From: Ingo Molnar <mingo@elte.hu>
To: Tejun Huh <tejun@aratech.co.kr>
Cc: linux-kernel@vger.kernel.org, Linus Torvalds <torvalds@osdl.org>,
Andrew Morton <akpm@digeo.com>
Subject: Re: [PATCH] Race condition in del_timer_sync (2.5)
Date: Tue, 2 Sep 2003 08:33:50 +0200 (CEST) [thread overview]
Message-ID: <Pine.LNX.4.56.0309020820330.3654@localhost.localdomain> (raw)
In-Reply-To: <20030902025927.GA12121@atj.dyndns.org>
On Tue, 2 Sep 2003, Tejun Huh wrote:
> This patch fixes a race between del_timer_sync and recursive timers.
> Current implementation allows the value of timer->base that is used for
> timer_pending test to be fetched before finishing running_timer test, so
> it's possible for a recursive time to be pending after del_timer_sync.
> Adding smp_rmb before timer_pending removes the race.
good catch. Have you ever trigger this bug, or did you find it via code
review?
just to explore the scope of this problem a bit more: at first glance all
other timer_pending() uses seem to be safe. del_timer_sync()'s
timer_pending() use is special, because it's next to the ->running_timer
check without any barriers inbetween - so we could indeed in theory end up
with having the two reads reordered and a freshly added timer (on another
CPU) not being recognized properly. Also, this is the only timer API call
that guarantees the complete stopping of a timer.
Ingo
next prev parent reply other threads:[~2003-09-02 6:43 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-09-02 2:59 [PATCH] Race condition in del_timer_sync (2.5) Tejun Huh
2003-09-02 6:33 ` Ingo Molnar [this message]
2003-09-02 7:54 ` Tejun Huh
2003-09-02 7:55 ` Linus Torvalds
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