From: Steven Rostedt <[email protected]>
The condition in that particular BUG_ON can legitimately be the
case, 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.
Signed-off-by: Steven Rostedt <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
kernel/rtmutex.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
Index: linux-2.6.17-rc1-mm3/kernel/rtmutex.c
===================================================================
--- linux-2.6.17-rc1-mm3.orig/kernel/rtmutex.c
+++ linux-2.6.17-rc1-mm3/kernel/rtmutex.c
@@ -209,10 +209,8 @@ 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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