linux-kernel - Re: [patch 1/6] posix-cpu-timers: Always clear head pointer on dequeue

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Date:   Thu, 5 Sep 2019 17:49:35 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        syzbot+55acd54b57bb4b3840a4@...kaller.appspotmail.com
Subject: Re: [patch 1/6] posix-cpu-timers: Always clear head pointer on
 dequeue

On Thu, Sep 05, 2019 at 02:03:40PM +0200, Thomas Gleixner wrote:
> The head pointer in struct cpu_timer is checked to be NULL in
> posix_cpu_timer_del() when the delete raced with the exit cleanup. The
> works correctly as long as the timer is actually dequeued via
> posix_cpu_timers_exit*().
> 
> But if the timer was dequeued due to expiry the head pointer is still set
> and triggers the warning.
> 
> In fact keeping the head pointer around after any dequeue is pointless as
> is has no meaning at all after that.
> 
> Clear the head pointer always on dequeue and remove the unused requeue
> function while at it.
> 
> Fixes: 60bda037f1dd ("posix-cpu-timers: Utilize timerqueue for storage")
> Reported-by: syzbot+55acd54b57bb4b3840a4@...kaller.appspotmail.com
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Reviewed-by: Frederic Weisbecker <frederic@...nel.org>