linux-kernel - Re: [PATCH] sched: Dump stacktrace when some task failed to stop

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Message-ID: <xhsmha6bd1o6a.mognet@vschneid.remote.csb>
Date:   Thu, 19 May 2022 17:29:17 +0100
From:   Valentin Schneider <vschneid@...hat.com>
To:     Schspa Shi <schspa@...il.com>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com
Cc:     linux-kernel@...r.kernel.org, Schspa Shi <schspa@...il.com>
Subject: Re: [PATCH] sched: Dump stacktrace when some task failed to stop

On 20/05/22 00:11, Schspa Shi wrote:
> Some processes may not be stopped, such as workqueue workers.
>
> Add this dump_stack to easily figure out which process caused the problems.
>
> Before this change:
>
> <4>[  517.545889] ------------[ cut here ]------------
> <4>[  517.545901] Dying CPU not properly vacated!
> <4>[  517.546366] ---[ end trace 0000000000000002 ]---
> <4>[  518.546831] CPU6 enqueued tasks (2 total):
> <4>[  518.546855] 	pid: 49, name: migration/6
> <4>[  518.547010] 	pid: 6231, name: kworker/6:0
>
> Signed-off-by: Schspa Shi <schspa@...il.com>
> ---
>  kernel/sched/core.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 53596842f0d8..de6b5320e4d7 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -9416,7 +9416,14 @@ static void dump_rq_tasks(struct rq *rq, const char *loglvl)
>  			continue;
>  
>  		printk("%s\tpid: %d, name: %s\n", loglvl, p->pid, p->comm);
> +		if (p != current)
> +			sched_show_task(p);
>  	}
> +	/*
> +	 * We need the stack of each cpu to analyze who is blocking the
> +	 * current cpu scheduling
> +	 */
> +	trigger_all_cpu_backtrace();
>  }
>

Given you get a WARN() when this happens, can't you get the same thing with

  panic_on_warn=1
  panic_print=PANIC_PRINT_ALL_CPU_BT

?

>  int sched_cpu_dying(unsigned int cpu)
> -- 
> 2.24.3 (Apple Git-128)