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Date: Fri, 15 Feb 2013 15:53:23 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Mandeep Singh Baines <msb@chromium.org>
Cc: linux-kernel@vger.kernel.org, Tejun Heo <tj@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Rafael J. Wysocki" <rjw@sisk.pl>, Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH 3/5] coredump: cleanup the waiting for coredump_finish
	code
Message-ID: <20130215145323.GA30829@redhat.com>
References: <1360885096-21207-1-git-send-email-msb@chromium.org> <1360885096-21207-3-git-send-email-msb@chromium.org>
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On 02/14, Mandeep Singh Baines wrote:
>
> Replace the for loop with a simple if.

Why?

> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -479,12 +479,9 @@ static void exit_mm(struct task_struct * tsk)
>  		if (atomic_dec_and_test(&core_state->nr_threads))
>  			complete(&core_state->startup);
>
> -		for (;;) {
> -			set_task_state(tsk, TASK_UNINTERRUPTIBLE);
> -			if (!self.task) /* see coredump_finish() */
> -				break;
> +		set_task_state(tsk, TASK_UNINTERRUPTIBLE);
> +		if (self.task) /* see coredump_finish() */
>  			schedule();
> -		}

If you think we should not worry about spurious wakeups you can simplify
this code even more, you do not need mb() to set TASK_UNINTERRUPTIBLE
(just move it before dec_and_test), you do not need "if (self.task)",
you do not need __set_task_state(tsk, TASK_RUNNING).

But I think we should always worry, so why?

Oleg.