linux-kernel - Re: [PATCH 1/2] completion: move blk_wait

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Date: Wed, 17 Apr 2024 19:55:38 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Mikulas Patocka <mpatocka@...hat.com>
Cc: Mike Snitzer <msnitzer@...hat.com>, Jens Axboe <axboe@...nel.dk>,
	Damien Le Moal <dlemoal@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>,
	Guangwu Zhang <guazhang@...hat.com>, dm-devel@...ts.linux.dev,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] completion: move blk_wait_io to
 kernel/sched/completion.c

On Wed, Apr 17, 2024 at 07:49:17PM +0200, Mikulas Patocka wrote:
> Index: linux-2.6/kernel/sched/completion.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched/completion.c	2024-04-17 19:41:14.000000000 +0200
> +++ linux-2.6/kernel/sched/completion.c	2024-04-17 19:41:14.000000000 +0200
> @@ -290,6 +290,26 @@ wait_for_completion_killable_timeout(str
>  EXPORT_SYMBOL(wait_for_completion_killable_timeout);
>  
>  /**
> + * wait_for_completion_long_io - waits for completion of a task
> + * @x:  holds the state of this particular completion
> + *
> + * This is like wait_for_completion_io, but it doesn't warn if the wait takes
> + * too long.
> + */
> +void wait_for_completion_long_io(struct completion *x)
> +{
> +	/* Prevent hang_check timer from firing at us during very long I/O */
> +	unsigned long timeout = sysctl_hung_task_timeout_secs * HZ / 2;
> +
> +	if (timeout)
> +		while (!wait_for_completion_io_timeout(x, timeout))
> +			;
> +	else
> +		wait_for_completion_io(x);
> +}
> +EXPORT_SYMBOL(wait_for_completion_long_io);

Urgh, why is it a sane thing to circumvent the hang check timer?