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Subject: Re: [PATCH 4/4] posix-timers: turn it_signal into it_valid flag
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Oleg Nesterov <oleg@redhat.com>, Andi Kleen <ak@linux.intel.com>,
        Andi Kleen <andi@firstfloor.org>, LKML <linux-kernel@vger.kernel.org>,
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Date: Tue, 06 Sep 2011 21:04:38 +0200
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Le mardi 06 septembre 2011 à 20:47 +0200, Thomas Gleixner a écrit :
> On Tue, 6 Sep 2011, Eric Dumazet wrote:
> 
> > Le mardi 06 septembre 2011 à 16:51 +0200, Oleg Nesterov a écrit :
> > > On 09/05, Andi Kleen wrote:
> > > >
> > > > > I forgot everything I knew about ->it_requeue_pending logic, but it
> > > > > seems to me that do_schedule_next_timer()->lock_timer() can find and
> > > > > lock successfully the wrong timer. Another thread can do timer_delete()
> > > > > and then re-create the timer with the same id.
> > > >
> > > > Do you mean after my patches or even before?
> > > 
> > > Ah, sorry for confusion.
> > > 
> > > Before. And after. IOW, I think this has nothing to do with your patches.
> > > 
> > 
> > Hmm, you mean following patch is needed ?
> > 
> > Before release of timer id to idr pool, we should make sure
> > do_schedule_next_timer() wont be called, or it could find another timer
> > reusing the just released id.
> 
> I don't see how that makes it sure. If the signal is queued, then it
> stays queued and the put_pid() has no effect either.

Indeed, this is a real old bug then...