diff options
Diffstat (limited to 'kernel/rcu/tree_nocb.h')
| -rw-r--r-- | kernel/rcu/tree_nocb.h | 160 |
1 files changed, 106 insertions, 54 deletions
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index 368ef7b9af4f..eeafb546a7a0 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -60,16 +60,22 @@ static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp) * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. * If the list is invalid, a warning is emitted and all CPUs are offloaded. */ + +static bool rcu_nocb_is_setup; + static int __init rcu_nocb_setup(char *str) { alloc_bootmem_cpumask_var(&rcu_nocb_mask); - if (cpulist_parse(str, rcu_nocb_mask)) { - pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n"); - cpumask_setall(rcu_nocb_mask); + if (*str == '=') { + if (cpulist_parse(++str, rcu_nocb_mask)) { + pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n"); + cpumask_setall(rcu_nocb_mask); + } } + rcu_nocb_is_setup = true; return 1; } -__setup("rcu_nocbs=", rcu_nocb_setup); +__setup("rcu_nocbs", rcu_nocb_setup); static int __init parse_rcu_nocb_poll(char *arg) { @@ -625,7 +631,21 @@ static void nocb_gp_wait(struct rcu_data *my_rdp) * and the global grace-period kthread are awakened if needed. */ WARN_ON_ONCE(my_rdp->nocb_gp_rdp != my_rdp); - for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_cb_rdp) { + /* + * An rcu_data structure is removed from the list after its + * CPU is de-offloaded and added to the list before that CPU is + * (re-)offloaded. If the following loop happens to be referencing + * that rcu_data structure during the time that the corresponding + * CPU is de-offloaded and then immediately re-offloaded, this + * loop's rdp pointer will be carried to the end of the list by + * the resulting pair of list operations. This can cause the loop + * to skip over some of the rcu_data structures that were supposed + * to have been scanned. Fortunately a new iteration through the + * entire loop is forced after a given CPU's rcu_data structure + * is added to the list, so the skipped-over rcu_data structures + * won't be ignored for long. + */ + list_for_each_entry_rcu(rdp, &my_rdp->nocb_head_rdp, nocb_entry_rdp, 1) { bool needwake_state = false; if (!nocb_gp_enabled_cb(rdp)) @@ -789,6 +809,18 @@ static void nocb_cb_wait(struct rcu_data *rdp) bool can_sleep = true; struct rcu_node *rnp = rdp->mynode; + do { + swait_event_interruptible_exclusive(rdp->nocb_cb_wq, + nocb_cb_wait_cond(rdp)); + + // VVV Ensure CB invocation follows _sleep test. + if (smp_load_acquire(&rdp->nocb_cb_sleep)) { // ^^^ + WARN_ON(signal_pending(current)); + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty")); + } + } while (!nocb_cb_can_run(rdp)); + + local_irq_save(flags); rcu_momentary_dyntick_idle(); local_irq_restore(flags); @@ -841,17 +873,6 @@ static void nocb_cb_wait(struct rcu_data *rdp) if (needwake_state) swake_up_one(&rdp->nocb_state_wq); - - do { - swait_event_interruptible_exclusive(rdp->nocb_cb_wq, - nocb_cb_wait_cond(rdp)); - - // VVV Ensure CB invocation follows _sleep test. - if (smp_load_acquire(&rdp->nocb_cb_sleep)) { // ^^^ - WARN_ON(signal_pending(current)); - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty")); - } - } while (!nocb_cb_can_run(rdp)); } /* @@ -990,22 +1011,33 @@ static long rcu_nocb_rdp_deoffload(void *arg) * will refuse to put anything into the bypass. */ WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies)); + /* + * Start with invoking rcu_core() early. This way if the current thread + * happens to preempt an ongoing call to rcu_core() in the middle, + * leaving some work dismissed because rcu_core() still thinks the rdp is + * completely offloaded, we are guaranteed a nearby future instance of + * rcu_core() to catch up. + */ + rcu_segcblist_set_flags(cblist, SEGCBLIST_RCU_CORE); + invoke_rcu_core(); ret = rdp_offload_toggle(rdp, false, flags); swait_event_exclusive(rdp->nocb_state_wq, !rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP)); + /* Stop nocb_gp_wait() from iterating over this structure. */ + list_del_rcu(&rdp->nocb_entry_rdp); /* * Lock one last time to acquire latest callback updates from kthreads * so we can later handle callbacks locally without locking. */ rcu_nocb_lock_irqsave(rdp, flags); /* - * Theoretically we could set SEGCBLIST_SOFTIRQ_ONLY after the nocb + * Theoretically we could clear SEGCBLIST_LOCKING after the nocb * lock is released but how about being paranoid for once? */ - rcu_segcblist_set_flags(cblist, SEGCBLIST_SOFTIRQ_ONLY); + rcu_segcblist_clear_flags(cblist, SEGCBLIST_LOCKING); /* - * With SEGCBLIST_SOFTIRQ_ONLY, we can't use + * Without SEGCBLIST_LOCKING, we can't use * rcu_nocb_unlock_irqrestore() anymore. */ raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); @@ -1057,15 +1089,26 @@ static long rcu_nocb_rdp_offload(void *arg) return -EINVAL; pr_info("Offloading %d\n", rdp->cpu); + + /* + * Cause future nocb_gp_wait() invocations to iterate over + * structure, resetting ->nocb_gp_sleep and waking up the related + * "rcuog". Since nocb_gp_wait() in turn locks ->nocb_gp_lock + * before setting ->nocb_gp_sleep again, we are guaranteed to + * iterate this newly added structure before "rcuog" goes to + * sleep again. + */ + list_add_tail_rcu(&rdp->nocb_entry_rdp, &rdp->nocb_gp_rdp->nocb_head_rdp); + /* - * Can't use rcu_nocb_lock_irqsave() while we are in - * SEGCBLIST_SOFTIRQ_ONLY mode. + * Can't use rcu_nocb_lock_irqsave() before SEGCBLIST_LOCKING + * is set. */ raw_spin_lock_irqsave(&rdp->nocb_lock, flags); /* * We didn't take the nocb lock while working on the - * rdp->cblist in SEGCBLIST_SOFTIRQ_ONLY mode. + * rdp->cblist with SEGCBLIST_LOCKING cleared (pure softirq/rcuc mode). * Every modifications that have been done previously on * rdp->cblist must be visible remotely by the nocb kthreads * upon wake up after reading the cblist flags. @@ -1084,6 +1127,14 @@ static long rcu_nocb_rdp_offload(void *arg) rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB) && rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP)); + /* + * All kthreads are ready to work, we can finally relieve rcu_core() and + * enable nocb bypass. + */ + rcu_nocb_lock_irqsave(rdp, flags); + rcu_segcblist_clear_flags(cblist, SEGCBLIST_RCU_CORE); + rcu_nocb_unlock_irqrestore(rdp, flags); + return ret; } @@ -1122,13 +1173,17 @@ void __init rcu_init_nohz(void) need_rcu_nocb_mask = true; #endif /* #if defined(CONFIG_NO_HZ_FULL) */ - if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) { - if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) { - pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n"); - return; + if (need_rcu_nocb_mask) { + if (!cpumask_available(rcu_nocb_mask)) { + if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) { + pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n"); + return; + } } + rcu_nocb_is_setup = true; } - if (!cpumask_available(rcu_nocb_mask)) + + if (!rcu_nocb_is_setup) return; #if defined(CONFIG_NO_HZ_FULL) @@ -1154,8 +1209,8 @@ void __init rcu_init_nohz(void) if (rcu_segcblist_empty(&rdp->cblist)) rcu_segcblist_init(&rdp->cblist); rcu_segcblist_offload(&rdp->cblist, true); - rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_KTHREAD_CB); - rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_KTHREAD_GP); + rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP); + rcu_segcblist_clear_flags(&rdp->cblist, SEGCBLIST_RCU_CORE); } rcu_organize_nocb_kthreads(); } @@ -1178,17 +1233,17 @@ static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) * rcuo CB kthread, spawn it. Additionally, if the rcuo GP kthread * for this CPU's group has not yet been created, spawn it as well. */ -static void rcu_spawn_one_nocb_kthread(int cpu) +static void rcu_spawn_cpu_nocb_kthread(int cpu) { struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); struct rcu_data *rdp_gp; struct task_struct *t; - /* - * If this isn't a no-CBs CPU or if it already has an rcuo kthread, - * then nothing to do. - */ - if (!rcu_is_nocb_cpu(cpu) || rdp->nocb_cb_kthread) + if (!rcu_scheduler_fully_active || !rcu_nocb_is_setup) + return; + + /* If there already is an rcuo kthread, then nothing to do. */ + if (rdp->nocb_cb_kthread) return; /* If we didn't spawn the GP kthread first, reorganize! */ @@ -1211,16 +1266,6 @@ static void rcu_spawn_one_nocb_kthread(int cpu) } /* - * If the specified CPU is a no-CBs CPU that does not already have its - * rcuo kthread, spawn it. - */ -static void rcu_spawn_cpu_nocb_kthread(int cpu) -{ - if (rcu_scheduler_fully_active) - rcu_spawn_one_nocb_kthread(cpu); -} - -/* * Once the scheduler is running, spawn rcuo kthreads for all online * no-CBs CPUs. This assumes that the early_initcall()s happen before * non-boot CPUs come online -- if this changes, we will need to add @@ -1230,8 +1275,10 @@ static void __init rcu_spawn_nocb_kthreads(void) { int cpu; - for_each_online_cpu(cpu) - rcu_spawn_cpu_nocb_kthread(cpu); + if (rcu_nocb_is_setup) { + for_each_online_cpu(cpu) + rcu_spawn_cpu_nocb_kthread(cpu); + } } /* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */ @@ -1251,7 +1298,6 @@ static void __init rcu_organize_nocb_kthreads(void) int nl = 0; /* Next GP kthread. */ struct rcu_data *rdp; struct rcu_data *rdp_gp = NULL; /* Suppress misguided gcc warn. */ - struct rcu_data *rdp_prev = NULL; if (!cpumask_available(rcu_nocb_mask)) return; @@ -1265,14 +1311,14 @@ static void __init rcu_organize_nocb_kthreads(void) * Should the corresponding CPU come online in the future, then * we will spawn the needed set of rcu_nocb_kthread() kthreads. */ - for_each_cpu(cpu, rcu_nocb_mask) { + for_each_possible_cpu(cpu) { rdp = per_cpu_ptr(&rcu_data, cpu); if (rdp->cpu >= nl) { /* New GP kthread, set up for CBs & next GP. */ gotnocbs = true; nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls; - rdp->nocb_gp_rdp = rdp; rdp_gp = rdp; + INIT_LIST_HEAD(&rdp->nocb_head_rdp); if (dump_tree) { if (!firsttime) pr_cont("%s\n", gotnocbscbs @@ -1285,12 +1331,12 @@ static void __init rcu_organize_nocb_kthreads(void) } else { /* Another CB kthread, link to previous GP kthread. */ gotnocbscbs = true; - rdp->nocb_gp_rdp = rdp_gp; - rdp_prev->nocb_next_cb_rdp = rdp; if (dump_tree) pr_cont(" %d", cpu); } - rdp_prev = rdp; + rdp->nocb_gp_rdp = rdp_gp; + if (cpumask_test_cpu(cpu, rcu_nocb_mask)) + list_add_tail(&rdp->nocb_entry_rdp, &rdp_gp->nocb_head_rdp); } if (gotnocbs && dump_tree) pr_cont("%s\n", gotnocbscbs ? "" : " (self only)"); @@ -1352,6 +1398,7 @@ static void show_rcu_nocb_state(struct rcu_data *rdp) { char bufw[20]; char bufr[20]; + struct rcu_data *nocb_next_rdp; struct rcu_segcblist *rsclp = &rdp->cblist; bool waslocked; bool wassleep; @@ -1359,11 +1406,16 @@ static void show_rcu_nocb_state(struct rcu_data *rdp) if (rdp->nocb_gp_rdp == rdp) show_rcu_nocb_gp_state(rdp); + nocb_next_rdp = list_next_or_null_rcu(&rdp->nocb_gp_rdp->nocb_head_rdp, + &rdp->nocb_entry_rdp, + typeof(*rdp), + nocb_entry_rdp); + sprintf(bufw, "%ld", rsclp->gp_seq[RCU_WAIT_TAIL]); sprintf(bufr, "%ld", rsclp->gp_seq[RCU_NEXT_READY_TAIL]); pr_info(" CB %d^%d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%s%c%s%c%c q%ld %c CPU %d%s\n", rdp->cpu, rdp->nocb_gp_rdp->cpu, - rdp->nocb_next_cb_rdp ? rdp->nocb_next_cb_rdp->cpu : -1, + nocb_next_rdp ? nocb_next_rdp->cpu : -1, "kK"[!!rdp->nocb_cb_kthread], "bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)], "cC"[!!atomic_read(&rdp->nocb_lock_contended)], |