Commit 802702e0 authored Mar 12, 2010 by Thomas Gleixner

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 <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>

parent 576da126

kernel/timer.c

+9 −3

Original line number	Diff line number	Diff line
		@@ -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",
		WARN_ONCE(1, "timer: %pF preempt leak: %08x -> %08x\n",
		fn, preempt_count, preempt_count());
		BUG();
		/*
		* 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;
		}
		}