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timer: Try to survive timer callback preempt_count leak

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If a timer callback leaks preempt_count we currently assert a
BUG(). That makes it unnecessarily hard to retrieve information about
the problem especially on laptops and headless stations.

There is a decent chance to survive the preempt_count leak by
restoring the preempt_count to the value before the callback. That
allows in many cases to get valuable information about the root cause
of the problem.

We carried that fixup in preempt-rt for years and were able to decode
such wreckage quite a few times.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linux Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arjan van de Veen <arjan@infradead.org>
This commit is contained in:
Thomas Gleixner 2010-03-12 20:13:23 +01:00
parent 576da126a6
commit 802702e0c2
1 changed files with 9 additions and 3 deletions
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12
kernel/timer.c
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@ -982,9 +982,15 @@ static void call_timer_fn(struct timer_list *timer, void (*fn)(unsigned long),
lock_map_release(&lockdep_map);
if (preempt_count != preempt_count()) {
printk(KERN_ERR "timer: %pF preempt leak: %08x -> %08x\n",
fn, preempt_count, preempt_count());
BUG();
WARN_ONCE(1, "timer: %pF preempt leak: %08x -> %08x\n",
fn, preempt_count, preempt_count());
/*
* Restore the preempt count. That gives us a decent
* chance to survive and extract information. If the
* callback kept a lock held, bad luck, but not worse
* than the BUG() we had.
*/
preempt_count() = preempt_count;
}
}