From: Frederic Weisbecker <frederic@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Paul McKenney <paulmck@kernel.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: Re: [patch V2 5/9] tick/sched: Prevent false positive softirq pending warnings on RT
Date: Tue, 8 Dec 2020 13:23:00 +0100 [thread overview]
Message-ID: <20201208122300.GA16597@lothringen> (raw)
In-Reply-To: <20201204170805.232293729@linutronix.de>
On Fri, Dec 04, 2020 at 06:01:56PM +0100, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
>
> 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 <tglx@linutronix.de>
> ---
> include/linux/bottom_half.h | 6 ++++++
> kernel/softirq.c | 15 +++++++++++++++
> kernel/time/tick-sched.c | 2 +-
> 3 files changed, 22 insertions(+), 1 deletion(-)
>
> --- 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 */
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -138,6 +138,21 @@ static DEFINE_PER_CPU(struct softirq_ctr
> .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;
__this_cpu_read()
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
next prev parent reply other threads:[~2020-12-08 12:24 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-04 17:01 [patch V2 0/9] softirq: Make it RT aware Thomas Gleixner
2020-12-04 17:01 ` [patch V2 1/9] softirq: Add RT specific softirq accounting Thomas Gleixner
2020-12-07 13:06 ` Frederic Weisbecker
2020-12-04 17:01 ` [patch V2 2/9] irqtime: Make accounting correct on RT Thomas Gleixner
2020-12-07 0:23 ` Frederic Weisbecker
2020-12-07 0:57 ` Thomas Gleixner
2020-12-07 1:14 ` Frederic Weisbecker
2020-12-07 13:27 ` Frederic Weisbecker
2020-12-07 14:44 ` Thomas Gleixner
2020-12-04 17:01 ` [patch V2 3/9] softirq: Move various protections into inline helpers Thomas Gleixner
2020-12-07 13:37 ` Frederic Weisbecker
2020-12-04 17:01 ` [patch V2 4/9] softirq: Make softirq control and processing RT aware Thomas Gleixner
2020-12-07 14:16 ` Frederic Weisbecker
2020-12-07 15:08 ` Thomas Gleixner
2020-12-08 0:08 ` Frederic Weisbecker
2020-12-09 10:11 ` Peter Zijlstra
2020-12-09 12:36 ` Thomas Gleixner
2020-12-09 12:42 ` Peter Zijlstra
2020-12-09 13:30 ` Thomas Gleixner
2020-12-09 10:34 ` Peter Zijlstra
2020-12-04 17:01 ` [patch V2 5/9] tick/sched: Prevent false positive softirq pending warnings on RT Thomas Gleixner
2020-12-08 12:23 ` Frederic Weisbecker [this message]
2020-12-04 17:01 ` [patch V2 6/9] rcu: Prevent false positive softirq warning " Thomas Gleixner
2020-12-04 17:59 ` Paul E. McKenney
2020-12-04 17:01 ` [patch V2 7/9] softirq: Replace barrier() with cpu_relax() in tasklet_unlock_wait() Thomas Gleixner
2020-12-07 11:39 ` Peter Zijlstra
2020-12-07 15:21 ` Thomas Gleixner
2020-12-04 17:01 ` [patch V2 8/9] tasklets: Use static inlines for stub implementations Thomas Gleixner
2020-12-04 17:02 ` [patch V2 9/9] tasklets: Prevent kill/unlock_wait deadlock on RT Thomas Gleixner
2020-12-07 11:47 ` Peter Zijlstra
2020-12-07 14:00 ` Sebastian Andrzej Siewior
2020-12-07 14:27 ` Peter Zijlstra
2020-12-07 17:55 ` Thomas Gleixner
2020-12-07 15:22 ` Thomas Gleixner
2020-12-07 15:39 ` Sebastian Andrzej Siewior
2020-12-07 17:49 ` Thomas Gleixner
2020-12-07 17:50 ` Thomas Gleixner
2020-12-06 10:05 ` [patch V2 0/9] softirq: Make it RT aware Sebastian Andrzej Siewior
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