linux-kernel - Re: [PATCH 1/2] posix-cpu-timers: avoid do_sys_times() races with __exit

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Date:	Fri, 12 Jun 2009 09:09:58 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] posix-cpu-timers: avoid do_sys_times() races with
 __exit_signal()

On Fri, 2009-06-12 at 08:49 +0200, Stanislaw Gruszka wrote:
> Protect thread_group_cputime() call by siglock, to avoid possible (but
> to be honest - very improbable) double times accounting of exiting task.
> This is revert of commit 2b5fe6de58276d0b5a7c884d5dbfc300ca47db78
> "thread_group_cputime: move a couple of callsites outside of ->siglock",
> but implementation of thread_group_cputime() was different then.

Would be nice to have a description of exactly how you'd end up
accounting twice (and thus how this patch fixes it).

> Signed-off-by: Stanislaw Gruszka <sgruszka@...hat.com>
> ---
>  kernel/sys.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/sys.c b/kernel/sys.c
> index e7998cf..0805d08 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -913,8 +913,8 @@ void do_sys_times(struct tms *tms)
>  	struct task_cputime cputime;
>  	cputime_t cutime, cstime;
>  
> -	thread_group_cputime(current, &cputime);
>  	spin_lock_irq(&current->sighand->siglock);
> +	thread_group_cputime(current, &cputime);
>  	cutime = current->signal->cutime;
>  	cstime = current->signal->cstime;
>  	spin_unlock_irq(&current->sighand->siglock);

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