Commit 47c218dc authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

tick/sched: Prevent false positive softirq pending warnings on RT 



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: default avatarThomas Gleixner <tglx@linutronix.de>
Tested-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Reviewed-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210309085727.527563866@linutronix.de
parent 8b1c04ac

include/linux/bottom_half.h

+6 −0
Original line number Diff line number Diff line
@@ -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 */

kernel/softirq.c

+15 −0
Original line number Diff line number Diff line
@@ -141,6 +141,21 @@ 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;

kernel/time/tick-sched.c

+1 −1
Original line number Diff line number Diff line
@@ -973,7 +973,7 @@ 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());