchronize_srcu(). */ +void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu) +{ + preempt_disable(); + current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu); + preempt_enable(); +} + +/* Do the srcu_read_unlock() for the above synchronize_srcu(). */ +void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu) +{ + struct task_struct *t = current; + + preempt_disable(); + __srcu_read_unlock(&tasks_rcu_exit_srcu, t->rcu_tasks_idx); + preempt_enable(); + exit_tasks_rcu_finish_trace(t); +} + +#else /* #ifdef CONFIG_TASKS_RCU */ +static void show_rcu_tasks_classic_gp_kthread(void) { } +void exit_tasks_rcu_start(void) { } +void exit_tasks_rcu_finish(void) { exit_tasks_rcu_finish_trace(current); } +#endif /* #else #ifdef CONFIG_TASKS_RCU */ + +#ifdef CONFIG_TASKS_RUDE_RCU + +//////////////////////////////////////////////////////////////////////// +// +// "Rude" variant of Tasks RCU, inspired by Steve Rostedt's trick of +// passing an empty function to schedule_on_each_cpu(). This approach +// provides an asynchronous call_rcu_tasks_rude() API and batching +// of concurrent calls to the synchronous synchronize_rcu_rude() API. +// This sends IPIs far and wide and induces otherwise unnecessary context +// switches on all online CPUs, whether idle or not. + +// Empty function to allow workqueues to force a context switch. +static void rcu_tasks_be_rude(struct work_struct *work) +{ +} + +// Wait for one rude RCU-tasks grace period. +static void rcu_tasks_rude_wait_gp(struct rcu_tasks *rtp) +{ + rtp->n_ipis += cpumask_weight(cpu_online_mask); + schedule_on_each_cpu(rcu_tasks_be_rude); +} + +void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func); +DEFINE_RCU_TASKS(rcu_tasks_rude, rcu_tasks_rude_wait_gp, call_rcu_tasks_rude, + "RCU Tasks Rude"); + +/** + * call_rcu_tasks_rude() - Queue a callback rude task-based grace period + * @rhp: structure to be used for queueing the RCU updates. + * @func: actual callback function to be invoked after the grace period + * + * The callback function will be invoked some time after a full grace + * period elapses, in other words after all currently executing RCU + * read-side critical sections have completed. call_rcu_tasks_rude() + * assumes that the read-side critical sections end at context switch, + * cond_resched_rcu_qs(), or transition to usermode execution. As such, + * there are no read-side primitives analogous to rcu_read_lock() and + * rcu_read_unlock() because this primitive is intended to determine + * that all tasks have passed through a safe state, not so much for + * data-strcuture synchronization. + * + * See the description of call_rcu() for more detailed information on + * memory ordering guarantees. + */ +void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func) +{ + call_rcu_tasks_generic(rhp, func, &rcu_tasks_rude); +} +EXPORT_SYMBOL_GPL(call_rcu_tasks_rude); + +/** + * synchronize_rcu_tasks_rude - wait for a rude rcu-tasks grace period + * + * Control will return to the caller some time after a rude rcu-tasks + * grace period has elapsed, in other words after all currently + * executing rcu-tasks read-side critical sections have elapsed. These + * read-side critical sections are delimited by calls to schedule(), + * cond_resched_tasks_rcu_qs(), userspace execution, and (in theory, + * anyway) cond_resched(). + * + * This is a very specialized primitive, intended only for a few uses in + * tracing and other situations requiring manipulation of function preambles + * and profiling hooks. The synchronize_rcu_tasks_rude() function is not + * (yet) intended for heavy use from multiple CPUs. + * + * See the description of synchronize_rcu() for more detailed information + * on memory ordering guarantees. + */ +void synchronize_rcu_tasks_rude(void) +{ + synchronize_rcu_tasks_generic(&rcu_tasks_rude); +} +EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_rude); + +/** + * rcu_barrier_tasks_rude - Wait for in-flight call_rcu_tasks_rude() callbacks. + * + * Although the current implementation is guaranteed to wait, it is not + * obligated to, for example, if there are no pending callbacks. + */ +void rcu_barrier_tasks_rude(void) +{ + /* There is only one callback queue, so this is easy. ;-) */ + synchronize_rcu_tasks_rude(); +} +EXPORT_SYMBOL_GPL(rcu_barrier_tasks_rude); + +static int __init rcu_spawn_tasks_rude_kthread(void) +{ + rcu_spawn_tasks_kthread_generic(&rcu_tasks_rude); + return 0; +} +core_initcall(rcu_spawn_tasks_rude_kthread); + +static void show_rcu_tasks_rude_gp_kthread(void) +{ + show_rcu_tasks_generic_gp_kthread(&rcu_tasks_rude, ""); +} + +#else /* #ifdef CONFIG_TASKS_RUDE_RCU */ +static void show_rcu_tasks_rude_gp_kthread(void) {} +#endif /* #else #ifdef CONFIG_TASKS_RUDE_RCU */ + +//////////////////////////////////////////////////////////////////////// +// +// Tracing variant of Tasks RCU. This variant is designed to be used +// to protect tracing hooks, including those of BPF. This variant +// therefore: +// +// 1. Has explicit read-side markers to allow finite grace periods +// in the face of in-kernel loops for PREEMPT=n builds. +// +// 2. Protects code in the idle loop, exception entry/exit, and +// CPU-hotplug code paths, similar to the capabilities of SRCU. +// +// 3. Avoids expensive read-side instruction, having overhead similar +// to that of Preemptible RCU. +// +// There are of course downsides. The grace-period code can send IPIs to +// CPUs, even when those CPUs are in the idle loop or in nohz_full userspace. +// It is necessary to scan the full tasklist, much as for Tasks RCU. There +// is a single callback queue guarded by a single lock, again, much as for +// Tasks RCU. If needed, these downsides can be at least partially remedied. +// +// Perhaps most important, this variant of RCU does not affect the vanilla +// flavors, rcu_preempt and rcu_sched. The fact that RCU Tasks Trace +// readers can operate from idle, offline, and exception entry/exit in no +// way allows rcu_preempt and rcu_sched readers to also do so. + +// The lockdep state must be outside of #ifdef to be useful. +#ifdef CONFIG_DEBUG_LOCK_ALLOC +static struct lock_class_key rcu_lock_trace_key; +struct lockdep_map rcu_trace_lock_map = + STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_trace", &rcu_lock_trace_key); +EXPORT_SYMBOL_GPL(rcu_trace_lock_map); +#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ + +#ifdef CONFIG_TASKS_TRACE_RCU + +atomic_t trc_n_readers_need_end; // Number of waited-for readers. +DECLARE_WAIT_QUEUE_HEAD(trc_wait); // List of holdout tasks. + +// Record outstanding IPIs to each CPU. No point in sending two... +static DEFINE_PER_CPU(bool, trc_ipi_to_cpu); + +// The number of detections of task quiescent state relying on +// heavyweight readers executing explicit memory barriers. +unsigned long n_heavy_reader_attempts; +unsigned long n_heavy_reader_updates; +unsigned long n_heavy_reader_ofl_updates; + +void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func); +DEFINE_RCU_TASKS(rcu_tasks_trace, rcu_tasks_wait_gp, call_rcu_tasks_trace, + "RCU Tasks Trace"); + +/* + * This irq_work handler allows rcu_read_unlock_trace() to be invoked + * while the scheduler locks are held. + */ +static void rcu_read_unlock_iw(struct irq_work *iwp) +{ + wake_up(&trc_wait); +} +static DEFINE_IRQ_WORK(rcu_tasks_trace_iw, rcu_read_unlock_iw); + +/* If we are the last reader, wake up the grace-period kthread. */ +void rcu_read_unlock_trace_special(struct task_struct *t, int nesting) +{ + int nq = t->trc_reader_special.b.need_qs; + + if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && + t->trc_reader_special.b.need_mb) + smp_mb(); // Pairs with update-side barriers. + // Update .need_qs before ->trc_reader_nesting for irq/NMI handlers. + if (nq) + WRITE_ONCE(t->trc_reader_special.b.need_qs, false); + WRITE_ONCE(t->trc_reader_nesting, nesting); + if (nq && atomic_dec_and_test(&trc_n_readers_need_end)) + irq_work_queue(&rcu_tasks_trace_iw); +} +EXPORT_SYMBOL_GPL(rcu_read_unlock_trace_special); + +/* Add a task to the holdout list, if it is not already on the list. */ +static void trc_add_holdout(struct task_struct *t, struct list_head *bhp) +{ + if (list_empty(&t->trc_holdout_list)) { + get_task_struct(t); + list_add(&t->trc_holdout_list, bhp); + } +} + +/* Remove a task from the holdout list, if it is in fact present. */ +static void trc_del_holdout(struct task_struct *t) +{ + if (!list_empty(&t->trc_holdout_list)) { + list_del_init(&t->trc_holdout_list); + put_task_struct(t); + } +} + +/* IPI handler to check task state. */ +static void trc_read_check_handler(void *t_in) +{ + struct task_struct *t = current; + struct task_struct *texp = t_in; + + // If the task is no longer running on this CPU, leave. + if (unlikely(texp != t)) { + if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end))) + wake_up(&trc_wait); + goto reset_ipi; // Already on holdout list, so will check later. + } + + // If the task is not in a read-side critical section, and + // if this is the last reader, awaken the grace-period kthread. + if (likely(!t->trc_reader_nesting)) { + if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end))) + wake_up(&trc_wait); + // Mark as checked after decrement to avoid false + // positives on the above WARN_ON_ONCE(). + WRITE_ONCE(t->trc_reader_checked, true); + goto reset_ipi; + } + WRITE_ONCE(t->trc_reader_checked, true); + + // Get here if the task is in a read-side critical section. Set + // its state so that it will awaken the grace-period kthread upon + // exit from that critical section. + WARN_ON_ONCE(t->trc_reader_special.b.need_qs); + WRITE_ONCE(t->trc_reader_special.b.need_qs, true); + +reset_ipi: + // Allow future IPIs to be sent on CPU and for task. + // Also order this IPI handler against any later manipulations of + // the intended task. + smp_store_release(&per_cpu(trc_ipi_to_cpu, smp_processor_id()), false); // ^^^ + smp_store_release(&texp->trc_ipi_to_cpu, -1); // ^^^ +} + +/* Callback function for scheduler to check locked-down task. */ +static bool trc_inspect_reader(struct task_struct *t, void *arg) +{ + int cpu = task_cpu(t); + bool in_qs = false; + bool ofl = cpu_is_offline(cpu); + + if (task_curr(t)) { + WARN_ON_ONCE(ofl & !is_idle_task(t)); + + // If no chance of heavyweight readers, do it the hard way. + if (!ofl && !IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) + return false; + + // If heavyweight readers are enabled on the remote task, + // we can inspect its state despite its currently running. + // However, we cannot safely change its state. + n_heavy_reader_attempts++; + if (!ofl && // Check for "running" idle tasks on offline CPUs. + !rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting)) + return false; // No quiescent state, do it the hard way. + n_heavy_reader_updates++; + if (ofl) + n_heavy_reader_ofl_updates++; + in_qs = true; + } else { + in_qs = likely(!t->trc_reader_nesting); + } + + // Mark as checked. Because this is called from the grace-period + // kthread, also remove the task from the holdout list. + t->trc_reader_checked = true; + trc_del_holdout(t); + + if (in_qs) + return true; // Already in quiescent state, done!!! + + // The task is in a read-side critical section, so set up its + // state so that it will awaken the grace-period kthread upon exit + // from that critical section. + atomic_inc(&trc_n_readers_need_end); // One more to wait on. + WARN_ON_ONCE(t->trc_reader_special.b.need_qs); + WRITE_ONCE(t->trc_reader_special.b.need_qs, true); + return true; +} + +/* Attempt to extract the state for the specified task. */ +static void trc_wait_for_one_reader(struct task_struct *t, + struct list_head *bhp) +{ + int cpu; + + // If a previous IPI is still in flight, let it complete. + if (smp_load_acquire(&t->trc_ipi_to_cpu) != -1) // Order IPI + return; + + // The current task had better be in a quiescent state. + if (t == current) { + t->trc_reader_checked = true; + trc_del_holdout(t); + WARN_ON_ONCE(t->trc_reader_nesting); + return; + } + + // Attempt to nail down the task for inspection. + get_task_struct(t); + if (try_invoke_on_locked_down_task(t, trc_inspect_reader, NULL)) { + put_task_struct(t); + return; + } + put_task_struct(t); + + // If currently running, send an IPI, either way, add to list. + trc_add_holdout(t, bhp); + if (task_curr(t) && time_after(jiffies, rcu_tasks_trace.gp_start + rcu_task_ipi_delay)) { + // The task is currently running, so try IPIing it. + cpu = task_cpu(t); + + // If there is already an IPI outstanding, let it happen. + if (per_cpu(trc_ipi_to_cpu, cpu) || t->trc_ipi_to_cpu >= 0) + return; + + atomic_inc(&trc_n_readers_need_end); + per_cpu(trc_ipi_to_cpu, cpu) = true; + t->trc_ipi_to_cpu = cpu; + rcu_tasks_trace.n_ipis++; + if (smp_call_function_single(cpu, + trc_read_check_handler, t, 0)) { + // Just in case there is some other reason for + // failure than the target CPU being offline. + rcu_tasks_trace.n_ipis_fails++; + per_cpu(trc_ipi_to_cpu, cpu) = false; + t->trc_ipi_to_cpu = cpu; + if (atomic_dec_and_test(&trc_n_readers_need_end)) { + WARN_ON_ONCE(1); + wake_up(&trc_wait); + } + } + } +} + +/* Initialize for a new RCU-tasks-trace grace period. */ +static void rcu_tasks_trace_pregp_step(void) +{ + int cpu; + + // Allow for fast-acting IPIs. + atomic_set(&trc_n_readers_need_end, 1); + + // There shouldn't be any old IPIs, but... + for_each_possible_cpu(cpu) + WARN_ON_ONCE(per_cpu(trc_ipi_to_cpu, cpu)); + + // Disable CPU hotplug across the tasklist scan. + // This also waits for all readers in CPU-hotplug code paths. + cpus_read_lock(); +} + +/* Do first-round processing for the specified task. */ +static void rcu_tasks_trace_pertask(struct task_struct *t, + struct list_head *hop) +{ + WRITE_ONCE(t->trc_reader_special.b.need_qs, false); + WRITE_ONCE(t->trc_reader_checked, false); + t->trc_ipi_to_cpu = -1; + trc_wait_for_one_reader(t, hop); +} + +/* + * Do intermediate processing between task and holdout scans and + * pick up the idle tasks. + */ +static void rcu_tasks_trace_postscan(struct list_head *hop) +{ + int cpu; + + for_each_possible_cpu(cpu) + rcu_tasks_trace_pertask(idle_task(cpu), hop); + + // Re-enable CPU hotplug now that the tasklist scan has completed. + cpus_read_unlock(); + + // Wait for late-stage exiting tasks to finish exiting. + // These might have passed the call to exit_tasks_rcu_finish(). + synchronize_rcu(); + // Any tasks that exit after this point will set ->trc_reader_checked. +} + +/* Show the state of a task stalling the current RCU tasks trace GP. */ +static void show_stalled_task_trace(struct task_struct *t, bool *firstreport) +{ + int cpu; + + if (*firstreport) { + pr_err("INFO: rcu_tasks_trace detected stalls on tasks:\n"); + *firstreport = false; + } + // FIXME: This should attempt to use try_invoke_on_nonrunning_task(). + cpu = task_cpu(t); + pr_alert("P%d: %c%c%c nesting: %d%c cpu: %d\n", + t->pid, + ".I"[READ_ONCE(t->trc_ipi_to_cpu) > 0], + ".i"[is_idle_task(t)], + ".N"[cpu > 0 && tick_nohz_full_cpu(cpu)], + t->trc_reader_nesting, + " N"[!!t->trc_reader_special.b.need_qs], + cpu); + sched_show_task(t); +} + +/* List stalled IPIs for RCU tasks trace. */ +static void show_stalled_ipi_trace(void) +{ + int cpu; + + for_each_possible_cpu(cpu) + if (per_cpu(trc_ipi_to_cpu, cpu)) + pr_alert("\tIPI outstanding to CPU %d\n", cpu); +} + +/* Do one scan of the holdout list. */ +static void check_all_holdout_tasks_trace(struct list_head *hop, + bool needreport, bool *firstreport) +{ + struct task_struct *g, *t; + + // Disable CPU hotplug across the holdout list scan. + cpus_read_lock(); + + list_for_each_entry_safe(t, g, hop, trc_holdout_list) { + // If safe and needed, try to check the current task. + if (READ_ONCE(t->trc_ipi_to_cpu) == -1 && + !READ_ONCE(t->trc_reader_checked)) + trc_wait_for_one_reader(t, hop); + + // If check succeeded, remove this task from the list. + if (READ_ONCE(t->trc_reader_checked)) + trc_del_holdout(t); + else if (needreport) + show_stalled_task_trace(t, firstreport); + } + + // Re-enable CPU hotplug now that the holdout list scan has completed. + cpus_read_unlock(); + + if (needreport) { + if (firstreport) + pr_err("INFO: rcu_tasks_trace detected stalls? (Late IPI?)\n"); + show_stalled_ipi_trace(); + } +} + +/* Wait for grace period to complete and provide ordering. */ +static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp) +{ + bool firstreport; + struct task_struct *g, *t; + LIST_HEAD(holdouts); + long ret; + + // Remove the safety count. + smp_mb__before_atomic(); // Order vs. earlier atomics + atomic_dec(&trc_n_readers_need_end); + smp_mb__after_atomic(); // Order vs. later atomics + + // Wait for readers. + set_tasks_gp_state(rtp, RTGS_WAIT_READERS); + for (;;) { + ret = wait_event_idle_exclusive_timeout( + trc_wait, + atomic_read(&trc_n_readers_need_end) == 0, + READ_ONCE(rcu_task_stall_timeout)); + if (ret) + break; // Count reached zero. + // Stall warning time, so make a list of the offenders. + for_each_process_thread(g, t) + if (READ_ONCE(t->trc_reader_special.b.need_qs)) + trc_add_holdout(t, &holdouts); + firstreport = true; + list_for_each_entry_safe(t, g, &holdouts, trc_holdout_list) + if (READ_ONCE(t->trc_reader_special.b.need_qs)) { + show_stalled_task_trace(t, &firstreport); + trc_del_holdout(t); + } + if (firstreport) + pr_err("INFO: rcu_tasks_trace detected stalls? (Counter/taskslist mismatch?)\n"); + show_stalled_ipi_trace(); + pr_err("\t%d holdouts\n", atomic_read(&trc_n_readers_need_end)); + } + smp_mb(); // Caller's code must be ordered after wakeup. + // Pairs with pretty much every ordering primitive. +} + +/* Report any needed quiescent state for this exiting task. */ +static void exit_tasks_rcu_finish_trace(struct task_struct *t) +{ + WRITE_ONCE(t->trc_reader_checked, true); + WARN_ON_ONCE(t->trc_reader_nesting); + WRITE_ONCE(t->trc_reader_nesting, 0); + if (WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs))) + rcu_read_unlock_trace_special(t, 0); +} + +/** + * call_rcu_tasks_trace() - Queue a callback trace task-based grace period + * @rhp: structure to be used for queueing the RCU updates. + * @func: actual callback function to be invoked after the grace period + * + * The callback function will be invoked some time after a full grace + * period elapses, in other words after all currently executing RCU + * read-side critical sections have completed. call_rcu_tasks_trace() + * assumes that the read-side critical sections end at context switch, + * cond_resched_rcu_qs(), or transition to usermode execution. As such, + * there are no read-side primitives analogous to rcu_read_lock() and + * rcu_read_unlock() because this primitive is intended to determine + * that all tasks have passed through a safe state, not so much for + * data-strcuture synchronization. + * + * See the description of call_rcu() for more detailed information on + * memory ordering guarantees. + */ +void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func) +{ + call_rcu_tasks_generic(rhp, func, &rcu_tasks_trace); +} +EXPORT_SYMBOL_GPL(call_rcu_tasks_trace); + +/** + * synchronize_rcu_tasks_trace - wait for a trace rcu-tasks grace period + * + * Control will return to the caller some time after a trace rcu-tasks + * grace period has elapsed, in other words after all currently + * executing rcu-tasks read-side critical sections have elapsed. These + * read-side critical sections are delimited by calls to schedule(), + * cond_resched_tasks_rcu_qs(), userspace execution, and (in theory, + * anyway) cond_resched(). + * + * This is a very specialized primitive, intended only for a few uses in + * tracing and other situations requiring manipulation of function preambles + * and profiling hooks. The synchronize_rcu_tasks_trace() function is not + * (yet) intended for heavy use from multiple CPUs. + * + * See the description of synchronize_rcu() for more detailed information + * on memory ordering guarantees. + */ +void synchronize_rcu_tasks_trace(void) +{ + RCU_LOCKDEP_WARN(lock_is_held(&rcu_trace_lock_map), "Illegal synchronize_rcu_tasks_trace() in RCU Tasks Trace read-side critical section"); + synchronize_rcu_tasks_generic(&rcu_tasks_trace); +} +EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_trace); + +/** + * rcu_barrier_tasks_trace - Wait for in-flight call_rcu_tasks_trace() callbacks. + * + * Although the current implementation is guaranteed to wait, it is not + * obligated to, for example, if there are no pending callbacks. + */ +void rcu_barrier_tasks_trace(void) +{ + /* There is only one callback queue, so this is easy. ;-) */ + synchronize_rcu_tasks_trace(); +} +EXPORT_SYMBOL_GPL(rcu_barrier_tasks_trace); + +static int __init rcu_spawn_tasks_trace_kthread(void) +{ + rcu_tasks_trace.pregp_func = rcu_tasks_trace_pregp_step; + rcu_tasks_trace.pertask_func = rcu_tasks_trace_pertask; + rcu_tasks_trace.postscan_func = rcu_tasks_trace_postscan; + rcu_tasks_trace.holdouts_func = check_all_holdout_tasks_trace; + rcu_tasks_trace.postgp_func = rcu_tasks_trace_postgp; + rcu_spawn_tasks_kthread_generic(&rcu_tasks_trace); + return 0; +} +core_initcall(rcu_spawn_tasks_trace_kthread); + +static void show_rcu_tasks_trace_gp_kthread(void) +{ + char buf[64]; + + sprintf(buf, "N%d h:%lu/%lu/%lu", atomic_read(&trc_n_readers_need_end), + data_race(n_heavy_reader_ofl_updates), + data_race(n_heavy_reader_updates), + data_race(n_heavy_reader_attempts)); + show_rcu_tasks_generic_gp_kthread(&rcu_tasks_trace, buf); +} + +#else /* #ifdef CONFIG_TASKS_TRACE_RCU */ +static void exit_tasks_rcu_finish_trace(struct task_struct *t) { } +static inline void show_rcu_tasks_trace_gp_kthread(void) {} +#endif /* #else #ifdef CONFIG_TASKS_TRACE_RCU */ + +void show_rcu_tasks_gp_kthreads(void) +{ + show_rcu_tasks_classic_gp_kthread(); + show_rcu_tasks_rude_gp_kthread(); + show_rcu_tasks_trace_gp_kthread(); +} + +#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ +static inline void rcu_tasks_bootup_oddness(void) {} +void show_rcu_tasks_gp_kthreads(void) {} +#endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e5903669e336..f288477ee1c2 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -238,7 +238,9 @@ void rcu_softirq_qs(void) /* * Record entry into an extended quiescent state. This is only to be - * called when not already in an extended quiescent state. + * called when not already in an extended quiescent state, that is, + * RCU is watching prior to the call to this function and is no longer + * watching upon return. */ static void rcu_dynticks_eqs_enter(void) { @@ -250,8 +252,9 @@ static void rcu_dynticks_eqs_enter(void) * critical sections, and we also must force ordering with the * next idle sojourn. */ + rcu_dynticks_task_trace_enter(); // Before ->dynticks update! seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks); - /* Better be in an extended quiescent state! */ + // RCU is no longer watching. Better be in extended quiescent state! WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && (seq & RCU_DYNTICK_CTRL_CTR)); /* Better not have special action (TLB flush) pending! */ @@ -261,7 +264,8 @@ static void rcu_dynticks_eqs_enter(void) /* * Record exit from an extended quiescent state. This is only to be - * called from an extended quiescent state. + * called from an extended quiescent state, that is, RCU is not watching + * prior to the call to this function and is watching upon return. */ static void rcu_dynticks_eqs_exit(void) { @@ -274,6 +278,8 @@ static void rcu_dynticks_eqs_exit(void) * critical section. */ seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks); + // RCU is now watching. Better not be in an extended quiescent state! + rcu_dynticks_task_trace_exit(); // After ->dynticks update! WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(seq & RCU_DYNTICK_CTRL_CTR)); if (seq & RCU_DYNTICK_CTRL_MASK) { @@ -346,6 +352,28 @@ static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap) } /* + * Return true if the referenced integer is zero while the specified + * CPU remains within a single extended quiescent state. + */ +bool rcu_dynticks_zero_in_eqs(int cpu, int *vp) +{ + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + int snap; + + // If not quiescent, force back to earlier extended quiescent state. + snap = atomic_read(&rdp->dynticks) & ~(RCU_DYNTICK_CTRL_MASK | + RCU_DYNTICK_CTRL_CTR); + + smp_rmb(); // Order ->dynticks and *vp reads. + if (READ_ONCE(*vp)) + return false; // Non-zero, so report failure; + smp_rmb(); // Order *vp read and ->dynticks re-read. + + // If still in the same extended quiescent state, we are good! + return snap == (atomic_read(&rdp->dynticks) & ~RCU_DYNTICK_CTRL_MASK); +} + +/* * Set the special (bottom) bit of the specified CPU so that it * will take special action (such as flushing its TLB) on the * next exit from an extended quiescent state. Returns true if @@ -584,6 +612,7 @@ static void rcu_eqs_enter(bool user) WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && rdp->dynticks_nesting == 0); if (rdp->dynticks_nesting != 1) { + // RCU will still be watching, so just do accounting and leave. rdp->dynticks_nesting--; return; } @@ -596,7 +625,9 @@ static void rcu_eqs_enter(bool user) rcu_prepare_for_idle(); rcu_preempt_deferred_qs(current); WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid irq-access tearing. */ + // RCU is watching here ... rcu_dynticks_eqs_enter(); + // ... but is no longer watching here. rcu_dynticks_task_enter(); } @@ -676,7 +707,9 @@ static __always_inline void rcu_nmi_exit_common(bool irq) if (irq) rcu_prepare_for_idle(); + // RCU is watching here ... rcu_dynticks_eqs_enter(); + // ... but is no longer watching here. if (irq) rcu_dynticks_task_enter(); @@ -751,11 +784,14 @@ static void rcu_eqs_exit(bool user) oldval = rdp->dynticks_nesting; WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0); if (oldval) { + // RCU was already watching, so just do accounting and leave. rdp->dynticks_nesting++; return; } rcu_dynticks_task_exit(); + // RCU is not watching here ... rcu_dynticks_eqs_exit(); + // ... but is watching here. rcu_cleanup_after_idle(); trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, atomic_read(&rdp->dynticks)); WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current)); @@ -832,7 +868,9 @@ static __always_inline void rcu_nmi_enter_common(bool irq) if (irq) rcu_dynticks_task_exit(); + // RCU is not watching here ... rcu_dynticks_eqs_exit(); + // ... but is watching here. if (irq) rcu_cleanup_after_idle(); @@ -842,9 +880,16 @@ static __always_inline void rcu_nmi_enter_common(bool irq) rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE && READ_ONCE(rdp->rcu_urgent_qs) && !READ_ONCE(rdp->rcu_forced_tick)) { + // We get here only if we had already exited the extended + // quiescent state and this was an interrupt (not an NMI). + // Therefore, (1) RCU is already watching and (2) The fact + // that we are in an interrupt handler and that the rcu_node + // lock is an irq-disabled lock prevents self-deadlock. + // So we can safely recheck under the lock. raw_spin_lock_rcu_node(rdp->mynode); - // Recheck under lock. if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) { + // A nohz_full CPU is in the kernel and RCU + // needs a quiescent state. Turn on the tick! WRITE_ONCE(rdp->rcu_forced_tick, true); tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU); } @@ -1486,6 +1531,31 @@ static void rcu_gp_slow(int delay) schedule_timeout_uninterruptible(delay); } +static unsigned long sleep_duration; + +/* Allow rcutorture to stall the grace-period kthread. */ +void rcu_gp_set_torture_wait(int duration) +{ + if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST) && duration > 0) + WRITE_ONCE(sleep_duration, duration); +} +EXPORT_SYMBOL_GPL(rcu_gp_set_torture_wait); + +/* Actually implement the aforementioned wait. */ +static void rcu_gp_torture_wait(void) +{ + unsigned long duration; + + if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST)) + return; + duration = xchg(&sleep_duration, 0UL); + if (duration > 0) { + pr_alert("%s: Waiting %lu jiffies\n", __func__, duration); + schedule_timeout_uninterruptible(duration); + pr_alert("%s: Wait complete\n", __func__); + } +} + /* * Initialize a new grace period. Return false if no grace period required. */ @@ -1693,6 +1763,7 @@ static void rcu_gp_fqs_loop(void) rcu_state.gp_state = RCU_GP_WAIT_FQS; ret = swait_event_idle_timeout_exclusive( rcu_state.gp_wq, rcu_gp_fqs_check_wake(&gf), j); + rcu_gp_torture_wait(); rcu_state.gp_state = RCU_GP_DOING_FQS; /* Locking provides needed memory barriers. */ /* If grace period done, leave loop. */ @@ -1847,6 +1918,7 @@ static int __noreturn rcu_gp_kthread(void *unused) swait_event_idle_exclusive(rcu_state.gp_wq, READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_INIT); + rcu_gp_torture_wait(); rcu_state.gp_state = RCU_GP_DONE_GPS; /* Locking provides needed memory barrier. */ if (rcu_gp_init()) @@ -2837,6 +2909,8 @@ struct kfree_rcu_cpu { struct delayed_work monitor_work; bool monitor_todo; bool initialized; + // Number of objects for which GP not started + int count; }; static DEFINE_PER_CPU(struct kfree_rcu_cpu, krc); @@ -2950,6 +3024,8 @@ static inline bool queue_kfree_rcu_work(struct kfree_rcu_cpu *krcp) krcp->head = NULL; } + WRITE_ONCE(krcp->count, 0); + /* * One work is per one batch, so there are two "free channels", * "bhead_free" and "head_free" the batch can handle. It can be @@ -3086,6 +3162,8 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func) krcp->head = head; } + WRITE_ONCE(krcp->count, krcp->count + 1); + // Set timer to drain after KFREE_DRAIN_JIFFIES. if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING && !krcp->monitor_todo) { @@ -3100,6 +3178,56 @@ unlock_return: } EXPORT_SYMBOL_GPL(kfree_call_rcu); +static unsigned long +kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc) +{ + int cpu; + unsigned long count = 0; + + /* Snapshot count of all CPUs */ + for_each_online_cpu(cpu) { + struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); + + count += READ_ONCE(krcp->count); + } + + return count; +} + +static unsigned long +kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) +{ + int cpu, freed = 0; + unsigned long flags; + + for_each_online_cpu(cpu) { + int count; + struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); + + count = krcp->count; + spin_lock_irqsave(&krcp->lock, flags); + if (krcp->monitor_todo) + kfree_rcu_drain_unlock(krcp, flags); + else + spin_unlock_irqrestore(&krcp->lock, flags); + + sc->nr_to_scan -= count; + freed += count; + + if (sc->nr_to_scan <= 0) + break; + } + + return freed; +} + +static struct shrinker kfree_rcu_shrinker = { + .count_objects = kfree_rcu_shrink_count, + .scan_objects = kfree_rcu_shrink_scan, + .batch = 0, + .seeks = DEFAULT_SEEKS, +}; + void __init kfree_rcu_scheduler_running(void) { int cpu; @@ -4021,6 +4149,8 @@ static void __init kfree_rcu_batch_init(void) INIT_DELAYED_WORK(&krcp->monitor_work, kfree_rcu_monitor); krcp->initialized = true; } + if (register_shrinker(&kfree_rcu_shrinker)) + pr_err("Failed to register kfree_rcu() shrinker!\n"); } void __init rcu_init(void) diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 44edd0a98ffe..43991a40b084 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -455,6 +455,8 @@ static void rcu_bind_gp_kthread(void); static bool rcu_nohz_full_cpu(void); static void rcu_dynticks_task_enter(void); static void rcu_dynticks_task_exit(void); +static void rcu_dynticks_task_trace_enter(void); +static void rcu_dynticks_task_trace_exit(void); /* Forward declarations for tree_stall.h */ static void record_gp_stall_check_time(void); diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index c2b04daf1190..72952edad1e4 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -639,6 +639,7 @@ static void wait_rcu_exp_gp(struct work_struct *wp) */ static void rcu_exp_handler(void *unused) { + int depth = rcu_preempt_depth(); unsigned long flags; struct rcu_data *rdp = this_cpu_ptr(&rcu_data); struct rcu_node *rnp = rdp->mynode; @@ -649,7 +650,7 @@ static void rcu_exp_handler(void *unused) * critical section. If also enabled or idle, immediately * report the quiescent state, otherwise defer. */ - if (!rcu_preempt_depth()) { + if (!depth) { if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) || rcu_dynticks_curr_cpu_in_eqs()) { rcu_report_exp_rdp(rdp); @@ -673,7 +674,7 @@ static void rcu_exp_handler(void *unused) * can have caused this quiescent state to already have been * reported, so we really do need to check ->expmask. */ - if (rcu_preempt_depth() > 0) { + if (depth > 0) { raw_spin_lock_irqsave_rcu_node(rnp, flags); if (rnp->expmask & rdp->grpmask) { rdp->exp_deferred_qs = true; @@ -683,30 +684,8 @@ static void rcu_exp_handler(void *unused) return; } - /* - * The final and least likely case is where the interrupted - * code was just about to or just finished exiting the RCU-preempt - * read-side critical section, and no, we can't tell which. - * So either way, set ->deferred_qs to flag later code that - * a quiescent state is required. - * - * If the CPU is fully enabled (or if some buggy RCU-preempt - * read-side critical section is being used from idle), just - * invoke rcu_preempt_deferred_qs() to immediately report the - * quiescent state. We cannot use rcu_read_unlock_special() - * because we are in an interrupt handler, which will cause that - * function to take an early exit without doing anything. - * - * Otherwise, force a context switch after the CPU enables everything. - */ - rdp->exp_deferred_qs = true; - if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) || - WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs())) { - rcu_preempt_deferred_qs(t); - } else { - set_tsk_need_resched(t); - set_preempt_need_resched(); - } + // Finally, negative nesting depth should not happen. + WARN_ON_ONCE(1); } /* PREEMPTION=y, so no PREEMPTION=n expedited grace period to clean up after. */ diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 5771e32a3840..50caa3fcbad2 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -331,6 +331,7 @@ void rcu_note_context_switch(bool preempt) rcu_qs(); if (rdp->exp_deferred_qs) rcu_report_exp_rdp(rdp); + rcu_tasks_qs(current, preempt); trace_rcu_utilization(TPS("End context switch")); } EXPORT_SYMBOL_GPL(rcu_note_context_switch); @@ -345,9 +346,7 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) return READ_ONCE(rnp->gp_tasks) != NULL; } -/* Bias and limit values for ->rcu_read_lock_nesting. */ -#define RCU_NEST_BIAS INT_MAX -#define RCU_NEST_NMAX (-INT_MAX / 2) +/* limit value for ->rcu_read_lock_nesting. */ #define RCU_NEST_PMAX (INT_MAX / 2) static void rcu_preempt_read_enter(void) @@ -355,9 +354,9 @@ static void rcu_preempt_read_enter(void) current->rcu_read_lock_nesting++; } -static void rcu_preempt_read_exit(void) +static int rcu_preempt_read_exit(void) { - current->rcu_read_lock_nesting--; + return --current->rcu_read_lock_nesting; } static void rcu_preempt_depth_set(int val) @@ -390,21 +389,15 @@ void __rcu_read_unlock(void) { struct task_struct *t = current; - if (rcu_preempt_depth() != 1) { - rcu_preempt_read_exit(); - } else { + if (rcu_preempt_read_exit() == 0) { barrier(); /* critical section before exit code. */ - rcu_preempt_depth_set(-RCU_NEST_BIAS); - barrier(); /* assign before ->rcu_read_unlock_special load */ if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s))) rcu_read_unlock_special(t); - barrier(); /* ->rcu_read_unlock_special load before assign */ - rcu_preempt_depth_set(0); } if (IS_ENABLED(CONFIG_PROVE_LOCKING)) { int rrln = rcu_preempt_depth(); - WARN_ON_ONCE(rrln < 0 && rrln > RCU_NEST_NMAX); + WARN_ON_ONCE(rrln < 0 || rrln > RCU_NEST_PMAX); } } EXPORT_SYMBOL_GPL(__rcu_read_unlock); @@ -556,7 +549,7 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t) { return (__this_cpu_read(rcu_data.exp_deferred_qs) || READ_ONCE(t->rcu_read_unlock_special.s)) && - rcu_preempt_depth() <= 0; + rcu_preempt_depth() == 0; } /* @@ -569,16 +562,11 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t) static void rcu_preempt_deferred_qs(struct task_struct *t) { unsigned long flags; - bool couldrecurse = rcu_preempt_depth() >= 0; if (!rcu_preempt_need_deferred_qs(t)) return; - if (couldrecurse) - rcu_preempt_depth_set(rcu_preempt_depth() - RCU_NEST_BIAS); local_irq_save(flags); rcu_preempt_deferred_qs_irqrestore(t, flags); - if (couldrecurse) - rcu_preempt_depth_set(rcu_preempt_depth() + RCU_NEST_BIAS); } /* @@ -615,19 +603,18 @@ static void rcu_read_unlock_special(struct task_struct *t) struct rcu_data *rdp = this_cpu_ptr(&rcu_data); struct rcu_node *rnp = rdp->mynode; - exp = (t->rcu_blocked_node && t->rcu_blocked_node->exp_tasks) || - (rdp->grpmask & READ_ONCE(rnp->expmask)) || - tick_nohz_full_cpu(rdp->cpu); + exp = (t->rcu_blocked_node && + READ_ONCE(t->rcu_blocked_node->exp_tasks)) || + (rdp->grpmask & READ_ONCE(rnp->expmask)); // Need to defer quiescent state until everything is enabled. - if (irqs_were_disabled && use_softirq && - (in_interrupt() || - (exp && !t->rcu_read_unlock_special.b.deferred_qs))) { - // Using softirq, safe to awaken, and we get - // no help from enabling irqs, unlike bh/preempt. + if (use_softirq && (in_irq() || (exp && !irqs_were_disabled))) { + // Using softirq, safe to awaken, and either the + // wakeup is free or there is an expedited GP. raise_softirq_irqoff(RCU_SOFTIRQ); } else { // Enabling BH or preempt does reschedule, so... - // Also if no expediting or NO_HZ_FULL, slow is OK. + // Also if no expediting, slow is OK. + // Plus nohz_full CPUs eventually get tick enabled. set_tsk_need_resched(current); set_preempt_need_resched(); if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled && @@ -640,7 +627,6 @@ static void rcu_read_unlock_special(struct task_struct *t) irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu); } } - t->rcu_read_unlock_special.b.deferred_qs = true; local_irq_restore(flags); return; } @@ -699,7 +685,7 @@ static void rcu_flavor_sched_clock_irq(int user) } else if (rcu_preempt_need_deferred_qs(t)) { rcu_preempt_deferred_qs(t); /* Report deferred QS. */ return; - } else if (!rcu_preempt_depth()) { + } else if (!WARN_ON_ONCE(rcu_preempt_depth())) { rcu_qs(); /* Report immediate QS. */ return; } @@ -854,8 +840,7 @@ void rcu_note_context_switch(bool preempt) this_cpu_write(rcu_data.rcu_urgent_qs, false); if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) rcu_momentary_dyntick_idle(); - if (!preempt) - rcu_tasks_qs(current); + rcu_tasks_qs(current, preempt); out: trace_rcu_utilization(TPS("End context switch")); } @@ -2568,3 +2553,21 @@ static void rcu_dynticks_task_exit(void) WRITE_ONCE(current->rcu_tasks_idle_cpu, -1); #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ } + +/* Turn on heavyweight RCU tasks trace readers on idle/user entry. */ +static void rcu_dynticks_task_trace_enter(void) +{ +#ifdef CONFIG_TASKS_RCU_TRACE + if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) + current->trc_reader_special.b.need_mb = true; +#endif /* #ifdef CONFIG_TASKS_RCU_TRACE */ +} + +/* Turn off heavyweight RCU tasks trace readers on idle/user exit. */ +static void rcu_dynticks_task_trace_exit(void) +{ +#ifdef CONFIG_TASKS_RCU_TRACE + if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) + current->trc_reader_special.b.need_mb = false; +#endif /* #ifdef CONFIG_TASKS_RCU_TRACE */ +} diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 3a7bc99e78e3..ae76bd329582 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -15,10 +15,12 @@ int sysctl_panic_on_rcu_stall __read_mostly; #ifdef CONFIG_PROVE_RCU -#define RCU_STALL_DELAY_DELTA (5 * HZ) +#define RCU_STALL_DELAY_DELTA (5 * HZ) #else -#define RCU_STALL_DELAY_DELTA 0 +#define RCU_STALL_DELAY_DELTA 0 #endif +#define RCU_STALL_MIGHT_DIV 8 +#define RCU_STALL_MIGHT_MIN (2 * HZ) /* Limit-check stall timeouts specified at boottime and runtime. */ int rcu_jiffies_till_stall_check(void) @@ -40,6 +42,36 @@ int rcu_jiffies_till_stall_check(void) } EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check); +/** + * rcu_gp_might_be_stalled - Is it likely that the grace period is stalled? + * + * Returns @true if the current grace period is sufficiently old that + * it is reasonable to assume that it might be stalled. This can be + * useful when deciding whether to allocate memory to enable RCU-mediated + * freeing on the one hand or just invoking synchronize_rcu() on the other. + * The latter is preferable when the grace period is stalled. + * + * Note that sampling of the .gp_start and .gp_seq fields must be done + * carefully to avoid false positives at the beginnings and ends of + * grace periods. + */ +bool rcu_gp_might_be_stalled(void) +{ + unsigned long d = rcu_jiffies_till_stall_check() / RCU_STALL_MIGHT_DIV; + unsigned long j = jiffies; + + if (d < RCU_STALL_MIGHT_MIN) + d = RCU_STALL_MIGHT_MIN; + smp_mb(); // jiffies before .gp_seq to avoid false positives. + if (!rcu_gp_in_progress()) + return false; + // Long delays at this point avoids false positive, but a delay + // of ULONG_MAX/4 jiffies voids your no-false-positive warranty. + smp_mb(); // .gp_seq before second .gp_start + // And ditto here. + return !time_before(j, READ_ONCE(rcu_state.gp_start) + d); +} + /* Don't do RCU CPU stall warnings during long sysrq printouts. */ void rcu_sysrq_start(void) { @@ -104,8 +136,8 @@ static void record_gp_stall_check_time(void) WRITE_ONCE(rcu_state.gp_start, j); j1 = rcu_jiffies_till_stall_check(); - /* Record ->gp_start before ->jiffies_stall. */ - smp_store_release(&rcu_state.jiffies_stall, j + j1); /* ^^^ */ + smp_mb(); // ->gp_start before ->jiffies_stall and caller's ->gp_seq. + WRITE_ONCE(rcu_state.jiffies_stall, j + j1); rcu_state.jiffies_resched = j + j1 / 2; rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs); } @@ -192,14 +224,40 @@ static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } +// Communicate task state back to the RCU CPU stall warning request. +struct rcu_stall_chk_rdr { + int nesting; + union rcu_special rs; + bool on_blkd_list; +}; + +/* + * Report out the state of a not-running task that is stalling the + * current RCU grace period. + */ +static bool check_slow_task(struct task_struct *t, void *arg) +{ + struct rcu_node *rnp; + struct rcu_stall_chk_rdr *rscrp = arg; + + if (task_curr(t)) + return false; // It is running, so decline to inspect it. + rscrp->nesting = t->rcu_read_lock_nesting; + rscrp->rs = t->rcu_read_unlock_special; + rnp = t->rcu_blocked_node; + rscrp->on_blkd_list = !list_empty(&t->rcu_node_entry); + return true; +} + /* * Scan the current list of tasks blocked within RCU read-side critical * sections, printing out the tid of each. */ static int rcu_print_task_stall(struct rcu_node *rnp) { - struct task_struct *t; int ndetected = 0; + struct rcu_stall_chk_rdr rscr; + struct task_struct *t; if (!rcu_preempt_blocked_readers_cgp(rnp)) return 0; @@ -208,7 +266,15 @@ static int rcu_print_task_stall(struct rcu_node *rnp) t = list_entry(rnp->gp_tasks->prev, struct task_struct, rcu_node_entry); list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { - pr_cont(" P%d", t->pid); + if (!try_invoke_on_locked_down_task(t, check_slow_task, &rscr)) + pr_cont(" P%d", t->pid); + else + pr_cont(" P%d/%d:%c%c%c%c", + t->pid, rscr.nesting, + ".b"[rscr.rs.b.blocked], + ".q"[rscr.rs.b.need_qs], + ".e"[rscr.rs.b.exp_hint], + ".l"[rscr.on_blkd_list]); ndetected++; } pr_cont("\n"); @@ -299,6 +365,16 @@ static const char *gp_state_getname(short gs) return gp_state_names[gs]; } +/* Is the RCU grace-period kthread being starved of CPU time? */ +static bool rcu_is_gp_kthread_starving(unsigned long *jp) +{ + unsigned long j = jiffies - READ_ONCE(rcu_state.gp_activity); + + if (jp) + *jp = j; + return j > 2 * HZ; +} + /* * Print out diagnostic information for the specified stalled CPU. * @@ -313,6 +389,7 @@ static const char *gp_state_getname(short gs) static void print_cpu_stall_info(int cpu) { unsigned long delta; + bool falsepositive; char fast_no_hz[72]; struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); char *ticks_title; @@ -333,7 +410,9 @@ static void print_cpu_stall_info(int cpu) } print_cpu_stall_fast_no_hz(fast_no_hz, cpu); delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq); - pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n", + falsepositive = rcu_is_gp_kthread_starving(NULL) && + rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp)); + pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s%s\n", cpu, "O."[!!cpu_online(cpu)], "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)], @@ -345,8 +424,9 @@ static void print_cpu_stall_info(int cpu) rcu_dynticks_snap(rdp) & 0xfff, rdp->dynticks_nesting, rdp->dynticks_nmi_nesting, rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), - READ_ONCE(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart, - fast_no_hz); + data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart, + fast_no_hz, + falsepositive ? " (false positive?)" : ""); } /* Complain about starvation of grace-period kthread. */ @@ -355,8 +435,7 @@ static void rcu_check_gp_kthread_starvation(void) struct task_struct *gpk = rcu_state.gp_kthread; unsigned long j; - j = jiffies - READ_ONCE(rcu_state.gp_activity); - if (j > 2 * HZ) { + if (rcu_is_gp_kthread_starving(&j)) { pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n", rcu_state.name, j, (long)rcu_seq_current(&rcu_state.gp_seq), @@ -364,6 +443,7 @@ static void rcu_check_gp_kthread_starvation(void) gp_state_getname(rcu_state.gp_state), rcu_state.gp_state, gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1); if (gpk) { + pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name); pr_err("RCU grace-period kthread stack dump:\n"); sched_show_task(gpk); wake_up_process(gpk); @@ -426,8 +506,6 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) rcu_state.name, j - gpa, j, gpa, data_race(jiffies_till_next_fqs), rcu_get_root()->qsmask); - /* In this case, the current CPU might be at fault. */ - sched_show_task(current); } } /* Rewrite if needed in case of slow consoles. */ @@ -615,7 +693,7 @@ void show_rcu_gp_kthreads(void) if (rcu_segcblist_is_offloaded(&rdp->cblist)) show_rcu_nocb_state(rdp); } - /* sched_show_task(rcu_state.gp_kthread); */ + show_rcu_tasks_gp_kthreads(); } EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads); diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index 17f23569e21a..3ce63a91d956 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -41,6 +41,7 @@ #include <linux/sched/isolation.h> #include <linux/kprobes.h> #include <linux/slab.h> +#include <linux/irq_work.h> #define CREATE_TRACE_POINTS @@ -51,6 +52,19 @@ #endif #define MODULE_PARAM_PREFIX "rcupdate." +#ifndef data_race +#define data_race(expr) \ + ({ \ + expr; \ + }) +#endif +#ifndef ASSERT_EXCLUSIVE_WRITER +#define ASSERT_EXCLUSIVE_WRITER(var) do { } while (0) +#endif +#ifndef ASSERT_EXCLUSIVE_ACCESS +#define ASSERT_EXCLUSIVE_ACCESS(var) do { } while (0) +#endif + #ifndef CONFIG_TINY_RCU module_param(rcu_expedited, int, 0); module_param(rcu_normal, int, 0); @@ -501,370 +515,6 @@ int rcu_cpu_stall_suppress_at_boot __read_mostly; // !0 = suppress boot stalls. EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress_at_boot); module_param(rcu_cpu_stall_suppress_at_boot, int, 0444); -#ifdef CONFIG_TASKS_RCU - -/* - * Simple variant of RCU whose quiescent states are voluntary context - * switch, cond_resched_rcu_qs(), user-space execution, and idle. - * As such, grace periods can take one good long time. There are no - * read-side primitives similar to rcu_read_lock() and rcu_read_unlock() - * because this implementation is intended to get the system into a safe - * state for some of the manipulations involved in tracing and the like. - * Finally, this implementation does not support high call_rcu_tasks() - * rates from multiple CPUs. If this is required, per-CPU callback lists - * will be needed. - */ - -/* Global list of callbacks and associated lock. */ -static struct rcu_head *rcu_tasks_cbs_head; -static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head; -static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq); -static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock); - -/* Track exiting tasks in order to allow them to be waited for. */ -DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu); - -/* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */ -#define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10) -static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT; -module_param(rcu_task_stall_timeout, int, 0644); - -static struct task_struct *rcu_tasks_kthread_ptr; - -/** - * call_rcu_tasks() - Queue an RCU for invocation task-based grace period - * @rhp: structure to be used for queueing the RCU updates. - * @func: actual callback function to be invoked after the grace period - * - * The callback function will be invoked some time after a full grace - * period elapses, in other words after all currently executing RCU - * read-side critical sections have completed. call_rcu_tasks() assumes - * that the read-side critical sections end at a voluntary context - * switch (not a preemption!), cond_resched_rcu_qs(), entry into idle, - * or transition to usermode execution. As such, there are no read-side - * primitives analogous to rcu_read_lock() and rcu_read_unlock() because - * this primitive is intended to determine that all tasks have passed - * through a safe state, not so much for data-strcuture synchronization. - * - * See the description of call_rcu() for more detailed information on - * memory ordering guarantees. - */ -void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func) -{ - unsigned long flags; - bool needwake; - - rhp->next = NULL; - rhp->func = func; - raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags); - needwake = !rcu_tasks_cbs_head; - WRITE_ONCE(*rcu_tasks_cbs_tail, rhp); - rcu_tasks_cbs_tail = &rhp->next; - raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags); - /* We can't create the thread unless interrupts are enabled. */ - if (needwake && READ_ONCE(rcu_tasks_kthread_ptr)) - wake_up(&rcu_tasks_cbs_wq); -} -EXPORT_SYMBOL_GPL(call_rcu_tasks); - -/** - * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed. - * - * Control will return to the caller some time after a full rcu-tasks - * grace period has elapsed, in other words after all currently - * executing rcu-tasks read-side critical sections have elapsed. These - * read-side critical sections are delimited by calls to schedule(), - * cond_resched_tasks_rcu_qs(), idle execution, userspace execution, calls - * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched(). - * - * This is a very specialized primitive, intended only for a few uses in - * tracing and other situations requiring manipulation of function - * preambles and profiling hooks. The synchronize_rcu_tasks() function - * is not (yet) intended for heavy use from multiple CPUs. - * - * Note that this guarantee implies further memory-ordering guarantees. - * On systems with more than one CPU, when synchronize_rcu_tasks() returns, - * each CPU is guaranteed to have executed a full memory barrier since the - * end of its last RCU-tasks read-side critical section whose beginning - * preceded the call to synchronize_rcu_tasks(). In addition, each CPU - * having an RCU-tasks read-side critical section that extends beyond - * the return from synchronize_rcu_tasks() is guaranteed to have executed - * a full memory barrier after the beginning of synchronize_rcu_tasks() - * and before the beginning of that RCU-tasks read-side critical section. - * Note that these guarantees include CPUs that are offline, idle, or - * executing in user mode, as well as CPUs that are executing in the kernel. - * - * Furthermore, if CPU A invoked synchronize_rcu_tasks(), which returned - * to its caller on CPU B, then both CPU A and CPU B are guaranteed - * to have executed a full memory barrier during the execution of - * synchronize_rcu_tasks() -- even if CPU A and CPU B are the same CPU - * (but again only if the system has more than one CPU). - */ -void synchronize_rcu_tasks(void) -{ - /* Complain if the scheduler has not started. */ - RCU_LOCKDEP_WARN(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE, - "synchronize_rcu_tasks called too soon"); - - /* Wait for the grace period. */ - wait_rcu_gp(call_rcu_tasks); -} -EXPORT_SYMBOL_GPL(synchronize_rcu_tasks); - -/** - * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks. - * - * Although the current implementation is guaranteed to wait, it is not - * obligated to, for example, if there are no pending callbacks. - */ -void rcu_barrier_tasks(void) -{ - /* There is only one callback queue, so this is easy. ;-) */ - synchronize_rcu_tasks(); -} -EXPORT_SYMBOL_GPL(rcu_barrier_tasks); - -/* See if tasks are still holding out, complain if so. */ -static void check_holdout_task(struct task_struct *t, - bool needreport, bool *firstreport) -{ - int cpu; - - if (!READ_ONCE(t->rcu_tasks_holdout) || - t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) || - !READ_ONCE(t->on_rq) || - (IS_ENABLED(CONFIG_NO_HZ_FULL) && - !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) { - WRITE_ONCE(t->rcu_tasks_holdout, false); - list_del_init(&t->rcu_tasks_holdout_list); - put_task_struct(t); - return; - } - rcu_request_urgent_qs_task(t); - if (!needreport) - return; - if (*firstreport) { - pr_err("INFO: rcu_tasks detected stalls on tasks:\n"); - *firstreport = false; - } - cpu = task_cpu(t); - pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n", - t, ".I"[is_idle_task(t)], - "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)], - t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout, - t->rcu_tasks_idle_cpu, cpu); - sched_show_task(t); -} - -/* RCU-tasks kthread that detects grace periods and invokes callbacks. */ -static int __noreturn rcu_tasks_kthread(void *arg) -{ - unsigned long flags; - struct task_struct *g, *t; - unsigned long lastreport; - struct rcu_head *list; - struct rcu_head *next; - LIST_HEAD(rcu_tasks_holdouts); - int fract; - - /* Run on housekeeping CPUs by default. Sysadm can move if desired. */ - housekeeping_affine(current, HK_FLAG_RCU); - - /* - * Each pass through the following loop makes one check for - * newly arrived callbacks, and, if there are some, waits for - * one RCU-tasks grace period and then invokes the callbacks. - * This loop is terminated by the system going down. ;-) - */ - for (;;) { - - /* Pick up any new callbacks. */ - raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags); - list = rcu_tasks_cbs_head; - rcu_tasks_cbs_head = NULL; - rcu_tasks_cbs_tail = &rcu_tasks_cbs_head; - raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags); - - /* If there were none, wait a bit and start over. */ - if (!list) { - wait_event_interruptible(rcu_tasks_cbs_wq, - READ_ONCE(rcu_tasks_cbs_head)); - if (!rcu_tasks_cbs_head) { - WARN_ON(signal_pending(current)); - schedule_timeout_interruptible(HZ/10); - } - continue; - } - - /* - * Wait for all pre-existing t->on_rq and t->nvcsw - * transitions to complete. Invoking synchronize_rcu() - * suffices because all these transitions occur with - * interrupts disabled. Without this synchronize_rcu(), - * a read-side critical section that started before the - * grace period might be incorrectly seen as having started - * after the grace period. - * - * This synchronize_rcu() also dispenses with the - * need for a memory barrier on the first store to - * ->rcu_tasks_holdout, as it forces the store to happen - * after the beginning of the grace period. - */ - synchronize_rcu(); - - /* - * There were callbacks, so we need to wait for an - * RCU-tasks grace period. Start off by scanning - * the task list for tasks that are not already - * voluntarily blocked. Mark these tasks and make - * a list of them in rcu_tasks_holdouts. - */ - rcu_read_lock(); - for_each_process_thread(g, t) { - if (t != current && READ_ONCE(t->on_rq) && - !is_idle_task(t)) { - get_task_struct(t); - t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw); - WRITE_ONCE(t->rcu_tasks_holdout, true); - list_add(&t->rcu_tasks_holdout_list, - &rcu_tasks_holdouts); - } - } - rcu_read_unlock(); - - /* - * Wait for tasks that are in the process of exiting. - * This does only part of the job, ensuring that all - * tasks that were previously exiting reach the point - * where they have disabled preemption, allowing the - * later synchronize_rcu() to finish the job. - */ - synchronize_srcu(&tasks_rcu_exit_srcu); - - /* - * Each pass through the following loop scans the list - * of holdout tasks, removing any that are no longer - * holdouts. When the list is empty, we are done. - */ - lastreport = jiffies; - - /* Start off with HZ/10 wait and slowly back off to 1 HZ wait*/ - fract = 10; - - for (;;) { - bool firstreport; - bool needreport; - int rtst; - struct task_struct *t1; - - if (list_empty(&rcu_tasks_holdouts)) - break; - - /* Slowly back off waiting for holdouts */ - schedule_timeout_interruptible(HZ/fract); - - if (fract > 1) - fract--; - - rtst = READ_ONCE(rcu_task_stall_timeout); - needreport = rtst > 0 && - time_after(jiffies, lastreport + rtst); - if (needreport) - lastreport = jiffies; - firstreport = true; - WARN_ON(signal_pending(current)); - list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts, - rcu_tasks_holdout_list) { - check_holdout_task(t, needreport, &firstreport); - cond_resched(); - } - } - - /* - * Because ->on_rq and ->nvcsw are not guaranteed - * to have a full memory barriers prior to them in the - * schedule() path, memory reordering on other CPUs could - * cause their RCU-tasks read-side critical sections to - * extend past the end of the grace period. However, - * because these ->nvcsw updates are carried out with - * interrupts disabled, we can use synchronize_rcu() - * to force the needed ordering on all such CPUs. - * - * This synchronize_rcu() also confines all - * ->rcu_tasks_holdout accesses to be within the grace - * period, avoiding the need for memory barriers for - * ->rcu_tasks_holdout accesses. - * - * In addition, this synchronize_rcu() waits for exiting - * tasks to complete their final preempt_disable() region - * of execution, cleaning up after the synchronize_srcu() - * above. - */ - synchronize_rcu(); - - /* Invoke the callbacks. */ - while (list) { - next = list->next; - local_bh_disable(); - list->func(list); - local_bh_enable(); - list = next; - cond_resched(); - } - /* Paranoid sleep to keep this from entering a tight loop */ - schedule_timeout_uninterruptible(HZ/10); - } -} - -/* Spawn rcu_tasks_kthread() at core_initcall() time. */ -static int __init rcu_spawn_tasks_kthread(void) -{ - struct task_struct *t; - - t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread"); - if (WARN_ONCE(IS_ERR(t), "%s: Could not start Tasks-RCU grace-period kthread, OOM is now expected behavior\n", __func__)) - return 0; - smp_mb(); /* Ensure others see full kthread. */ - WRITE_ONCE(rcu_tasks_kthread_ptr, t); - return 0; -} -core_initcall(rcu_spawn_tasks_kthread); - -/* Do the srcu_read_lock() for the above synchronize_srcu(). */ -void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu) -{ - preempt_disable(); - current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu); - preempt_enable(); -} - -/* Do the srcu_read_unlock() for the above synchronize_srcu(). */ -void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu) -{ - preempt_disable(); - __srcu_read_unlock(&tasks_rcu_exit_srcu, current->rcu_tasks_idx); - preempt_enable(); -} - -#endif /* #ifdef CONFIG_TASKS_RCU */ - -#ifndef CONFIG_TINY_RCU - -/* - * Print any non-default Tasks RCU settings. - */ -static void __init rcu_tasks_bootup_oddness(void) -{ -#ifdef CONFIG_TASKS_RCU - if (rcu_task_stall_timeout != RCU_TASK_STALL_TIMEOUT) - pr_info("\tTasks-RCU CPU stall warnings timeout set to %d (rcu_task_stall_timeout).\n", rcu_task_stall_timeout); - else - pr_info("\tTasks RCU enabled.\n"); -#endif /* #ifdef CONFIG_TASKS_RCU */ -} - -#endif /* #ifndef CONFIG_TINY_RCU */ - #ifdef CONFIG_PROVE_RCU /* @@ -935,6 +585,8 @@ late_initcall(rcu_verify_early_boot_tests); void rcu_early_boot_tests(void) {} #endif /* CONFIG_PROVE_RCU */ +#include "tasks.h" + #ifndef CONFIG_TINY_RCU /* |