linux-kernel - Re: [GIT PULL] core/locking changes for v3.2

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Message-ID: <CA+55aFw84RRBxT0QwDT6dg94OqreS8vwMq7Qog+o0QXqR8vgEA@mail.gmail.com>
Date:	Wed, 26 Oct 2011 16:21:51 +0200
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] core/locking changes for v3.2

On Wed, Oct 26, 2011 at 3:25 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
> Note, you will get a conflict in kernel/posix-cpu-timers.c, which i
> resolved in -tip the following way:
>
>        raw_spin_lock_irqsave(&cputimer->lock, flags);
>        if (!cputimer->running) {
>                cputimer->running = 1;
>                /*
>                 * The POSIX timer interface allows for absolute time expiry
>                 * values through the TIMER_ABSTIME flag, therefore we have
>                 * to synchronize the timer to the clock every time we start
>                 * it.
>                 */
>                thread_group_cputime(tsk, &sum);
>                update_gt_cputime(&cputimer->cputime, &sum);
>        }
>        *times = cputimer->cputime;
>        raw_spin_unlock_irqrestore(&cputimer->lock, flags);

That seems like a completely bogus resolution. You are re-introducing
the incorrect ABBA nesting of cputimer->lock and rq->lock, and
basically undoing commit bcd5cff7216f.

So I did that resolve differently in a way that I believe is correct.
But please do check the end result out. Peter?

                   Linus
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