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    SubjectRe: [PATCH] IEEE1284: Use del_timer_sync in parport_wait_event
    On Sun, 30 Nov 2008 21:20:49 +0100
    Michael Buesch <mb@bu3sch.de> wrote:

    > Use del_timer_sync() instead of del_timer() to make sure
    > the timer won't be running when we return from parport_wait_event(),
    > because this would crash due to destruction of timer_list.
    >
    > Signed-off-by: Michael Buesch <mb@bu3sch.de>
    >
    > ---
    >
    > This is completely untested and just based on a code review.
    > Just think about the following sequence of events:
    > add_timer.
    > down_interruptible is interrupted by a signal.
    > We enter the timer callback handler on another CPU.
    > del_timer, but the timer callback is still running.
    > Return from parport_wait_even, which destroys the automatic variable "timer"
    > while the callback is running on another CPU.
    >

    Yes, I agree.

    > ===================================================================
    > --- linux-2.6.orig/drivers/parport/ieee1284.c 2008-10-24 21:08:12.000000000 +0200
    > +++ linux-2.6/drivers/parport/ieee1284.c 2008-11-30 21:09:25.000000000 +0100
    > @@ -84,7 +84,7 @@ int parport_wait_event (struct parport *
    >
    > add_timer (&timer);
    > ret = down_interruptible (&port->physport->ieee1284.irq);
    > - if (!del_timer (&timer) && !ret)
    > + if (!del_timer_sync (&timer) && !ret)
    > /* Timed out. */
    > ret = 1;

    Please fix checkpatch errors when altering code. This function is
    already a mismash of correct and incorrect styles - we might as well
    increase the correctness density.

    What we really want in this function is down_interruptible_timeout().
    afaict we have all the infrastructure in place to implement that, but
    nobody has typed

    static noinline int __sched
    __down_interruptible_timeout(struct semaphore *sem, long jiffies)
    {
    return __down_common(sem, TASK_INTERRUPTIBLE, jiffies);
    }

    and then tested it.

    Or convert the whole thing to mutexes and write
    mutex_lock_interruptible_timeout() :)



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