linux-kernel - Re: [PATCH 4/4] posix-timers: turn it_signal into it

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Date:	Tue, 06 Sep 2011 17:39:56 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andi Kleen <ak@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 4/4] posix-timers: turn it_signal into it_valid flag

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.

diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index 4556182..4369747 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -502,14 +502,14 @@ static void k_itimer_rcu_free(struct rcu_head *head)
 #define IT_ID_NOT_SET	0
 static void release_posix_timer(struct k_itimer *tmr, int it_id_set)
 {
+	put_pid(tmr->it_pid);
+	sigqueue_free(tmr->sigq);
 	if (it_id_set) {
 		unsigned long flags;
 		spin_lock_irqsave(&idr_lock, flags);
 		idr_remove(&posix_timers_id, tmr->it_id);
 		spin_unlock_irqrestore(&idr_lock, flags);
 	}
-	put_pid(tmr->it_pid);
-	sigqueue_free(tmr->sigq);
 	call_rcu(&tmr->it.rcu, k_itimer_rcu_free);
 }
 



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