linux-kernel - Re: [patch 1/2] sched/debug: Change need_resched warnings to pr

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Message-ID: <CABk29NtGj6keZf=O2VUykTns-r16di7TUhLF1NcY5OBWx2YGTg@mail.gmail.com>
Date: Mon, 6 Jan 2025 13:59:35 -0800
From: Josh Don <joshdon@...gle.com>
To: David Rientjes <rientjes@...gle.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
	Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, 
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Valentin Schneider <vschneid@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/2] sched/debug: Change need_resched warnings to pr_err

On Mon, Jan 6, 2025 at 12:39 PM David Rientjes <rientjes@...gle.com> wrote:
>
> need_resched warnings, if enabled, are treated as WARNINGs.  If
> kernel.panic_on_warn is enabled, then this causes a kernel panic.
>
> It's highly unlikely that a panic is desired for these warnings, only a
> stack trace is normally required to debug and resolve.
>
> Thus, switch need_resched warnings to simply be a printk with an
> associated stack trace so they are no longer in scope for panic_on_warn.
>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>  kernel/sched/debug.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -1295,8 +1295,10 @@ void resched_latency_warn(int cpu, u64 latency)
>  {
>         static DEFINE_RATELIMIT_STATE(latency_check_ratelimit, 60 * 60 * HZ, 1);
>
> -       WARN(__ratelimit(&latency_check_ratelimit),
> -            "sched: CPU %d need_resched set for > %llu ns (%d ticks) "
> -            "without schedule\n",
> -            cpu, latency, cpu_rq(cpu)->ticks_without_resched);
> +       if (likely(!__ratelimit(&latency_check_ratelimit)))
> +               return;
> +
> +       pr_err("sched: CPU %d need_resched set for > %llu ns (%d ticks) without schedule\n",
> +              cpu, latency, cpu_rq(cpu)->ticks_without_resched);
> +       dump_stack();
>  }
>

Thanks David, looks reasonable to me.

Acked-by: Josh Don <joshdon@...gle.com>