From f505d4346f6129d4708338491cf23ca9cf1d8f2a Mon Sep 17 00:00:00 2001 From: Jakub Kicinski Date: Wed, 16 Sep 2020 11:45:26 -0700 Subject: srcu: Use a more appropriate lockdep helper The lockdep_is_held() macro is defined as: #define lockdep_is_held(lock) lock_is_held(&(lock)->dep_map) This hides away the dereference, so that builds with !LOCKDEP don't break. This works in current kernels because the RCU_LOCKDEP_WARN() eliminates its condition at preprocessor time in !LOCKDEP kernels. However, later patches in this series will cause the compiler to see this condition even in !LOCKDEP kernels. This commit prepares for this upcoming change by switching from lock_is_held() to lockdep_is_held(). Signed-off-by: Jakub Kicinski -- CC: jiangshanlai@gmail.com CC: paulmck@kernel.org CC: josh@joshtriplett.org CC: rostedt@goodmis.org CC: mathieu.desnoyers@efficios.com Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index c13348ee80a5..6cd6fa2f272c 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -906,7 +906,7 @@ static void __synchronize_srcu(struct srcu_struct *ssp, bool do_norm) { struct rcu_synchronize rcu; - RCU_LOCKDEP_WARN(lock_is_held(&ssp->dep_map) || + RCU_LOCKDEP_WARN(lockdep_is_held(ssp) || lock_is_held(&rcu_bh_lock_map) || lock_is_held(&rcu_lock_map) || lock_is_held(&rcu_sched_lock_map), -- cgit v1.2.3-59-g8ed1b From 77dc174103fdb121c47621e9856d73704b7eddd2 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 15 Sep 2020 15:41:50 -0700 Subject: rcu-tasks: Convert rcu_tasks_wait_gp() for-loop to while-loop The infinite for-loop in rcu_tasks_wait_gp() has its only exit at the top of the loop, so this commit does the straightforward conversion to a while-loop, thus saving a few lines. Signed-off-by: Paul E. McKenney --- kernel/rcu/tasks.h | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index d5d9f2d03e8a..a93271fc2572 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -338,14 +338,11 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) if (fract > HZ) fract = HZ; - for (;;) { + while (!list_empty(&holdouts)) { 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_idle(HZ/fract); -- cgit v1.2.3-59-g8ed1b From 27c0f1448389baf7f309b69e62d4b531c9395e88 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 15 Sep 2020 17:08:03 -0700 Subject: rcutorture: Make grace-period kthread report match RCU flavor being tested At the end of the test and after rcu_torture_writer() stalls, rcutorture invokes show_rcu_gp_kthreads() in order to dump out information on the RCU grace-period kthread. This makes a lot of sense when testing vanilla RCU, but not so much for the other flavors. This commit therefore allows per-flavor kthread-dump functions to be specified. [ paulmck: Apply feedback from kernel test robot . ] Signed-off-by: Paul E. McKenney --- kernel/rcu/rcu.h | 16 ++++++++++++++++ kernel/rcu/rcutorture.c | 11 +++++++++-- kernel/rcu/tasks.h | 30 ++++++++++++++---------------- 3 files changed, 39 insertions(+), 18 deletions(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index e01cba5e4b52..59ef1ae6dc37 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -533,4 +533,20 @@ static inline bool rcu_is_nocb_cpu(int cpu) { return false; } static inline void rcu_bind_current_to_nocb(void) { } #endif +#if !defined(CONFIG_TINY_RCU) && defined(CONFIG_TASKS_RCU) +void show_rcu_tasks_classic_gp_kthread(void); +#else +static inline void show_rcu_tasks_classic_gp_kthread(void) {} +#endif +#if !defined(CONFIG_TINY_RCU) && defined(CONFIG_TASKS_RUDE_RCU) +void show_rcu_tasks_rude_gp_kthread(void); +#else +static inline void show_rcu_tasks_rude_gp_kthread(void) {} +#endif +#if !defined(CONFIG_TINY_RCU) && defined(CONFIG_TASKS_TRACE_RCU) +void show_rcu_tasks_trace_gp_kthread(void); +#else +static inline void show_rcu_tasks_trace_gp_kthread(void) {} +#endif + #endif /* __LINUX_RCU_H */ diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index 916ea4f66e4b..c811f23692bf 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -317,6 +317,7 @@ struct rcu_torture_ops { void (*cb_barrier)(void); void (*fqs)(void); void (*stats)(void); + void (*gp_kthread_dbg)(void); int (*stall_dur)(void); int irq_capable; int can_boost; @@ -466,6 +467,7 @@ static struct rcu_torture_ops rcu_ops = { .cb_barrier = rcu_barrier, .fqs = rcu_force_quiescent_state, .stats = NULL, + .gp_kthread_dbg = show_rcu_gp_kthreads, .stall_dur = rcu_jiffies_till_stall_check, .irq_capable = 1, .can_boost = rcu_can_boost(), @@ -693,6 +695,7 @@ static struct rcu_torture_ops tasks_ops = { .exp_sync = synchronize_rcu_mult_test, .call = call_rcu_tasks, .cb_barrier = rcu_barrier_tasks, + .gp_kthread_dbg = show_rcu_tasks_classic_gp_kthread, .fqs = NULL, .stats = NULL, .irq_capable = 1, @@ -762,6 +765,7 @@ static struct rcu_torture_ops tasks_rude_ops = { .exp_sync = synchronize_rcu_tasks_rude, .call = call_rcu_tasks_rude, .cb_barrier = rcu_barrier_tasks_rude, + .gp_kthread_dbg = show_rcu_tasks_rude_gp_kthread, .fqs = NULL, .stats = NULL, .irq_capable = 1, @@ -800,6 +804,7 @@ static struct rcu_torture_ops tasks_tracing_ops = { .exp_sync = synchronize_rcu_tasks_trace, .call = call_rcu_tasks_trace, .cb_barrier = rcu_barrier_tasks_trace, + .gp_kthread_dbg = show_rcu_tasks_trace_gp_kthread, .fqs = NULL, .stats = NULL, .irq_capable = 1, @@ -1594,7 +1599,8 @@ rcu_torture_stats_print(void) sched_show_task(wtp); splatted = true; } - show_rcu_gp_kthreads(); + if (cur_ops->gp_kthread_dbg) + cur_ops->gp_kthread_dbg(); rcu_ftrace_dump(DUMP_ALL); } rtcv_snap = rcu_torture_current_version; @@ -2472,7 +2478,8 @@ rcu_torture_cleanup(void) return; } - show_rcu_gp_kthreads(); + if (cur_ops->gp_kthread_dbg) + cur_ops->gp_kthread_dbg(); rcu_torture_read_exit_cleanup(); rcu_torture_barrier_cleanup(); rcu_torture_fwd_prog_cleanup(); diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index a93271fc2572..0b459890fdcc 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -290,7 +290,7 @@ static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s) ".C"[!!data_race(rtp->cbs_head)], s); } -#endif /* #ifndef CONFIG_TINY_RCU */ +#endif // #ifndef CONFIG_TINY_RCU static void exit_tasks_rcu_finish_trace(struct task_struct *t); @@ -568,12 +568,13 @@ static int __init rcu_spawn_tasks_kthread(void) } core_initcall(rcu_spawn_tasks_kthread); -#ifndef CONFIG_TINY_RCU -static void show_rcu_tasks_classic_gp_kthread(void) +#if !defined(CONFIG_TINY_RCU) +void show_rcu_tasks_classic_gp_kthread(void) { show_rcu_tasks_generic_gp_kthread(&rcu_tasks, ""); } -#endif /* #ifndef CONFIG_TINY_RCU */ +EXPORT_SYMBOL_GPL(show_rcu_tasks_classic_gp_kthread); +#endif // !defined(CONFIG_TINY_RCU) /* Do the srcu_read_lock() for the above synchronize_srcu(). */ void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu) @@ -595,7 +596,6 @@ void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu) } #else /* #ifdef CONFIG_TASKS_RCU */ -static inline 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 */ @@ -696,16 +696,14 @@ static int __init rcu_spawn_tasks_rude_kthread(void) } core_initcall(rcu_spawn_tasks_rude_kthread); -#ifndef CONFIG_TINY_RCU -static void show_rcu_tasks_rude_gp_kthread(void) +#if !defined(CONFIG_TINY_RCU) +void show_rcu_tasks_rude_gp_kthread(void) { show_rcu_tasks_generic_gp_kthread(&rcu_tasks_rude, ""); } -#endif /* #ifndef CONFIG_TINY_RCU */ - -#else /* #ifdef CONFIG_TASKS_RUDE_RCU */ -static void show_rcu_tasks_rude_gp_kthread(void) {} -#endif /* #else #ifdef CONFIG_TASKS_RUDE_RCU */ +EXPORT_SYMBOL_GPL(show_rcu_tasks_rude_gp_kthread); +#endif // !defined(CONFIG_TINY_RCU) +#endif /* #ifdef CONFIG_TASKS_RUDE_RCU */ //////////////////////////////////////////////////////////////////////// // @@ -1199,8 +1197,8 @@ static int __init rcu_spawn_tasks_trace_kthread(void) } core_initcall(rcu_spawn_tasks_trace_kthread); -#ifndef CONFIG_TINY_RCU -static void show_rcu_tasks_trace_gp_kthread(void) +#if !defined(CONFIG_TINY_RCU) +void show_rcu_tasks_trace_gp_kthread(void) { char buf[64]; @@ -1210,11 +1208,11 @@ static void show_rcu_tasks_trace_gp_kthread(void) data_race(n_heavy_reader_attempts)); show_rcu_tasks_generic_gp_kthread(&rcu_tasks_trace, buf); } -#endif /* #ifndef CONFIG_TINY_RCU */ +EXPORT_SYMBOL_GPL(show_rcu_tasks_trace_gp_kthread); +#endif // !defined(CONFIG_TINY_RCU) #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 */ #ifndef CONFIG_TINY_RCU -- cgit v1.2.3-59-g8ed1b From 0c6d18d84db11840dd0f3f65750c6ea0bb6b8e0d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 27 Aug 2020 09:58:19 -0700 Subject: refscale: Bounds-check module parameters The default value for refscale.nreaders is -1, which results in the code setting the value to three-quarters of the number of CPUs. On single-CPU systems, this results in three-quarters of the value one, which the C language's integer arithmetic rounds to zero. This in turn results in a divide-by-zero error. This commit therefore adds bounds checking to the refscale module parameters, so that if they are less than one, they are set to the value one. Reported-by: kernel test robot Tested-by "Chen, Rong A" Signed-off-by: Paul E. McKenney --- kernel/rcu/refscale.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'kernel/rcu') diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c index 952595c678b3..fb5f20d9486a 100644 --- a/kernel/rcu/refscale.c +++ b/kernel/rcu/refscale.c @@ -681,6 +681,12 @@ ref_scale_init(void) // Reader tasks (default to ~75% of online CPUs). if (nreaders < 0) nreaders = (num_online_cpus() >> 1) + (num_online_cpus() >> 2); + if (WARN_ONCE(loops <= 0, "%s: loops = %ld, adjusted to 1\n", __func__, loops)) + loops = 1; + if (WARN_ONCE(nreaders <= 0, "%s: nreaders = %d, adjusted to 1\n", __func__, nreaders)) + nreaders = 1; + if (WARN_ONCE(nruns <= 0, "%s: nruns = %d, adjusted to 1\n", __func__, nruns)) + nruns = 1; reader_tasks = kcalloc(nreaders, sizeof(reader_tasks[0]), GFP_KERNEL); if (!reader_tasks) { -- cgit v1.2.3-59-g8ed1b From 3fcd6a230fa7d03bffcb831a81b40435c146c12b Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 3 Sep 2020 15:23:29 -0700 Subject: x86/cpu: Avoid cpuinfo-induced IPIing of idle CPUs Currently, accessing /proc/cpuinfo sends IPIs to idle CPUs in order to learn their clock frequency. Which is a bit strange, given that waking them from idle likely significantly changes their clock frequency. This commit therefore avoids sending /proc/cpuinfo-induced IPIs to idle CPUs. [ paulmck: Also check for idle in arch_freq_prepare_all(). ] Signed-off-by: Paul E. McKenney Cc: Rafael J. Wysocki Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: "H. Peter Anvin" Cc: --- arch/x86/kernel/cpu/aperfmperf.c | 6 ++++++ include/linux/rcutiny.h | 2 ++ include/linux/rcutree.h | 1 + kernel/rcu/tree.c | 8 ++++++++ 4 files changed, 17 insertions(+) (limited to 'kernel/rcu') diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c index dd3261dab0fb..22911deacb6e 100644 --- a/arch/x86/kernel/cpu/aperfmperf.c +++ b/arch/x86/kernel/cpu/aperfmperf.c @@ -14,6 +14,7 @@ #include #include #include +#include #include "cpu.h" @@ -93,6 +94,9 @@ unsigned int aperfmperf_get_khz(int cpu) if (!housekeeping_cpu(cpu, HK_FLAG_MISC)) return 0; + if (rcu_is_idle_cpu(cpu)) + return 0; /* Idle CPUs are completely uninteresting. */ + aperfmperf_snapshot_cpu(cpu, ktime_get(), true); return per_cpu(samples.khz, cpu); } @@ -112,6 +116,8 @@ void arch_freq_prepare_all(void) for_each_online_cpu(cpu) { if (!housekeeping_cpu(cpu, HK_FLAG_MISC)) continue; + if (rcu_is_idle_cpu(cpu)) + continue; /* Idle CPUs are completely uninteresting. */ if (!aperfmperf_snapshot_cpu(cpu, now, false)) wait = true; } diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 7c1ecdb356d8..2a97334eb786 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -89,6 +89,8 @@ static inline void rcu_irq_enter_irqson(void) { } static inline void rcu_irq_exit(void) { } static inline void rcu_irq_exit_preempt(void) { } static inline void rcu_irq_exit_check_preempt(void) { } +#define rcu_is_idle_cpu(cpu) \ + (is_idle_task(current) && !in_nmi() && !in_irq() && !in_serving_softirq()) static inline void exit_rcu(void) { } static inline bool rcu_preempt_need_deferred_qs(struct task_struct *t) { diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 59eb5cd567d7..df578b73960f 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -50,6 +50,7 @@ void rcu_irq_exit(void); void rcu_irq_exit_preempt(void); void rcu_irq_enter_irqson(void); void rcu_irq_exit_irqson(void); +bool rcu_is_idle_cpu(int cpu); #ifdef CONFIG_PROVE_RCU void rcu_irq_exit_check_preempt(void); diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 06895ef85d69..1d84c0b6a9f3 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -341,6 +341,14 @@ static bool rcu_dynticks_in_eqs(int snap) return !(snap & RCU_DYNTICK_CTRL_CTR); } +/* Return true if the specified CPU is currently idle from an RCU viewpoint. */ +bool rcu_is_idle_cpu(int cpu) +{ + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + + return rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp)); +} + /* * Return true if the CPU corresponding to the specified rcu_data * structure has spent some time in an extended quiescent state since -- cgit v1.2.3-59-g8ed1b From 899f317e4886f916ed21027177177c11b577cea1 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 9 Sep 2020 12:27:03 -0700 Subject: rcuscale: Add RCU Tasks Trace This commit adds the ability to test performance and scalability of RCU Tasks Trace updaters. Reported-by: Alexei Starovoitov Signed-off-by: Paul E. McKenney --- kernel/rcu/rcuscale.c | 32 +++++++++++++++++++++- .../selftests/rcutorture/configs/rcuscale/CFcommon | 3 ++ .../selftests/rcutorture/configs/rcuscale/TRACE01 | 15 ++++++++++ .../rcutorture/configs/rcuscale/TRACE01.boot | 1 + 4 files changed, 50 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01 create mode 100644 tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01.boot (limited to 'kernel/rcu') diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c index 2819b95479af..c42f2401c374 100644 --- a/kernel/rcu/rcuscale.c +++ b/kernel/rcu/rcuscale.c @@ -38,6 +38,7 @@ #include #include #include +#include #include "rcu.h" @@ -294,6 +295,35 @@ static struct rcu_scale_ops tasks_ops = { .name = "tasks" }; +/* + * Definitions for RCU-tasks-trace scalability testing. + */ + +static int tasks_trace_scale_read_lock(void) +{ + rcu_read_lock_trace(); + return 0; +} + +static void tasks_trace_scale_read_unlock(int idx) +{ + rcu_read_unlock_trace(); +} + +static struct rcu_scale_ops tasks_tracing_ops = { + .ptype = RCU_TASKS_FLAVOR, + .init = rcu_sync_scale_init, + .readlock = tasks_trace_scale_read_lock, + .readunlock = tasks_trace_scale_read_unlock, + .get_gp_seq = rcu_no_completed, + .gp_diff = rcu_seq_diff, + .async = call_rcu_tasks_trace, + .gp_barrier = rcu_barrier_tasks_trace, + .sync = synchronize_rcu_tasks_trace, + .exp_sync = synchronize_rcu_tasks_trace, + .name = "tasks-tracing" +}; + static unsigned long rcuscale_seq_diff(unsigned long new, unsigned long old) { if (!cur_ops->gp_diff) @@ -754,7 +784,7 @@ rcu_scale_init(void) long i; int firsterr = 0; static struct rcu_scale_ops *scale_ops[] = { - &rcu_ops, &srcu_ops, &srcud_ops, &tasks_ops, + &rcu_ops, &srcu_ops, &srcud_ops, &tasks_ops, &tasks_tracing_ops }; if (!torture_init_begin(scale_type, verbose)) diff --git a/tools/testing/selftests/rcutorture/configs/rcuscale/CFcommon b/tools/testing/selftests/rcutorture/configs/rcuscale/CFcommon index 87caa0e932c7..90942bb5bebc 100644 --- a/tools/testing/selftests/rcutorture/configs/rcuscale/CFcommon +++ b/tools/testing/selftests/rcutorture/configs/rcuscale/CFcommon @@ -1,2 +1,5 @@ CONFIG_RCU_SCALE_TEST=y CONFIG_PRINTK_TIME=y +CONFIG_TASKS_RCU_GENERIC=y +CONFIG_TASKS_RCU=y +CONFIG_TASKS_TRACE_RCU=y diff --git a/tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01 b/tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01 new file mode 100644 index 000000000000..e6baa2fbaeb3 --- /dev/null +++ b/tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01 @@ -0,0 +1,15 @@ +CONFIG_SMP=y +CONFIG_PREEMPT_NONE=y +CONFIG_PREEMPT_VOLUNTARY=n +CONFIG_PREEMPT=n +CONFIG_HZ_PERIODIC=n +CONFIG_NO_HZ_IDLE=y +CONFIG_NO_HZ_FULL=n +CONFIG_RCU_FAST_NO_HZ=n +CONFIG_RCU_NOCB_CPU=n +CONFIG_DEBUG_LOCK_ALLOC=n +CONFIG_PROVE_LOCKING=n +CONFIG_RCU_BOOST=n +CONFIG_DEBUG_OBJECTS_RCU_HEAD=n +CONFIG_RCU_EXPERT=y +CONFIG_RCU_TRACE=y diff --git a/tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01.boot b/tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01.boot new file mode 100644 index 000000000000..af0aff1457a4 --- /dev/null +++ b/tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01.boot @@ -0,0 +1 @@ +rcuscale.scale_type=tasks-tracing -- cgit v1.2.3-59-g8ed1b From 2f2214d43ccd27ac6d124287107c136a0f7c6053 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 17 Sep 2020 10:30:46 -0700 Subject: rcuscale: Prevent hangs for invalid arguments If an rcuscale torture-test run is given a bad kvm.sh argument, the test will complain to the console, which is good. What is bad is that from the user's perspective, it will just hang for the time specified by the --duration argument. This commit therefore forces an immediate kernel shutdown if a rcu_scale_init()-time error occurs, thus avoiding the appearance of a hang. It also forces a console splat in this case to clearly indicate the presence of an error. Signed-off-by: Paul E. McKenney --- kernel/rcu/rcuscale.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c index c42f2401c374..06491d5530db 100644 --- a/kernel/rcu/rcuscale.c +++ b/kernel/rcu/rcuscale.c @@ -802,7 +802,6 @@ rcu_scale_init(void) for (i = 0; i < ARRAY_SIZE(scale_ops); i++) pr_cont(" %s", scale_ops[i]->name); pr_cont("\n"); - WARN_ON(!IS_MODULE(CONFIG_RCU_SCALE_TEST)); firsterr = -EINVAL; cur_ops = NULL; goto unwind; @@ -876,6 +875,10 @@ rcu_scale_init(void) unwind: torture_init_end(); rcu_scale_cleanup(); + if (shutdown) { + WARN_ON(!IS_MODULE(CONFIG_RCU_SCALE_TEST)); + kernel_power_off(); + } return firsterr; } -- cgit v1.2.3-59-g8ed1b From bc80d353b3f565138cda7e95ed4020e6e69360b2 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 17 Sep 2020 10:37:10 -0700 Subject: refscale: Prevent hangs for invalid arguments If an refscale torture-test run is given a bad kvm.sh argument, the test will complain to the console, which is good. What is bad is that from the user's perspective, it will just hang for the time specified by the --duration argument. This commit therefore forces an immediate kernel shutdown if a ref_scale_init()-time error occurs, thus avoiding the appearance of a hang. It also forces a console splat in this case to clearly indicate the presence of an error. Signed-off-by: Paul E. McKenney --- kernel/rcu/refscale.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c index fb5f20d9486a..23ff36a66f97 100644 --- a/kernel/rcu/refscale.c +++ b/kernel/rcu/refscale.c @@ -658,7 +658,6 @@ ref_scale_init(void) for (i = 0; i < ARRAY_SIZE(scale_ops); i++) pr_cont(" %s", scale_ops[i]->name); pr_cont("\n"); - WARN_ON(!IS_MODULE(CONFIG_RCU_REF_SCALE_TEST)); firsterr = -EINVAL; cur_ops = NULL; goto unwind; @@ -718,6 +717,10 @@ ref_scale_init(void) unwind: torture_init_end(); ref_scale_cleanup(); + if (shutdown) { + WARN_ON(!IS_MODULE(CONFIG_RCU_REF_SCALE_TEST)); + kernel_power_off(); + } return firsterr; } -- cgit v1.2.3-59-g8ed1b From 4994684ce10924a0302567c315c91b0a64eeef46 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 18 Sep 2020 13:30:33 -0700 Subject: rcutorture: Prevent hangs for invalid arguments If an rcutorture torture-test run is given a bad kvm.sh argument, the test will complain to the console, which is good. What is bad is that from the user's perspective, it will just hang for the time specified by the --duration argument. This commit therefore forces an immediate kernel shutdown if a rcu_torture_init()-time error occurs, thus avoiding the appearance of a hang. It also forces a console splat in this case to clearly indicate the presence of an error. Signed-off-by: Paul E. McKenney --- kernel/rcu/rcutorture.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index 916ea4f66e4b..db3767110c60 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -2647,7 +2647,6 @@ rcu_torture_init(void) for (i = 0; i < ARRAY_SIZE(torture_ops); i++) pr_cont(" %s", torture_ops[i]->name); pr_cont("\n"); - WARN_ON(!IS_MODULE(CONFIG_RCU_TORTURE_TEST)); firsterr = -EINVAL; cur_ops = NULL; goto unwind; @@ -2815,6 +2814,10 @@ rcu_torture_init(void) unwind: torture_init_end(); rcu_torture_cleanup(); + if (shutdown_secs) { + WARN_ON(!IS_MODULE(CONFIG_RCU_TORTURE_TEST)); + kernel_power_off(); + } return firsterr; } -- cgit v1.2.3-59-g8ed1b From ab1b7880dec86bbdacd31a4c5cf104de4cf903f2 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 22 Sep 2020 16:42:42 -0700 Subject: rcutorture: Make stutter_wait() caller restore priority Currently, stutter_wait() will happily spin waiting for the stutter interval to end even if the caller is running at a real-time priority level. This could starve normal-priority tasks for no good reason. This commit therefore drops the calling task's priority to SCHED_OTHER MAX_NICE if stutter_wait() needs to wait. But when it waits, stutter_wait() returns true, which allows the caller to restore the priority if needed. Callers that were already running at SCHED_OTHER MAX_NICE obviously do not need any changes, but this commit also restores priority for higher-priority callers. Signed-off-by: Paul E. McKenney --- kernel/rcu/rcutorture.c | 24 ++++++++++++++++++------ kernel/torture.c | 9 ++++----- 2 files changed, 22 insertions(+), 11 deletions(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index db3767110c60..4391d2fab5de 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -912,7 +912,8 @@ static int rcu_torture_boost(void *arg) oldstarttime = boost_starttime; while (time_before(jiffies, oldstarttime)) { schedule_timeout_interruptible(oldstarttime - jiffies); - stutter_wait("rcu_torture_boost"); + if (stutter_wait("rcu_torture_boost")) + sched_set_fifo_low(current); if (torture_must_stop()) goto checkwait; } @@ -932,7 +933,8 @@ static int rcu_torture_boost(void *arg) jiffies); call_rcu_time = jiffies; } - stutter_wait("rcu_torture_boost"); + if (stutter_wait("rcu_torture_boost")) + sched_set_fifo_low(current); if (torture_must_stop()) goto checkwait; } @@ -964,7 +966,8 @@ static int rcu_torture_boost(void *arg) } /* Go do the stutter. */ -checkwait: stutter_wait("rcu_torture_boost"); +checkwait: if (stutter_wait("rcu_torture_boost")) + sched_set_fifo_low(current); } while (!torture_must_stop()); /* Clean up and exit. */ @@ -987,6 +990,7 @@ rcu_torture_fqs(void *arg) { unsigned long fqs_resume_time; int fqs_burst_remaining; + int oldnice = task_nice(current); VERBOSE_TOROUT_STRING("rcu_torture_fqs task started"); do { @@ -1002,7 +1006,8 @@ rcu_torture_fqs(void *arg) udelay(fqs_holdoff); fqs_burst_remaining -= fqs_holdoff; } - stutter_wait("rcu_torture_fqs"); + if (stutter_wait("rcu_torture_fqs")) + sched_set_normal(current, oldnice); } while (!torture_must_stop()); torture_kthread_stopping("rcu_torture_fqs"); return 0; @@ -1022,9 +1027,11 @@ rcu_torture_writer(void *arg) bool gp_cond1 = gp_cond, gp_exp1 = gp_exp, gp_normal1 = gp_normal; bool gp_sync1 = gp_sync; int i; + int oldnice = task_nice(current); struct rcu_torture *rp; struct rcu_torture *old_rp; static DEFINE_TORTURE_RANDOM(rand); + bool stutter_waited; int synctype[] = { RTWS_DEF_FREE, RTWS_EXP_SYNC, RTWS_COND_GET, RTWS_SYNC }; int nsynctypes = 0; @@ -1143,7 +1150,8 @@ rcu_torture_writer(void *arg) !rcu_gp_is_normal(); } rcu_torture_writer_state = RTWS_STUTTER; - if (stutter_wait("rcu_torture_writer") && + stutter_waited = stutter_wait("rcu_torture_writer"); + if (stutter_waited && !READ_ONCE(rcu_fwd_cb_nodelay) && !cur_ops->slow_gps && !torture_must_stop() && @@ -1155,6 +1163,8 @@ rcu_torture_writer(void *arg) rcu_ftrace_dump(DUMP_ALL); WARN(1, "%s: rtort_pipe_count: %d\n", __func__, rcu_tortures[i].rtort_pipe_count); } + if (stutter_waited) + sched_set_normal(current, oldnice); } while (!torture_must_stop()); rcu_torture_current = NULL; // Let stats task know that we are done. /* Reset expediting back to unexpedited. */ @@ -2103,6 +2113,7 @@ static struct notifier_block rcutorture_oom_nb = { /* Carry out grace-period forward-progress testing. */ static int rcu_torture_fwd_prog(void *args) { + int oldnice = task_nice(current); struct rcu_fwd *rfp = args; int tested = 0; int tested_tries = 0; @@ -2121,7 +2132,8 @@ static int rcu_torture_fwd_prog(void *args) rcu_torture_fwd_prog_cr(rfp); /* Avoid slow periods, better to test when busy. */ - stutter_wait("rcu_torture_fwd_prog"); + if (stutter_wait("rcu_torture_fwd_prog")) + sched_set_normal(current, oldnice); } while (!torture_must_stop()); /* Short runs might not contain a valid forward-progress attempt. */ WARN_ON(!tested && tested_tries >= 5); diff --git a/kernel/torture.c b/kernel/torture.c index 56ff02bf444f..8562ac18d2eb 100644 --- a/kernel/torture.c +++ b/kernel/torture.c @@ -604,19 +604,19 @@ bool stutter_wait(const char *title) { ktime_t delay; unsigned int i = 0; - int oldnice; bool ret = false; int spt; cond_resched_tasks_rcu_qs(); spt = READ_ONCE(stutter_pause_test); for (; spt; spt = READ_ONCE(stutter_pause_test)) { - ret = true; + if (!ret) { + sched_set_normal(current, MAX_NICE); + ret = true; + } if (spt == 1) { schedule_timeout_interruptible(1); } else if (spt == 2) { - oldnice = task_nice(current); - set_user_nice(current, MAX_NICE); while (READ_ONCE(stutter_pause_test)) { if (!(i++ & 0xffff)) { set_current_state(TASK_INTERRUPTIBLE); @@ -625,7 +625,6 @@ bool stutter_wait(const char *title) } cond_resched(); } - set_user_nice(current, oldnice); } else { schedule_timeout_interruptible(round_jiffies_relative(HZ)); } -- cgit v1.2.3-59-g8ed1b From 293b93d66f149a9bd124aae195f048268e11870c Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 23 Sep 2020 16:46:36 -0700 Subject: rcutorture: Small code cleanups The rcu_torture_cleanup() function fails to NULL out the reader_tasks pointer after freeing it and its fakewriter_tasks loop has redundant braces. This commit therefore cleans these up. Signed-off-by: Paul E. McKenney --- kernel/rcu/rcutorture.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index 4391d2fab5de..e7d52fded3cd 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -2496,13 +2496,13 @@ rcu_torture_cleanup(void) torture_stop_kthread(rcu_torture_reader, reader_tasks[i]); kfree(reader_tasks); + reader_tasks = NULL; } if (fakewriter_tasks) { - for (i = 0; i < nfakewriters; i++) { + for (i = 0; i < nfakewriters; i++) torture_stop_kthread(rcu_torture_fakewriter, fakewriter_tasks[i]); - } kfree(fakewriter_tasks); fakewriter_tasks = NULL; } -- cgit v1.2.3-59-g8ed1b From a7eb937b67b64b8b4645f1ebca3ac2079c6de81b Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 9 Oct 2020 19:51:55 -0700 Subject: rcutorture: Don't do need_resched() testing if ->sync is NULL If cur_ops->sync is NULL, rcu_torture_fwd_prog_nr() will nevertheless attempt to call through it. This commit therefore flags cases where neither need_resched() nor call_rcu() forward-progress testing can be performed due to NULL function pointers, and also causes rcu_torture_fwd_prog_nr() to take an early exit if cur_ops->sync() is NULL. Reported-by: Tom Rix Signed-off-by: Paul E. McKenney --- kernel/rcu/rcutorture.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index e7d52fded3cd..4dfd113882aa 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -1923,7 +1923,9 @@ static void rcu_torture_fwd_prog_nr(struct rcu_fwd *rfp, unsigned long stopat; static DEFINE_TORTURE_RANDOM(trs); - if (cur_ops->call && cur_ops->sync && cur_ops->cb_barrier) { + if (!cur_ops->sync) + return; // Cannot do need_resched() forward progress testing without ->sync. + if (cur_ops->call && cur_ops->cb_barrier) { init_rcu_head_on_stack(&fcs.rh); selfpropcb = true; } @@ -2149,8 +2151,8 @@ static int __init rcu_torture_fwd_prog_init(void) if (!fwd_progress) return 0; /* Not requested, so don't do it. */ - if (!cur_ops->stall_dur || cur_ops->stall_dur() <= 0 || - cur_ops == &rcu_busted_ops) { + if ((!cur_ops->sync && !cur_ops->call) || + !cur_ops->stall_dur || cur_ops->stall_dur() <= 0 || cur_ops == &rcu_busted_ops) { VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test"); return 0; } -- cgit v1.2.3-59-g8ed1b From 75dc2da5ecd65bdcbfc4d59b9d9b7342c61fe374 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 17 Sep 2020 16:17:17 -0700 Subject: rcu-tasks: Make the units of ->init_fract be jiffies Currently, the units of ->init_fract are milliseconds while those of ->gp_sleep are jiffies. For consistency with each other and with the argument of schedule_timeout_idle(), this commit changes the units of ->init_fract to jiffies. This change does affect the backoff algorithm, but only on systems where HZ is not 1000, and even there the change makes more sense, given that the current setup would "back off" to the same number of jiffies repeatedly. In contrast, with this change, the number of jiffies waited increases on each pass through the loop in the rcu_tasks_wait_gp() function. Signed-off-by: Paul E. McKenney --- kernel/rcu/tasks.h | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 0b459890fdcc..35bdcfd84d42 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -335,8 +335,6 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) // Start off with initial wait and slowly back off to 1 HZ wait. fract = rtp->init_fract; - if (fract > HZ) - fract = HZ; while (!list_empty(&holdouts)) { bool firstreport; @@ -345,10 +343,10 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) /* Slowly back off waiting for holdouts */ set_tasks_gp_state(rtp, RTGS_WAIT_SCAN_HOLDOUTS); - schedule_timeout_idle(HZ/fract); + schedule_timeout_idle(fract); - if (fract > 1) - fract--; + if (fract < HZ) + fract++; rtst = READ_ONCE(rcu_task_stall_timeout); needreport = rtst > 0 && time_after(jiffies, lastreport + rtst); @@ -557,7 +555,7 @@ EXPORT_SYMBOL_GPL(rcu_barrier_tasks); static int __init rcu_spawn_tasks_kthread(void) { rcu_tasks.gp_sleep = HZ / 10; - rcu_tasks.init_fract = 10; + rcu_tasks.init_fract = HZ / 10; rcu_tasks.pregp_func = rcu_tasks_pregp_step; rcu_tasks.pertask_func = rcu_tasks_pertask; rcu_tasks.postscan_func = rcu_tasks_postscan; @@ -1178,12 +1176,12 @@ static int __init rcu_spawn_tasks_trace_kthread(void) { if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) { rcu_tasks_trace.gp_sleep = HZ / 10; - rcu_tasks_trace.init_fract = 10; + rcu_tasks_trace.init_fract = HZ / 10; } else { rcu_tasks_trace.gp_sleep = HZ / 200; if (rcu_tasks_trace.gp_sleep <= 0) rcu_tasks_trace.gp_sleep = 1; - rcu_tasks_trace.init_fract = HZ / 5; + rcu_tasks_trace.init_fract = HZ / 200; if (rcu_tasks_trace.init_fract <= 0) rcu_tasks_trace.init_fract = 1; } -- cgit v1.2.3-59-g8ed1b From 6dbce04d8417ae706596366e16841d77c454ba52 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 16 Nov 2020 13:10:12 +0100 Subject: rcu: Allow rcu_irq_enter_check_tick() from NMI MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Eugenio managed to tickle #PF from NMI context which resulted in hitting a WARN in RCU through irqentry_enter() -> __rcu_irq_enter_check_tick(). However, this situation is perfectly sane and does not warrant an WARN. The #PF will (necessarily) be atomic and not require messing with the tick state, so early return is correct. This commit therefore removes the WARN. Fixes: aaf2bc50df1f ("rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter()") Reported-by: "Eugenio Pérez" Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Andy Lutomirski Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 06895ef85d69..93e1808ac3fc 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -928,8 +928,8 @@ void __rcu_irq_enter_check_tick(void) { struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - // Enabling the tick is unsafe in NMI handlers. - if (WARN_ON_ONCE(in_nmi())) + // If we're here from NMI there's nothing to do. + if (in_nmi()) return; RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(), -- cgit v1.2.3-59-g8ed1b From dfe564045c653d9e6969ccca57a8a04771d333f7 Mon Sep 17 00:00:00 2001 From: chao Date: Sun, 30 Aug 2020 23:41:17 -0700 Subject: rcu: Panic after fixed number of stalls Some stalls are transient, so that system fully recovers. This commit therefore allows users to configure the number of stalls that must happen in order to trigger kernel panic. Signed-off-by: chao Signed-off-by: Paul E. McKenney --- include/linux/kernel.h | 1 + kernel/rcu/tree_stall.h | 6 ++++++ kernel/sysctl.c | 11 +++++++++++ 3 files changed, 18 insertions(+) (limited to 'kernel/rcu') diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 2f05e9128201..4b5fd3da5fe8 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -536,6 +536,7 @@ extern int panic_on_warn; extern unsigned long panic_on_taint; extern bool panic_on_taint_nousertaint; extern int sysctl_panic_on_rcu_stall; +extern int sysctl_max_rcu_stall_to_panic; extern int sysctl_panic_on_stackoverflow; extern bool crash_kexec_post_notifiers; diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index ca21d28a0f98..70d48c52fabc 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -13,6 +13,7 @@ /* panic() on RCU Stall sysctl. */ int sysctl_panic_on_rcu_stall __read_mostly; +int sysctl_max_rcu_stall_to_panic __read_mostly; #ifdef CONFIG_PROVE_RCU #define RCU_STALL_DELAY_DELTA (5 * HZ) @@ -106,6 +107,11 @@ early_initcall(check_cpu_stall_init); /* If so specified via sysctl, panic, yielding cleaner stall-warning output. */ static void panic_on_rcu_stall(void) { + static int cpu_stall; + + if (++cpu_stall < sysctl_max_rcu_stall_to_panic) + return; + if (sysctl_panic_on_rcu_stall) panic("RCU Stall\n"); } diff --git a/kernel/sysctl.c b/kernel/sysctl.c index afad085960b8..c9fbdd848138 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -2650,6 +2650,17 @@ static struct ctl_table kern_table[] = { .extra2 = SYSCTL_ONE, }, #endif +#if defined(CONFIG_TREE_RCU) + { + .procname = "max_rcu_stall_to_panic", + .data = &sysctl_max_rcu_stall_to_panic, + .maxlen = sizeof(sysctl_max_rcu_stall_to_panic), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = SYSCTL_ONE, + .extra2 = SYSCTL_INT_MAX, + }, +#endif #ifdef CONFIG_STACKLEAK_RUNTIME_DISABLE { .procname = "stack_erasing", -- cgit v1.2.3-59-g8ed1b From e3771c850d3b9349b48449c9a91c98944a08650c Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Mon, 21 Sep 2020 14:43:40 +0200 Subject: rcu: Implement rcu_segcblist_is_offloaded() config dependent This commit simplifies the use of the rcu_segcblist_is_offloaded() API so that its callers no longer need to check the RCU_NOCB_CPU Kconfig option. Note that rcu_segcblist_is_offloaded() is defined in the header file, which means that the generated code should be just as efficient as before. Suggested-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: Paul E. McKenney Cc: Josh Triplett Cc: Steven Rostedt Cc: Mathieu Desnoyers Cc: Lai Jiangshan Cc: Joel Fernandes Signed-off-by: Paul E. McKenney --- kernel/rcu/rcu_segcblist.h | 2 +- kernel/rcu/tree.c | 21 +++++++-------------- 2 files changed, 8 insertions(+), 15 deletions(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h index 5c293afc07b8..492262bcb591 100644 --- a/kernel/rcu/rcu_segcblist.h +++ b/kernel/rcu/rcu_segcblist.h @@ -62,7 +62,7 @@ static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp) /* Is the specified rcu_segcblist offloaded? */ static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp) { - return rsclp->offloaded; + return IS_ENABLED(CONFIG_RCU_NOCB_CPU) && rsclp->offloaded; } /* diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 93e1808ac3fc..0ccdca441ddf 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1603,8 +1603,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) { bool ret = false; bool need_qs; - const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) && - rcu_segcblist_is_offloaded(&rdp->cblist); + const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); raw_lockdep_assert_held_rcu_node(rnp); @@ -2048,8 +2047,7 @@ static void rcu_gp_cleanup(void) needgp = true; } /* Advance CBs to reduce false positives below. */ - offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) && - rcu_segcblist_is_offloaded(&rdp->cblist); + offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) { WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT); WRITE_ONCE(rcu_state.gp_req_activity, jiffies); @@ -2248,8 +2246,7 @@ rcu_report_qs_rdp(struct rcu_data *rdp) unsigned long flags; unsigned long mask; bool needwake = false; - const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) && - rcu_segcblist_is_offloaded(&rdp->cblist); + const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); struct rcu_node *rnp; WARN_ON_ONCE(rdp->cpu != smp_processor_id()); @@ -2417,8 +2414,7 @@ static void rcu_do_batch(struct rcu_data *rdp) { int div; unsigned long flags; - const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) && - rcu_segcblist_is_offloaded(&rdp->cblist); + const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); struct rcu_head *rhp; struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl); long bl, count; @@ -2675,8 +2671,7 @@ static __latent_entropy void rcu_core(void) unsigned long flags; struct rcu_data *rdp = raw_cpu_ptr(&rcu_data); struct rcu_node *rnp = rdp->mynode; - const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) && - rcu_segcblist_is_offloaded(&rdp->cblist); + const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); if (cpu_is_offline(smp_processor_id())) return; @@ -2978,8 +2973,7 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func) rcu_segcblist_n_cbs(&rdp->cblist)); /* Go handle any RCU core processing required. */ - if (IS_ENABLED(CONFIG_RCU_NOCB_CPU) && - unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) { + if (unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) { __call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */ } else { __call_rcu_core(rdp, head, flags); @@ -3712,8 +3706,7 @@ static int rcu_pending(int user) /* Has RCU gone idle with this CPU needing another grace period? */ if (!gp_in_progress && rcu_segcblist_is_enabled(&rdp->cblist) && - (!IS_ENABLED(CONFIG_RCU_NOCB_CPU) || - !rcu_segcblist_is_offloaded(&rdp->cblist)) && + !rcu_segcblist_is_offloaded(&rdp->cblist) && !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) return 1; -- cgit v1.2.3-59-g8ed1b From ed73860cecc3ec12aa50a6dcfb4900e5b4ae9507 Mon Sep 17 00:00:00 2001 From: Neeraj Upadhyay Date: Wed, 23 Sep 2020 12:59:33 +0530 Subject: rcu: Fix single-CPU check in rcu_blocking_is_gp() Currently, for CONFIG_PREEMPTION=n kernels, rcu_blocking_is_gp() uses num_online_cpus() to determine whether there is only one CPU online. When there is only a single CPU online, the simple fact that synchronize_rcu() could be legally called implies that a full grace period has elapsed. Therefore, in the single-CPU case, synchronize_rcu() simply returns immediately. Unfortunately, num_online_cpus() is unreliable while a CPU-hotplug operation is transitioning to or from single-CPU operation because: 1. num_online_cpus() uses atomic_read(&__num_online_cpus) to locklessly sample the number of online CPUs. The hotplug locks are not held, which means that an incoming CPU can concurrently update this count. This in turn means that an RCU read-side critical section on the incoming CPU might observe updates prior to the grace period, but also that this critical section might extend beyond the end of the optimized synchronize_rcu(). This breaks RCU's fundamental guarantee. 2. In addition, num_online_cpus() does no ordering, thus providing another way that RCU's fundamental guarantee can be broken by the current code. 3. The most probable failure mode happens on outgoing CPUs. The outgoing CPU updates the count of online CPUs in the CPUHP_TEARDOWN_CPU stop-machine handler, which is fine in and of itself due to preemption being disabled at the call to num_online_cpus(). Unfortunately, after that stop-machine handler returns, the CPU takes one last trip through the scheduler (which has RCU readers) and, after the resulting context switch, one final dive into the idle loop. During this time, RCU needs to keep track of two CPUs, but num_online_cpus() will say that there is only one, which in turn means that the surviving CPU will incorrectly ignore the outgoing CPU's RCU read-side critical sections. This problem is illustrated by the following litmus test in which P0() corresponds to synchronize_rcu() and P1() corresponds to the incoming CPU. The herd7 tool confirms that the "exists" clause can be satisfied, thus demonstrating that this breakage can happen according to the Linux kernel memory model. { int x = 0; atomic_t numonline = ATOMIC_INIT(1); } P0(int *x, atomic_t *numonline) { int r0; WRITE_ONCE(*x, 1); r0 = atomic_read(numonline); if (r0 == 1) { smp_mb(); } else { synchronize_rcu(); } WRITE_ONCE(*x, 2); } P1(int *x, atomic_t *numonline) { int r0; int r1; atomic_inc(numonline); smp_mb(); rcu_read_lock(); r0 = READ_ONCE(*x); smp_rmb(); r1 = READ_ONCE(*x); rcu_read_unlock(); } locations [x;numonline;] exists (1:r0=0 /\ 1:r1=2) It is important to note that these problems arise only when the system is transitioning to or from single-CPU operation. One solution would be to hold the CPU-hotplug locks while sampling num_online_cpus(), which was in fact the intent of the (redundant) preempt_disable() and preempt_enable() surrounding this call to num_online_cpus(). Actually blocking CPU hotplug would not only result in excessive overhead, but would also unnecessarily impede CPU-hotplug operations. This commit therefore follows long-standing RCU tradition by maintaining a separate RCU-specific set of CPU-hotplug books. This separate set of books is implemented by a new ->n_online_cpus field in the rcu_state structure that maintains RCU's count of the online CPUs. This count is incremented early in the CPU-online process, so that the critical transition away from single-CPU operation will occur when there is only a single CPU. Similarly for the critical transition to single-CPU operation, the counter is decremented late in the CPU-offline process, again while there is only a single CPU. Because there is only ever a single CPU when the ->n_online_cpus field undergoes the critical 1->2 and 2->1 transitions, full memory ordering and mutual exclusion is provided implicitly and, better yet, for free. In the case where the CPU is coming online, nothing will happen until the current CPU helps it come online. Therefore, the new CPU will see all accesses prior to the optimized grace period, which means that RCU does not need to further delay this new CPU. In the case where the CPU is going offline, the outgoing CPU is totally out of the picture before the optimized grace period starts, which means that this outgoing CPU cannot see any of the accesses following that grace period. Again, RCU needs no further interaction with the outgoing CPU. This does mean that synchronize_rcu() will unnecessarily do a few grace periods the hard way just before the second CPU comes online and just after the second-to-last CPU goes offline, but it is not worth optimizing this uncommon case. Reviewed-by: Joel Fernandes (Google) Signed-off-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 19 +++++++++++++++++-- kernel/rcu/tree.h | 1 + 2 files changed, 18 insertions(+), 2 deletions(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 0ccdca441ddf..39e14cf6a9c0 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2396,6 +2396,7 @@ int rcutree_dead_cpu(unsigned int cpu) if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) return 0; + WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1); /* Adjust any no-longer-needed kthreads. */ rcu_boost_kthread_setaffinity(rnp, -1); /* Do any needed no-CB deferred wakeups from this CPU. */ @@ -3577,7 +3578,20 @@ static int rcu_blocking_is_gp(void) return rcu_scheduler_active == RCU_SCHEDULER_INACTIVE; might_sleep(); /* Check for RCU read-side critical section. */ preempt_disable(); - ret = num_online_cpus() <= 1; + /* + * If the rcu_state.n_online_cpus counter is equal to one, + * there is only one CPU, and that CPU sees all prior accesses + * made by any CPU that was online at the time of its access. + * Furthermore, if this counter is equal to one, its value cannot + * change until after the preempt_enable() below. + * + * Furthermore, if rcu_state.n_online_cpus is equal to one here, + * all later CPUs (both this one and any that come online later + * on) are guaranteed to see all accesses prior to this point + * in the code, without the need for additional memory barriers. + * Those memory barriers are provided by CPU-hotplug code. + */ + ret = READ_ONCE(rcu_state.n_online_cpus) <= 1; preempt_enable(); return ret; } @@ -3622,7 +3636,7 @@ void synchronize_rcu(void) lock_is_held(&rcu_sched_lock_map), "Illegal synchronize_rcu() in RCU read-side critical section"); if (rcu_blocking_is_gp()) - return; + return; // Context allows vacuous grace periods. if (rcu_gp_is_expedited()) synchronize_rcu_expedited(); else @@ -3962,6 +3976,7 @@ int rcutree_prepare_cpu(unsigned int cpu) raw_spin_unlock_irqrestore_rcu_node(rnp, flags); rcu_prepare_kthreads(cpu); rcu_spawn_cpu_nocb_kthread(cpu); + WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus + 1); return 0; } diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index e4f66b8f7c47..805c9eb6f7ae 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -298,6 +298,7 @@ struct rcu_state { /* Hierarchy levels (+1 to */ /* shut bogus gcc warning) */ int ncpus; /* # CPUs seen so far. */ + int n_online_cpus; /* # CPUs online for RCU. */ /* The following fields are guarded by the root rcu_node's lock. */ -- cgit v1.2.3-59-g8ed1b From a3941517fcd6625adc540aef5ec3f717c8fa71e8 Mon Sep 17 00:00:00 2001 From: Neeraj Upadhyay Date: Thu, 24 Sep 2020 12:04:10 +0530 Subject: rcu: Clarify nocb kthreads naming in RCU_NOCB_CPU config This commit clarifies that the "p" and the "s" in the in the RCU_NOCB_CPU config-option description refer to the "x" in the "rcuox/N" kthread name. Signed-off-by: Neeraj Upadhyay [ paulmck: While in the area, update description and advice. ] Signed-off-by: Paul E. McKenney --- kernel/rcu/Kconfig | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index b71e21f73c40..cdc57b4f6d48 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -221,19 +221,23 @@ config RCU_NOCB_CPU Use this option to reduce OS jitter for aggressive HPC or real-time workloads. It can also be used to offload RCU callback invocation to energy-efficient CPUs in battery-powered - asymmetric multiprocessors. + asymmetric multiprocessors. The price of this reduced jitter + is that the overhead of call_rcu() increases and that some + workloads will incur significant increases in context-switch + rates. This option offloads callback invocation from the set of CPUs specified at boot time by the rcu_nocbs parameter. For each such CPU, a kthread ("rcuox/N") will be created to invoke callbacks, where the "N" is the CPU being offloaded, and where - the "p" for RCU-preempt (PREEMPTION kernels) and "s" for RCU-sched - (!PREEMPTION kernels). Nothing prevents this kthread from running - on the specified CPUs, but (1) the kthreads may be preempted - between each callback, and (2) affinity or cgroups can be used - to force the kthreads to run on whatever set of CPUs is desired. - - Say Y here if you want to help to debug reduced OS jitter. + the "x" is "p" for RCU-preempt (PREEMPTION kernels) and "s" for + RCU-sched (!PREEMPTION kernels). Nothing prevents this kthread + from running on the specified CPUs, but (1) the kthreads may be + preempted between each callback, and (2) affinity or cgroups can + be used to force the kthreads to run on whatever set of CPUs is + desired. + + Say Y here if you need reduced OS jitter, despite added overhead. Say N here if you are unsure. config TASKS_TRACE_RCU_READ_MB -- cgit v1.2.3-59-g8ed1b From 9f866dac94292f93d3b6bf8dbe860a44b954e555 Mon Sep 17 00:00:00 2001 From: "Joel Fernandes (Google)" Date: Tue, 29 Sep 2020 15:29:27 -0400 Subject: rcu/tree: Add a warning if CPU being onlined did not report QS already Currently, rcu_cpu_starting() checks to see if the RCU core expects a quiescent state from the incoming CPU. However, the current interaction between RCU quiescent-state reporting and CPU-hotplug operations should mean that the incoming CPU never needs to report a quiescent state. First, the outgoing CPU reports a quiescent state if needed. Second, the race where the CPU is leaving just as RCU is initializing a new grace period is handled by an explicit check for this condition. Third, the CPU's leaf rcu_node structure's ->lock serializes these checks. This means that if rcu_cpu_starting() ever feels the need to report a quiescent state, then there is a bug somewhere in the CPU hotplug code or the RCU grace-period handling code. This commit therefore adds a WARN_ON_ONCE() to bring that bug to everyone's attention. Cc: Neeraj Upadhyay Suggested-by: Paul E. McKenney Signed-off-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 39e14cf6a9c0..e4d6d0b1b853 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -4075,7 +4075,9 @@ void rcu_cpu_starting(unsigned int cpu) rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */ rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq); rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags); - if (rnp->qsmask & mask) { /* RCU waiting on incoming CPU? */ + + /* An incoming CPU should never be blocking a grace period. */ + if (WARN_ON_ONCE(rnp->qsmask & mask)) { /* RCU waiting on incoming CPU? */ rcu_disable_urgency_upon_qs(rdp); /* Report QS -after- changing ->qsmaskinitnext! */ rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); -- cgit v1.2.3-59-g8ed1b From 7c47ee5aa00817d8b10f415b4a92d5fb3ac35273 Mon Sep 17 00:00:00 2001 From: Joe Perches Date: Sat, 3 Oct 2020 17:18:08 -0700 Subject: rcu/tree: Make struct kernel_param_ops definitions const These should be const, so make it so. Signed-off-by: Joe Perches Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e4d6d0b1b853..5f458e4efc95 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -546,12 +546,12 @@ static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param return ret; } -static struct kernel_param_ops first_fqs_jiffies_ops = { +static const struct kernel_param_ops first_fqs_jiffies_ops = { .set = param_set_first_fqs_jiffies, .get = param_get_ulong, }; -static struct kernel_param_ops next_fqs_jiffies_ops = { +static const struct kernel_param_ops next_fqs_jiffies_ops = { .set = param_set_next_fqs_jiffies, .get = param_get_ulong, }; -- cgit v1.2.3-59-g8ed1b From d2098b4440981705e844c50254540ba7b5f82795 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 29 Sep 2020 13:33:40 +0200 Subject: rcu,ftrace: Fix ftrace recursion Kim reported that perf-ftrace made his box unhappy. It turns out that commit: ff5c4f5cad33 ("rcu/tree: Mark the idle relevant functions noinstr") removed one too many notrace qualifiers, probably due to there not being a helpful comment. This commit therefore reinstates the notrace and adds a comment to avoid losing it again. [ paulmck: Apply Steven Rostedt's feedback on the comment. ] Fixes: ff5c4f5cad33 ("rcu/tree: Mark the idle relevant functions noinstr") Reported-by: Kim Phillips Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 5f458e4efc95..d6a015e68649 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1093,8 +1093,11 @@ static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp) * CPU can safely enter RCU read-side critical sections. In other words, * if the current CPU is not in its idle loop or is in an interrupt or * NMI handler, return true. + * + * Make notrace because it can be called by the internal functions of + * ftrace, and making this notrace removes unnecessary recursion calls. */ -bool rcu_is_watching(void) +notrace bool rcu_is_watching(void) { bool ret; -- cgit v1.2.3-59-g8ed1b From bd56e0a4a291bc9db2cbaddef20ec61a1aad4208 Mon Sep 17 00:00:00 2001 From: "Joel Fernandes (Google)" Date: Wed, 7 Oct 2020 13:50:36 -0700 Subject: rcu/tree: nocb: Avoid raising softirq for offloaded ready-to-execute CBs Testing showed that rcu_pending() can return 1 when offloaded callbacks are ready to execute. This invokes RCU core processing, for example, by raising RCU_SOFTIRQ, eventually resulting in a call to rcu_core(). However, rcu_core() explicitly avoids in any way manipulating offloaded callbacks, which are instead handled by the rcuog and rcuoc kthreads, which work independently of rcu_core(). One exception to this independence is that rcu_core() invokes do_nocb_deferred_wakeup(), however, rcu_pending() also checks rcu_nocb_need_deferred_wakeup() in order to correctly handle this case, invoking rcu_core() when needed. This commit therefore avoids needlessly invoking RCU core processing by checking rcu_segcblist_ready_cbs() only on non-offloaded CPUs. This reduces overhead, for example, by reducing softirq activity. This change passed 30 minute tests of TREE01 through TREE09 each. On TREE08, there is at most 150us from the time that rcu_pending() chose not to invoke RCU core processing to the time when the ready callbacks were invoked by the rcuoc kthread. This provides further evidence that there is no need to invoke rcu_core() for offloaded callbacks that are ready to invoke. Cc: Neeraj Upadhyay Reviewed-by: Frederic Weisbecker Reviewed-by: Neeraj Upadhyay Signed-off-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index d6a015e68649..50d90ee6dfe1 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3718,7 +3718,8 @@ static int rcu_pending(int user) return 1; /* Does this CPU have callbacks ready to invoke? */ - if (rcu_segcblist_ready_cbs(&rdp->cblist)) + if (!rcu_segcblist_is_offloaded(&rdp->cblist) && + rcu_segcblist_ready_cbs(&rdp->cblist)) return 1; /* Has RCU gone idle with this CPU needing another grace period? */ -- cgit v1.2.3-59-g8ed1b From 4d60b475f858ebdb06c1339f01a890f287b5e587 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 13 Oct 2020 12:39:23 -0700 Subject: rcu: Prevent lockdep-RCU splats on lock acquisition/release The rcu_cpu_starting() and rcu_report_dead() functions transition the current CPU between online and offline state from an RCU perspective. Unfortunately, this means that the rcu_cpu_starting() function's lock acquisition and the rcu_report_dead() function's lock releases happen while the CPU is offline from an RCU perspective, which can result in lockdep-RCU splats about using RCU from an offline CPU. And this situation can also result in too-short grace periods, especially in guest OSes that are subject to vCPU preemption. This commit therefore uses sequence-count-like synchronization to forgive use of RCU while RCU thinks a CPU is offline across the full extent of the rcu_cpu_starting() and rcu_report_dead() function's lock acquisitions and releases. One approach would have been to use the actual sequence-count primitives provided by the Linux kernel. Unfortunately, the resulting code looks completely broken and wrong, and is likely to result in patches that break RCU in an attempt to address this appearance of broken wrongness. Plus there is no net savings in lines of code, given the additional explicit memory barriers required. Therefore, this sequence count is instead implemented by a new ->ofl_seq field in the rcu_node structure. If this counter's value is an odd number, RCU forgives RCU read-side critical sections on other CPUs covered by the same rcu_node structure, even if those CPUs are offline from an RCU perspective. In addition, if a given leaf rcu_node structure's ->ofl_seq counter value is an odd number, rcu_gp_init() delays starting the grace period until that counter value changes. [ paulmck: Apply Peter Zijlstra feedback. ] Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 21 ++++++++++++++++++++- kernel/rcu/tree.h | 1 + 2 files changed, 21 insertions(+), 1 deletion(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 50d90ee6dfe1..34385341f66a 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1152,7 +1152,7 @@ bool rcu_lockdep_current_cpu_online(void) preempt_disable_notrace(); rdp = this_cpu_ptr(&rcu_data); rnp = rdp->mynode; - if (rdp->grpmask & rcu_rnp_online_cpus(rnp)) + if (rdp->grpmask & rcu_rnp_online_cpus(rnp) || READ_ONCE(rnp->ofl_seq) & 0x1) ret = true; preempt_enable_notrace(); return ret; @@ -1717,6 +1717,7 @@ static void rcu_strict_gp_boundary(void *unused) */ static bool rcu_gp_init(void) { + unsigned long firstseq; unsigned long flags; unsigned long oldmask; unsigned long mask; @@ -1760,6 +1761,12 @@ static bool rcu_gp_init(void) */ rcu_state.gp_state = RCU_GP_ONOFF; rcu_for_each_leaf_node(rnp) { + smp_mb(); // Pair with barriers used when updating ->ofl_seq to odd values. + firstseq = READ_ONCE(rnp->ofl_seq); + if (firstseq & 0x1) + while (firstseq == READ_ONCE(rnp->ofl_seq)) + schedule_timeout_idle(1); // Can't wake unless RCU is watching. + smp_mb(); // Pair with barriers used when updating ->ofl_seq to even values. raw_spin_lock(&rcu_state.ofl_lock); raw_spin_lock_irq_rcu_node(rnp); if (rnp->qsmaskinit == rnp->qsmaskinitnext && @@ -4069,6 +4076,9 @@ void rcu_cpu_starting(unsigned int cpu) rnp = rdp->mynode; mask = rdp->grpmask; + WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1); + WARN_ON_ONCE(!(rnp->ofl_seq & 0x1)); + smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier(). raw_spin_lock_irqsave_rcu_node(rnp, flags); WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask); newcpu = !(rnp->expmaskinitnext & mask); @@ -4088,6 +4098,9 @@ void rcu_cpu_starting(unsigned int cpu) } else { raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } + smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier(). + WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1); + WARN_ON_ONCE(rnp->ofl_seq & 0x1); smp_mb(); /* Ensure RCU read-side usage follows above initialization. */ } @@ -4115,6 +4128,9 @@ void rcu_report_dead(unsigned int cpu) /* Remove outgoing CPU from mask in the leaf rcu_node structure. */ mask = rdp->grpmask; + WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1); + WARN_ON_ONCE(!(rnp->ofl_seq & 0x1)); + smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier(). raw_spin_lock(&rcu_state.ofl_lock); raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */ rdp->rcu_ofl_gp_seq = READ_ONCE(rcu_state.gp_seq); @@ -4127,6 +4143,9 @@ void rcu_report_dead(unsigned int cpu) WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext & ~mask); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); raw_spin_unlock(&rcu_state.ofl_lock); + smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier(). + WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1); + WARN_ON_ONCE(rnp->ofl_seq & 0x1); rdp->cpu_started = false; } diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 805c9eb6f7ae..7708ed161f4a 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -56,6 +56,7 @@ struct rcu_node { /* Initialized from ->qsmaskinitnext at the */ /* beginning of each grace period. */ unsigned long qsmaskinitnext; + unsigned long ofl_seq; /* CPU-hotplug operation sequence count. */ /* Online CPUs for next grace period. */ unsigned long expmask; /* CPUs or groups that need to check in */ /* to allow the current expedited GP */ -- cgit v1.2.3-59-g8ed1b From 354c3f0e22dcb17c10d0b79f6e1c5ba286eec0b0 Mon Sep 17 00:00:00 2001 From: Zhouyi Zhou Date: Thu, 15 Oct 2020 03:53:03 +0000 Subject: rcu: Fix a typo in rcu_blocking_is_gp() header comment This commit fixes a typo in the rcu_blocking_is_gp() function's header comment. Signed-off-by: Zhouyi Zhou Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 34385341f66a..0f278d6486c2 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3572,7 +3572,7 @@ void __init kfree_rcu_scheduler_running(void) * During early boot, any blocking grace-period wait automatically * implies a grace period. Later on, this is never the case for PREEMPTION. * - * Howevr, because a context switch is a grace period for !PREEMPTION, any + * However, because a context switch is a grace period for !PREEMPTION, any * blocking grace-period wait automatically implies a grace period if * there is only one CPU online at any point time during execution of * either synchronize_rcu() or synchronize_rcu_expedited(). It is OK to -- cgit v1.2.3-59-g8ed1b From bfb3aa735f82c8d98b32a669934ee7d6b346264d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 30 Oct 2020 13:11:24 -0700 Subject: rcu: Do not report strict GPs for outgoing CPUs An outgoing CPU is marked offline in a stop-machine handler and most of that CPU's services stop at that point, including IRQ work queues. However, that CPU must take another pass through the scheduler and through a number of CPU-hotplug notifiers, many of which contain RCU readers. In the past, these readers were not a problem because the outgoing CPU has interrupts disabled, so that rcu_read_unlock_special() would not be invoked, and thus RCU would never attempt to queue IRQ work on the outgoing CPU. This changed with the advent of the CONFIG_RCU_STRICT_GRACE_PERIOD Kconfig option, in which rcu_read_unlock_special() is invoked upon exit from almost all RCU read-side critical sections. Worse yet, because interrupts are disabled, rcu_read_unlock_special() cannot immediately report a quiescent state and will therefore attempt to defer this reporting, for example, by queueing IRQ work. Which fails with a splat because the CPU is already marked as being offline. But it turns out that there is no need to report this quiescent state because rcu_report_dead() will do this job shortly after the outgoing CPU makes its final dive into the idle loop. This commit therefore makes rcu_read_unlock_special() refrain from queuing IRQ work onto outgoing CPUs. Fixes: 44bad5b3cca2 ("rcu: Do full report for .need_qs for strict GPs") Signed-off-by: Paul E. McKenney Cc: Jann Horn --- kernel/rcu/tree_plugin.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index fd8a52e9a887..7e291ce0a1d6 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -628,7 +628,7 @@ static void rcu_read_unlock_special(struct task_struct *t) set_tsk_need_resched(current); set_preempt_need_resched(); if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled && - !rdp->defer_qs_iw_pending && exp) { + !rdp->defer_qs_iw_pending && exp && cpu_online(rdp->cpu)) { // Get scheduler to re-evaluate and call hooks. // If !IRQ_WORK, FQS scan will eventually IPI. init_irq_work(&rdp->defer_qs_iw, -- cgit v1.2.3-59-g8ed1b From 56292e8609e39537297a7468dda4d87b9bd81d6a Mon Sep 17 00:00:00 2001 From: "Uladzislau Rezki (Sony)" Date: Thu, 29 Oct 2020 17:50:04 +0100 Subject: rcu/tree: Defer kvfree_rcu() allocation to a clean context The current memmory-allocation interface causes the following difficulties for kvfree_rcu(): a) If built with CONFIG_PROVE_RAW_LOCK_NESTING, the lockdep will complain about violation of the nesting rules, as in "BUG: Invalid wait context". This Kconfig option checks for proper raw_spinlock vs. spinlock nesting, in particular, it is not legal to acquire a spinlock_t while holding a raw_spinlock_t. This is a problem because kfree_rcu() uses raw_spinlock_t whereas the "page allocator" internally deals with spinlock_t to access to its zones. The code also can be broken from higher level of view: raw_spin_lock(&some_lock); kfree_rcu(some_pointer, some_field_offset); b) If built with CONFIG_PREEMPT_RT, spinlock_t is converted into sleeplock. This means that invoking the page allocator from atomic contexts results in "BUG: scheduling while atomic". c) Please note that call_rcu() is already invoked from raw atomic context, so it is only reasonable to expaect that kfree_rcu() and kvfree_rcu() will also be called from atomic raw context. This commit therefore defers page allocation to a clean context using the combination of an hrtimer and a workqueue. The hrtimer stage is required in order to avoid deadlocks with the scheduler. This deferred allocation is required only when kvfree_rcu()'s per-CPU page cache is empty. Link: https://lore.kernel.org/lkml/20200630164543.4mdcf6zb4zfclhln@linutronix.de/ Fixes: 3042f83f19be ("rcu: Support reclaim for head-less object") Reported-by: Sebastian Andrzej Siewior Signed-off-by: Uladzislau Rezki (Sony) Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 109 +++++++++++++++++++++++++++++++++--------------------- 1 file changed, 66 insertions(+), 43 deletions(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 0f278d6486c2..01918d8cffb3 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -177,7 +177,7 @@ module_param(rcu_unlock_delay, int, 0444); * per-CPU. Object size is equal to one page. This value * can be changed at boot time. */ -static int rcu_min_cached_objs = 2; +static int rcu_min_cached_objs = 5; module_param(rcu_min_cached_objs, int, 0444); /* Retrieve RCU kthreads priority for rcutorture */ @@ -3089,6 +3089,9 @@ struct kfree_rcu_cpu_work { * In order to save some per-cpu space the list is singular. * Even though it is lockless an access has to be protected by the * per-cpu lock. + * @page_cache_work: A work to refill the cache when it is empty + * @work_in_progress: Indicates that page_cache_work is running + * @hrtimer: A hrtimer for scheduling a page_cache_work * @nr_bkv_objs: number of allocated objects at @bkvcache. * * This is a per-CPU structure. The reason that it is not included in @@ -3105,6 +3108,11 @@ struct kfree_rcu_cpu { bool monitor_todo; bool initialized; int count; + + struct work_struct page_cache_work; + atomic_t work_in_progress; + struct hrtimer hrtimer; + struct llist_head bkvcache; int nr_bkv_objs; }; @@ -3222,10 +3230,10 @@ static void kfree_rcu_work(struct work_struct *work) } rcu_lock_release(&rcu_callback_map); - krcp = krc_this_cpu_lock(&flags); + raw_spin_lock_irqsave(&krcp->lock, flags); if (put_cached_bnode(krcp, bkvhead[i])) bkvhead[i] = NULL; - krc_this_cpu_unlock(krcp, flags); + raw_spin_unlock_irqrestore(&krcp->lock, flags); if (bkvhead[i]) free_page((unsigned long) bkvhead[i]); @@ -3352,6 +3360,57 @@ static void kfree_rcu_monitor(struct work_struct *work) raw_spin_unlock_irqrestore(&krcp->lock, flags); } +static enum hrtimer_restart +schedule_page_work_fn(struct hrtimer *t) +{ + struct kfree_rcu_cpu *krcp = + container_of(t, struct kfree_rcu_cpu, hrtimer); + + queue_work(system_highpri_wq, &krcp->page_cache_work); + return HRTIMER_NORESTART; +} + +static void fill_page_cache_func(struct work_struct *work) +{ + struct kvfree_rcu_bulk_data *bnode; + struct kfree_rcu_cpu *krcp = + container_of(work, struct kfree_rcu_cpu, + page_cache_work); + unsigned long flags; + bool pushed; + int i; + + for (i = 0; i < rcu_min_cached_objs; i++) { + bnode = (struct kvfree_rcu_bulk_data *) + __get_free_page(GFP_KERNEL | __GFP_NOWARN); + + if (bnode) { + raw_spin_lock_irqsave(&krcp->lock, flags); + pushed = put_cached_bnode(krcp, bnode); + raw_spin_unlock_irqrestore(&krcp->lock, flags); + + if (!pushed) { + free_page((unsigned long) bnode); + break; + } + } + } + + atomic_set(&krcp->work_in_progress, 0); +} + +static void +run_page_cache_worker(struct kfree_rcu_cpu *krcp) +{ + if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING && + !atomic_xchg(&krcp->work_in_progress, 1)) { + hrtimer_init(&krcp->hrtimer, CLOCK_MONOTONIC, + HRTIMER_MODE_REL); + krcp->hrtimer.function = schedule_page_work_fn; + hrtimer_start(&krcp->hrtimer, 0, HRTIMER_MODE_REL); + } +} + static inline bool kvfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cpu *krcp, void *ptr) { @@ -3368,32 +3427,8 @@ kvfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cpu *krcp, void *ptr) if (!krcp->bkvhead[idx] || krcp->bkvhead[idx]->nr_records == KVFREE_BULK_MAX_ENTR) { bnode = get_cached_bnode(krcp); - if (!bnode) { - /* - * To keep this path working on raw non-preemptible - * sections, prevent the optional entry into the - * allocator as it uses sleeping locks. In fact, even - * if the caller of kfree_rcu() is preemptible, this - * path still is not, as krcp->lock is a raw spinlock. - * With additional page pre-allocation in the works, - * hitting this return is going to be much less likely. - */ - if (IS_ENABLED(CONFIG_PREEMPT_RT)) - return false; - - /* - * NOTE: For one argument of kvfree_rcu() we can - * drop the lock and get the page in sleepable - * context. That would allow to maintain an array - * for the CONFIG_PREEMPT_RT as well if no cached - * pages are available. - */ - bnode = (struct kvfree_rcu_bulk_data *) - __get_free_page(GFP_NOWAIT | __GFP_NOWARN); - } - /* Switch to emergency path. */ - if (unlikely(!bnode)) + if (!bnode) return false; /* Initialize the new block. */ @@ -3457,12 +3492,10 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) goto unlock_return; } - /* - * Under high memory pressure GFP_NOWAIT can fail, - * in that case the emergency path is maintained. - */ success = kvfree_call_rcu_add_ptr_to_bulk(krcp, ptr); if (!success) { + run_page_cache_worker(krcp); + if (head == NULL) // Inline if kvfree_rcu(one_arg) call. goto unlock_return; @@ -4482,24 +4515,14 @@ static void __init kfree_rcu_batch_init(void) for_each_possible_cpu(cpu) { struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); - struct kvfree_rcu_bulk_data *bnode; for (i = 0; i < KFREE_N_BATCHES; i++) { INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work); krcp->krw_arr[i].krcp = krcp; } - for (i = 0; i < rcu_min_cached_objs; i++) { - bnode = (struct kvfree_rcu_bulk_data *) - __get_free_page(GFP_NOWAIT | __GFP_NOWARN); - - if (bnode) - put_cached_bnode(krcp, bnode); - else - pr_err("Failed to preallocate for %d CPU!\n", cpu); - } - INIT_DELAYED_WORK(&krcp->monitor_work, kfree_rcu_monitor); + INIT_WORK(&krcp->page_cache_work, fill_page_cache_func); krcp->initialized = true; } if (register_shrinker(&kfree_rcu_shrinker)) -- cgit v1.2.3-59-g8ed1b From 50edb988534c621a56ca103c0c16ac59e7399f01 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 10 Sep 2020 11:54:42 -0700 Subject: srcu: Take early exit on memory-allocation failure It turns out that init_srcu_struct() can be invoked from usermode tasks, and that fatal signals received by these tasks can cause memory-allocation failures. These failures are not handled well by init_srcu_struct(), so much so that NULL pointer dereferences can result. This commit therefore causes init_srcu_struct() to take an early exit upon detection of memory-allocation failure. Link: https://lore.kernel.org/lkml/20200908144306.33355-1-aik@ozlabs.ru/ Reported-by: Alexey Kardashevskiy Tested-by: Alexey Kardashevskiy Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutree.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index c13348ee80a5..6f7880acfdd5 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -177,11 +177,13 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static) INIT_DELAYED_WORK(&ssp->work, process_srcu); if (!is_static) ssp->sda = alloc_percpu(struct srcu_data); + if (!ssp->sda) + return -ENOMEM; init_srcu_struct_nodes(ssp, is_static); ssp->srcu_gp_seq_needed_exp = 0; ssp->srcu_last_gp_end = ktime_get_mono_fast_ns(); smp_store_release(&ssp->srcu_gp_seq_needed, 0); /* Init done. */ - return ssp->sda ? 0 : -ENOMEM; + return 0; } #ifdef CONFIG_DEBUG_LOCK_ALLOC -- cgit v1.2.3-59-g8ed1b