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SubjectRe: [GIT PULL] core/locking changes for v3.2

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Wed, Oct 26, 2011 at 3:25 PM, Ingo Molnar <mingo@elte.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.

oh, i quoted the resolution from the pre-ABBA-fix tree :-/

The one in tip:master is:

void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
{
struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
struct task_cputime sum;
unsigned long flags;

if (!cputimer->running) {
/*
* 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);
raw_spin_lock_irqsave(&cputimer->lock, flags);
cputimer->running = 1;
update_gt_cputime(&cputimer->cputime, &sum);
} else
raw_spin_lock_irqsave(&cputimer->lock, flags);
*times = cputimer->cputime;
raw_spin_unlock_irqrestore(&cputimer->lock, flags);
}

Good thing you double checked it.

Thanks,

Ingo
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