From 2984539959dbaf4e65e19bf90c2419304a81a985 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Tue, 8 Feb 2022 17:16:33 +0100 Subject: tick/rcu: Remove obsolete rcu_needs_cpu() parameters With the removal of CONFIG_RCU_FAST_NO_HZ, the parameters in rcu_needs_cpu() are not necessary anymore. Simply remove them. Signed-off-by: Frederic Weisbecker Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Paul E. McKenney Cc: Paul Menzel --- include/linux/rcutiny.h | 3 +-- include/linux/rcutree.h | 2 +- 2 files changed, 2 insertions(+), 3 deletions(-) (limited to 'include/linux') diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 858f4d429946..5fed476f977f 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -64,9 +64,8 @@ static inline void rcu_softirq_qs(void) rcu_tasks_qs(current, (preempt)); \ } while (0) -static inline int rcu_needs_cpu(u64 basemono, u64 *nextevt) +static inline int rcu_needs_cpu(void) { - *nextevt = KTIME_MAX; return 0; } diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 53209d669400..6cc91291d078 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -19,7 +19,7 @@ void rcu_softirq_qs(void); void rcu_note_context_switch(bool preempt); -int rcu_needs_cpu(u64 basem, u64 *nextevt); +int rcu_needs_cpu(void); void rcu_cpu_stall_reset(void); /* -- cgit v1.2.3 From 0345691b24c076655ce8f0f4bfd24cba3467ccbd Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Tue, 8 Feb 2022 17:16:34 +0100 Subject: tick/rcu: Stop allowing RCU_SOFTIRQ in idle RCU_SOFTIRQ used to be special in that it could be raised on purpose within the idle path to prevent from stopping the tick. Some code still prevents from unnecessary warnings related to this specific behaviour while entering in dynticks-idle mode. However the nohz layout has changed quite a bit in ten years, and the removal of CONFIG_RCU_FAST_NO_HZ has been the final straw to this safe-conduct. Now the RCU_SOFTIRQ vector is expected to be raised from sane places. A remaining corner case is admitted though when the vector is invoked in fragile hotplug path. Signed-off-by: Frederic Weisbecker Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Paul E. McKenney Cc: Paul Menzel --- include/linux/interrupt.h | 8 +++++++- kernel/time/tick-sched.c | 50 +++++++++++++++++++++++++++++++++++++---------- 2 files changed, 47 insertions(+), 11 deletions(-) (limited to 'include/linux') diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h index 9367f1cb2e3c..9613326d2f8a 100644 --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -579,7 +579,13 @@ enum NR_SOFTIRQS }; -#define SOFTIRQ_STOP_IDLE_MASK (~(1 << RCU_SOFTIRQ)) +/* + * Ignoring the RCU vector after ksoftirqd is parked is fine + * because: + * 1) rcutree_migrate_callbacks() takes care of the queue. + * 2) rcu_report_dead() reports the final quiescent states. + */ +#define SOFTIRQ_HOTPLUG_SAFE_MASK (BIT(RCU_SOFTIRQ)) /* map softirq index to softirq name. update 'softirq_to_name' in * kernel/softirq.c when adding a new softirq. diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 566ad5bd83e9..2d76c91b85de 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -999,6 +999,45 @@ static void tick_nohz_full_update_tick(struct tick_sched *ts) __tick_nohz_full_update_tick(ts, ktime_get()); } +/* + * A pending softirq outside an IRQ (or softirq disabled section) context + * should be waiting for ksoftirqd to handle it. Therefore we shouldn't + * reach here due to the need_resched() early check in can_stop_idle_tick(). + * + * However if we are between CPUHP_AP_SMPBOOT_THREADS and CPU_TEARDOWN_CPU on the + * cpu_down() process, softirqs can still be raised while ksoftirqd is parked, + * triggering the below since wakep_softirqd() is ignored. + * + */ +static bool report_idle_softirq(void) +{ + static int ratelimit; + unsigned int pending = local_softirq_pending(); + + if (likely(!pending)) + return false; + + /* Some softirqs claim to be safe against hotplug and ksoftirqd parking */ + if (!cpu_active(smp_processor_id())) { + pending &= ~SOFTIRQ_HOTPLUG_SAFE_MASK; + if (!pending) + return false; + } + + if (ratelimit < 10) + return false; + + /* On RT, softirqs handling may be waiting on some lock */ + if (!local_bh_blocked()) + return false; + + pr_warn("NOHZ tick-stop error: local softirq work is pending, handler #%02x!!!\n", + pending); + ratelimit++; + + return true; +} + static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) { /* @@ -1025,17 +1064,8 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) if (need_resched()) return false; - if (unlikely(local_softirq_pending())) { - static int ratelimit; - - if (ratelimit < 10 && !local_bh_blocked() && - (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) { - pr_warn("NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #%02x!!!\n", - (unsigned int) local_softirq_pending()); - ratelimit++; - } + if (unlikely(report_idle_softirq())) return false; - } if (tick_nohz_full_enabled()) { /* -- cgit v1.2.3 From f96272a90d9eaea9933aaab704ddbd258feb3841 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Tue, 8 Feb 2022 17:16:35 +0100 Subject: lib/irq_poll: Declare IRQ_POLL softirq vector as ksoftirqd-parking safe The following warning may appear while setting a CPU down: NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #20!!! The IRQ_POLL_SOFTIRQ vector can be raised during the hotplug cpu_down() path after ksoftirqd is parked and before the CPU actually dies. However this is handled afterward at the CPUHP_IRQ_POLL_DEAD stage where the queue gets migrated. Hence this warning can be considered spurious and the vector can join the "hotplug-safe" list. Reported-and-tested-by: Paul Menzel Signed-off-by: Frederic Weisbecker Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Paul E. McKenney Cc: Paul Menzel --- include/linux/interrupt.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) (limited to 'include/linux') diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h index 9613326d2f8a..f40754caaefa 100644 --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -580,12 +580,15 @@ enum }; /* - * Ignoring the RCU vector after ksoftirqd is parked is fine - * because: - * 1) rcutree_migrate_callbacks() takes care of the queue. + * The following vectors can be safely ignored after ksoftirqd is parked: + * + * _ RCU: + * 1) rcutree_migrate_callbacks() migrates the queue. * 2) rcu_report_dead() reports the final quiescent states. + * + * _ IRQ_POLL: irq_poll_cpu_dead() migrates the queue */ -#define SOFTIRQ_HOTPLUG_SAFE_MASK (BIT(RCU_SOFTIRQ)) +#define SOFTIRQ_HOTPLUG_SAFE_MASK (BIT(RCU_SOFTIRQ) | BIT(IRQ_POLL_SOFTIRQ)) /* map softirq index to softirq name. update 'softirq_to_name' in * kernel/softirq.c when adding a new softirq. -- cgit v1.2.3