Messages in this thread Patch in this message | | | Subject | [PATCH -rt] Remove false BUG_ON from rtmutex.c | From | Steven Rostedt <> | Date | Tue, 18 Apr 2006 10:13:10 -0400 |
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Ingo,
Here's a patch to remove the BUG_ON in rtmutex.c. I previously showed that the condition in that particular BUG_ON can legitimately be the case.
Once again, if you have processes A, B, C, D, and E holding the following locks in this scenario:
L1 <=blocks= A <=owns= L2 <=blocks= B <=owns= L4 <=blocks= D <=owns= L3 <=blocks= C <=owns= L5 <=blocks= E
Where the priorities of these tasks are
B,C < A < D = E
B and C are less than A and A is less than D and E where D and E are equal (actually it probably works when D and E are not equal too).
As D and E climb the chain, there's a very slight race condition that could allow for the condition in the offending BUG_ON to be true.
This patch removes that BUG_ON.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Index: linux-2.6.16-rt16/kernel/rtmutex.c =================================================================== --- linux-2.6.16-rt16.orig/kernel/rtmutex.c 2006-04-17 14:49:43.000000000 -0400 +++ linux-2.6.16-rt16/kernel/rtmutex.c 2006-04-18 09:57:54.000000000 -0400 @@ -232,10 +232,8 @@ static int rt_mutex_adjust_prio_chain(ta * When deadlock detection is off then we check, if further * priority adjustment is necessary. */ - if (!detect_deadlock && waiter->list_entry.prio == task->prio) { - BUG_ON(waiter->pi_list_entry.prio != waiter->list_entry.prio); + if (!detect_deadlock && waiter->list_entry.prio == task->prio) goto out_unlock_pi; - } lock = waiter->lock; if (!spin_trylock(&lock->wait_lock)) {
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