linux-kernel - Re: [PATCH RFC exit] Sleep at TASK_IDLE when waiting for application core dump

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Message-ID: <20240725170951.GB6602@redhat.com>
Date: Thu, 25 Jul 2024 19:09:52 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: linux-kernel@...r.kernel.org, axboe@...nel.dk, brauner@...nel.org,
	akpm@...ux-foundation.org, willy@...radead.org, clm@...com,
	riel@...riel.com, ffledgling@...a.com
Subject: Re: [PATCH RFC exit] Sleep at TASK_IDLE when waiting for application
 core dump

On 07/25, Paul E. McKenney wrote:
>
> How does the updated patch shown below look to you?

Thanks, looks good to me ;)

Oleg.

> ------------------------------------------------------------------------
> 
> commit a6c7779283d67a409b81616a5b485ac21637d7e7
> Author: Paul E. McKenney <paulmck@...nel.org>
> Date:   Wed Jul 24 16:51:52 2024 -0700
> 
>     exit: Sleep at TASK_IDLE when waiting for application core dump
>     
>     Currently, the coredump_task_exit() function sets the task state
>     to TASK_UNINTERRUPTIBLE|TASK_FREEZABLE, which usually works well.
>     But a combination of large memory and slow (and/or highly contended)
>     mass storage can cause application core dumps to take more than
>     two minutes, which can cause check_hung_task(), which is invoked by
>     check_hung_uninterruptible_tasks(), to produce task-blocked splats.
>     There does not seem to be any reasonable benefit to getting these splats.
>     
>     Furthermore, as Oleg Nesterov points out, TASK_UNINTERRUPTIBLE could
>     be misleading because the task sleeping in coredump_task_exit() really
>     is killable, albeit indirectly.  See the check of signal->core_state
>     in prepare_signal() and the check of fatal_signal_pending()
>     in dump_interrupted(), which bypass the normal unkillability of
>     TASK_UNINTERRUPTIBLE, resulting in coredump_finish() invoking
>     wake_up_process() on any threads sleeping in coredump_task_exit().
>     
>     Therefore, change that TASK_UNINTERRUPTIBLE to TASK_IDLE.
>     
>     Reported-by: Anhad Jai Singh <ffledgling@...a.com>
>     Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
>     Acked-by: Oleg Nesterov <oleg@...hat.com>
>     Cc: Jens Axboe <axboe@...nel.dk>
>     Cc: Christian Brauner <brauner@...nel.org>
>     Cc: Andrew Morton <akpm@...ux-foundation.org>
>     Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>
>     Cc: Chris Mason <clm@...com>
>     Cc: Rik van Riel <riel@...riel.com>
> 
> diff --git a/kernel/exit.c b/kernel/exit.c
> index f95a2c1338a8..b0d18f7b6d15 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -429,7 +429,7 @@ static void coredump_task_exit(struct task_struct *tsk)
>  			complete(&core_state->startup);
>  
>  		for (;;) {
> -			set_current_state(TASK_UNINTERRUPTIBLE|TASK_FREEZABLE);
> +			set_current_state(TASK_IDLE|TASK_FREEZABLE);
>  			if (!self.task) /* see coredump_finish() */
>  				break;
>  			schedule();
>