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IEEE1284: Use del_timer_sync in parport_wait_event

PATCH In review Michael Buesch 2 participants 2 messages Nov 30, 2008 – Dec 3, 2008 Parallel port

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Michael Buesch

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PATCH 1/1 IEEE1284: Use del_timer_sync in parport_wait_event

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 <[email protected]>

---

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.

drivers/parport/ieee1284.c +1 -1
Index: linux-2.6/drivers/parport/ieee1284.c
===================================================================
@@ -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;
Signature · 1 line
Greetings Michael.
#1 lore raw
Quoted 8 lines · On Sun, 30 Nov 2008 21:20:49 +0100 Michael Buesch <[email protected]> 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 <[email protected]>

---

Quoted 9 lines

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.

drivers/parport/ieee1284.c int parport_wait_event (struct parport * · line 89

Quoted 11 lines

===================================================================

drivers/parport/ieee1284.c +1 -1
@@ -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() :)