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Message-ID: <20080910114401.GA220@tv-sign.ru>
Date: Wed, 10 Sep 2008 15:44:01 +0400
From: Oleg Nesterov <oleg@...sign.ru>
To: Roland McGrath <roland@...hat.com>
Cc: Ingo Molnar <mingo@...e.hu>, Frank Mayhar <fmayhar@...gle.com>,
linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
Alexey Dobriyan <adobriyan@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2.6.27-rc5] Fix itimer/many thread hang.
On 09/09, Roland McGrath wrote:
>
> > As for this particular function, it seems to me that ->signal == NULL
> > is not possible, no?
>
> The concern is to make sure that the timer tick path is always safe for a
> tick that hits during release_task(current) in exit_notify(). A timer tick
> there can come with current->signal == NULL. We just need to make sure one
> way or another that this is safe.
run_posix_cpu_timers() must check ->signal != NULL anyway. (The same for
other functions like account_group_user_time() which are called by the
timer tick).
Apart from the timer tick, "current" should not use this function after
exit_notify().
And, if tsk != current, ->signal must be pinned, this means it can't be NULL.
Perhaps I missed something, but imho this check is confusing and misleading.
However, this is just a minor detail even if I am right.
Oleg.
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