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authorThomas Gleixner <tglx@linutronix.de>2010-03-12 20:13:23 +0100
committerThomas Gleixner <tglx@linutronix.de>2010-03-12 22:40:44 +0100
commit802702e0c2618465b813242d4dfee6a233ba0beb (patch)
treee21c74065e82a77c45c4f815c626fbafc7fff469 /kernel/timer.c
parent576da126a6c7364d70dfd58d0bbe43d05cf5859f (diff)
downloadlwn-802702e0c2618465b813242d4dfee6a233ba0beb.tar.gz
lwn-802702e0c2618465b813242d4dfee6a233ba0beb.zip
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>
Diffstat (limited to 'kernel/timer.c')
-rw-r--r--kernel/timer.c12
1 files 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;
}
}