From 802702e0c2618465b813242d4dfee6a233ba0beb Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 12 Mar 2010 20:13:23 +0100 Subject: [PATCH] timer: Try to survive timer callback preempt_count leak 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 Cc: Linux Torvalds Cc: Andrew Morton Cc: Arjan van de Veen --- kernel/timer.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/kernel/timer.c b/kernel/timer.c index 45229694dc6a..7e12e7bc7ce6 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -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; } }