From 8f4c53c804fbc30a305bf13376f5748a55ec4944 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 9 Mar 2021 09:55:57 +0100 Subject: [PATCH 150/323] tick/sched: Prevent false positive softirq pending warnings on RT Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz On RT a task which has soft interrupts disabled can block on a lock and schedule out to idle while soft interrupts are pending. This triggers the warning in the NOHZ idle code which complains about going idle with pending soft interrupts. But as the task is blocked soft interrupt processing is temporarily blocked as well which means that such a warning is a false positive. To prevent that check the per CPU state which indicates that a scheduled out task has soft interrupts disabled. Signed-off-by: Thomas Gleixner Tested-by: Sebastian Andrzej Siewior Reviewed-by: Frederic Weisbecker Signed-off-by: Sebastian Andrzej Siewior --- include/linux/bottom_half.h | 6 ++++++ kernel/softirq.c | 15 +++++++++++++++ kernel/time/tick-sched.c | 2 +- 3 files changed, 22 insertions(+), 1 deletion(-) diff --git a/include/linux/bottom_half.h b/include/linux/bottom_half.h index e4dd613a070e..eed86eb0a1de 100644 --- a/include/linux/bottom_half.h +++ b/include/linux/bottom_half.h @@ -32,4 +32,10 @@ static inline void local_bh_enable(void) __local_bh_enable_ip(_THIS_IP_, SOFTIRQ_DISABLE_OFFSET); } +#ifdef CONFIG_PREEMPT_RT +extern bool local_bh_blocked(void); +#else +static inline bool local_bh_blocked(void) { return false; } +#endif + #endif /* _LINUX_BH_H */ diff --git a/kernel/softirq.c b/kernel/softirq.c index ed13f6097de8..c9adc5c46248 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -139,6 +139,21 @@ static DEFINE_PER_CPU(struct softirq_ctrl, softirq_ctrl) = { .lock = INIT_LOCAL_LOCK(softirq_ctrl.lock), }; +/** + * local_bh_blocked() - Check for idle whether BH processing is blocked + * + * Returns false if the per CPU softirq::cnt is 0 otherwise true. + * + * This is invoked from the idle task to guard against false positive + * softirq pending warnings, which would happen when the task which holds + * softirq_ctrl::lock was the only running task on the CPU and blocks on + * some other lock. + */ +bool local_bh_blocked(void) +{ + return __this_cpu_read(softirq_ctrl.cnt) != 0; +} + void __local_bh_disable_ip(unsigned long ip, unsigned int cnt) { unsigned long flags; diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index fc79b04b5947..fb10be8e5e92 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -982,7 +982,7 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) if (unlikely(local_softirq_pending())) { static int ratelimit; - if (ratelimit < 10 && + 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()); -- 2.43.0