From c964c1f5ee96e1460606d44f80a47bdacd8fe568 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 8 Sep 2023 22:35:59 +0200 Subject: rcu: Assume rcu_report_dead() is always called locally rcu_report_dead() has to be called locally by the CPU that is going to exit the RCU state machine. Passing a cpu argument here is error-prone and leaves the possibility for a racy remote call. Use local access instead. Reviewed-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker --- kernel/cpu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/cpu.c') diff --git a/kernel/cpu.c b/kernel/cpu.c index 6de7c6bb74ee..076e75fed8bb 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -1388,7 +1388,7 @@ void cpuhp_report_idle_dead(void) struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state); BUG_ON(st->state != CPUHP_AP_OFFLINE); - rcu_report_dead(smp_processor_id()); + rcu_report_dead(); st->state = CPUHP_AP_IDLE_DEAD; /* * We cannot call complete after rcu_report_dead() so we delegate it -- cgit v1.2.3 From 448e9f34d91d1a4799fdb06a93c2c24b34b6fd9d Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 8 Sep 2023 22:36:01 +0200 Subject: rcu: Standardize explicit CPU-hotplug calls rcu_report_dead() and rcutree_migrate_callbacks() have their headers in rcupdate.h while those are pure rcutree calls, like the other CPU-hotplug functions. Also rcu_cpu_starting() and rcu_report_dead() have different naming conventions while they mirror each other's effects. Fix the headers and propose a naming that relates both functions and aligns with the prefix of other rcutree CPU-hotplug functions. Reviewed-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker --- .../Expedited-Grace-Periods/Expedited-Grace-Periods.rst | 2 +- Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg | 4 ++-- Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg | 4 ++-- Documentation/RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg | 4 ++-- Documentation/RCU/Design/Requirements/Requirements.rst | 4 ++-- arch/arm64/kernel/smp.c | 4 ++-- arch/powerpc/kernel/smp.c | 2 +- arch/s390/kernel/smp.c | 2 +- arch/x86/kernel/smpboot.c | 2 +- include/linux/interrupt.h | 2 +- include/linux/rcupdate.h | 2 -- include/linux/rcutiny.h | 2 +- include/linux/rcutree.h | 7 ++++++- kernel/cpu.c | 6 +++--- kernel/rcu/tree.c | 12 ++++++++---- 15 files changed, 33 insertions(+), 26 deletions(-) (limited to 'kernel/cpu.c') diff --git a/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst b/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst index 93d899d53258..414f8a2012d6 100644 --- a/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst +++ b/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst @@ -181,7 +181,7 @@ operations is carried out at several levels: of this wait (or series of waits, as the case may be) is to permit a concurrent CPU-hotplug operation to complete. #. In the case of RCU-sched, one of the last acts of an outgoing CPU is - to invoke ``rcu_report_dead()``, which reports a quiescent state for + to invoke ``rcutree_report_cpu_dead()``, which reports a quiescent state for that CPU. However, this is likely paranoia-induced redundancy. +-----------------------------------------------------------------------+ diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg index 7ddc094d7f28..d82a77d03d8c 100644 --- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg +++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg @@ -1135,7 +1135,7 @@ font-weight="bold" font-size="192" id="text202-7-5-3-27-6-5" - style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_report_dead() + style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcutree_report_cpu_dead() rcu_cpu_starting() + xml:space="preserve">rcutree_report_cpu_starting() rcu_report_dead() + style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcutree_report_cpu_dead() rcu_cpu_starting() + xml:space="preserve">rcutree_report_cpu_starting() rcu_report_dead() + style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcutree_report_cpu_dead() rcu_cpu_starting() + xml:space="preserve">rcutree_report_cpu_starting() setup_cpu) diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c index a4edb7ea66ea..214a1b67f80a 100644 --- a/arch/s390/kernel/smp.c +++ b/arch/s390/kernel/smp.c @@ -898,7 +898,7 @@ static void smp_start_secondary(void *cpuvoid) S390_lowcore.restart_flags = 0; restore_access_regs(S390_lowcore.access_regs_save_area); cpu_init(); - rcu_cpu_starting(cpu); + rcutree_report_cpu_starting(cpu); init_cpu_timer(); vtime_init(); vdso_getcpu_init(); diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 4e45ff44aa07..4ccb76f89af8 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -288,7 +288,7 @@ static void notrace start_secondary(void *unused) cpu_init(); fpu__init_cpu(); - rcu_cpu_starting(raw_smp_processor_id()); + rcutree_report_cpu_starting(raw_smp_processor_id()); x86_cpuinit.early_percpu_clock_init(); ap_starting(); diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h index a92bce40b04b..d05e1e9a553c 100644 --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -566,7 +566,7 @@ enum * * _ RCU: * 1) rcutree_migrate_callbacks() migrates the queue. - * 2) rcu_report_dead() reports the final quiescent states. + * 2) rcutree_report_cpu_dead() reports the final quiescent states. * * _ IRQ_POLL: irq_poll_cpu_dead() migrates the queue */ diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index aa351ddcbe8d..f7206b2623c9 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -122,8 +122,6 @@ static inline void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func) void rcu_init(void); extern int rcu_scheduler_active; void rcu_sched_clock_irq(int user); -void rcu_report_dead(void); -void rcutree_migrate_callbacks(int cpu); #ifdef CONFIG_TASKS_RCU_GENERIC void rcu_init_tasks_generic(void); diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 7b949292908a..d9ac7b136aea 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -171,6 +171,6 @@ static inline void rcu_all_qs(void) { barrier(); } #define rcutree_offline_cpu NULL #define rcutree_dead_cpu NULL #define rcutree_dying_cpu NULL -static inline void rcu_cpu_starting(unsigned int cpu) { } +static inline void rcutree_report_cpu_starting(unsigned int cpu) { } #endif /* __LINUX_RCUTINY_H */ diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 46875c4e9f56..254244202ea9 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -110,7 +110,7 @@ void rcu_all_qs(void); /* RCUtree hotplug events */ int rcutree_prepare_cpu(unsigned int cpu); int rcutree_online_cpu(unsigned int cpu); -void rcu_cpu_starting(unsigned int cpu); +void rcutree_report_cpu_starting(unsigned int cpu); #ifdef CONFIG_HOTPLUG_CPU int rcutree_dead_cpu(unsigned int cpu); @@ -122,4 +122,9 @@ int rcutree_offline_cpu(unsigned int cpu); #define rcutree_offline_cpu NULL #endif +void rcutree_migrate_callbacks(int cpu); + +/* Called from hotplug and also arm64 early secondary boot failure */ +void rcutree_report_cpu_dead(void); + #endif /* __LINUX_RCUTREE_H */ diff --git a/kernel/cpu.c b/kernel/cpu.c index 076e75fed8bb..2491766e1fd5 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -1388,10 +1388,10 @@ void cpuhp_report_idle_dead(void) struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state); BUG_ON(st->state != CPUHP_AP_OFFLINE); - rcu_report_dead(); + rcutree_report_cpu_dead(); st->state = CPUHP_AP_IDLE_DEAD; /* - * We cannot call complete after rcu_report_dead() so we delegate it + * We cannot call complete after rcutree_report_cpu_dead() so we delegate it * to an online cpu. */ smp_call_function_single(cpumask_first(cpu_online_mask), @@ -1617,7 +1617,7 @@ void notify_cpu_starting(unsigned int cpu) struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu); enum cpuhp_state target = min((int)st->target, CPUHP_AP_ONLINE); - rcu_cpu_starting(cpu); /* Enables RCU usage on this CPU. */ + rcutree_report_cpu_starting(cpu); /* Enables RCU usage on this CPU. */ cpumask_set_cpu(cpu, &cpus_booted_once_mask); /* diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index f9c6b2680cbb..36d8818eaec1 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -4216,7 +4216,7 @@ bool rcu_lockdep_current_cpu_online(void) rdp = this_cpu_ptr(&rcu_data); /* * Strictly, we care here about the case where the current CPU is - * in rcu_cpu_starting() and thus has an excuse for rdp->grpmask + * in rcutree_report_cpu_starting() and thus has an excuse for rdp->grpmask * not being up to date. So arch_spin_is_locked() might have a * false positive if it's held by some *other* CPU, but that's * OK because that just means a false *negative* on the warning. @@ -4445,8 +4445,10 @@ int rcutree_online_cpu(unsigned int cpu) * from the incoming CPU rather than from the cpuhp_step mechanism. * This is because this function must be invoked at a precise location. * This incoming CPU must not have enabled interrupts yet. + * + * This mirrors the effects of rcutree_report_cpu_dead(). */ -void rcu_cpu_starting(unsigned int cpu) +void rcutree_report_cpu_starting(unsigned int cpu) { unsigned long mask; struct rcu_data *rdp; @@ -4500,8 +4502,10 @@ void rcu_cpu_starting(unsigned int cpu) * Note that this function is special in that it is invoked directly * from the outgoing CPU rather than from the cpuhp_step mechanism. * This is because this function must be invoked at a precise location. + * + * This mirrors the effect of rcutree_report_cpu_starting(). */ -void rcu_report_dead(void) +void rcutree_report_cpu_dead(void) { unsigned long flags; unsigned long mask; @@ -5072,7 +5076,7 @@ void __init rcu_init(void) pm_notifier(rcu_pm_notify, 0); WARN_ON(num_online_cpus() > 1); // Only one CPU this early in boot. rcutree_prepare_cpu(cpu); - rcu_cpu_starting(cpu); + rcutree_report_cpu_starting(cpu); rcutree_online_cpu(cpu); /* Create workqueue for Tree SRCU and for expedited GPs. */ -- cgit v1.2.3 From a28ab03b499601c14b8f502d875c2bee23209659 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 8 Sep 2023 22:36:03 +0200 Subject: rcu: Comment why callbacks migration can't wait for CPUHP_RCUTREE_PREP The callbacks migration is performed through an explicit call from the hotplug control CPU right after the death of the target CPU and before proceeding with the CPUHP_ teardown functions. This is unusual but necessary and yet uncommented. Summarize the reason as explained in the changelog of: a58163d8ca2c (rcu: Migrate callbacks earlier in the CPU-offline timeline) Reviewed-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker --- kernel/cpu.c | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'kernel/cpu.c') diff --git a/kernel/cpu.c b/kernel/cpu.c index 2491766e1fd5..3b9d5c7eb4a2 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -1372,7 +1372,14 @@ static int takedown_cpu(unsigned int cpu) cpuhp_bp_sync_dead(cpu); tick_cleanup_dead_cpu(cpu); + + /* + * Callbacks must be re-integrated right away to the RCU state machine. + * Otherwise an RCU callback could block a further teardown function + * waiting for its completion. + */ rcutree_migrate_callbacks(cpu); + return 0; } -- cgit v1.2.3