Messages in this thread Patch in this message | | | From | Nick Piggin <> | Subject | [rfc] "improve" preempt debugging | Date | Tue, 30 Sep 2008 20:50:27 +1000 |
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Hi, don't know if you really like this patch or not, but it helped me out with a problem I recently had....
Basically, when the kernel lock is held, then preempt_count underflow does not get detected until it is released which may be a long time (and arbitrarily, eg at different points it may be rescheduled). If the bkl is released at schedule, the resulting output is actually fairly cryptic...
With any other lock that elevates preempt_count, it is illegal to schedule under it (which would get found pretty quickly). bkl allows scheduling with preempt_count elevated, which makes underflows hard to debug.
Index: linux-2.6/kernel/sched.c =================================================================== --- linux-2.6.orig/kernel/sched.c 2008-09-30 11:32:56.000000000 +1000 +++ linux-2.6/kernel/sched.c 2008-09-30 11:38:18.000000000 +1000 @@ -4305,7 +4305,7 @@ void __kprobes sub_preempt_count(int val /* * Underflow? */ - if (DEBUG_LOCKS_WARN_ON(val > preempt_count())) + if (DEBUG_LOCKS_WARN_ON(val > preempt_count() - (!!kernel_locked()))) return; /* * Is the spinlock portion underflowing?
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