Commit-ID: 7f1b43936f0ecad14770634c021cf4a929aec74d
Gitweb: http://git.kernel.org/tip/7f1b43936f0ecad14770634c021cf4a929aec74d
Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
AuthorDate: Thu, 17 May 2012 21:19:46 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 6 Jun 2012 16:52:26 +0200
sched/rt: Fix lockdep annotation within find_lock_lowest_rq()
Roland Dreier reported spurious, hard to trigger lockdep warnings
within the scheduler - without any real lockup.
This bit gives us the right clue:
> [89945.640512] [<ffffffff8103fa1a>] double_lock_balance+0x5a/0x90
> [89945.640568] [<ffffffff8104c546>] push_rt_task+0xc6/0x290
if you look at that code you'll find the double_lock_balance() in
question is the one in find_lock_lowest_rq() [yay for inlining].
Now find_lock_lowest_rq() has a bug.. it fails to use
double_unlock_balance() in one exit path, if this results in a retry in
push_rt_task() we'll call double_lock_balance() again, at which point
we'll run into said lockdep confusion.
Reported-by: Roland Dreier <roland@xxxxxxxxxx>
Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1337282386.4281.77.camel@twins
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/sched/rt.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 2a4e8df..573e1ca 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1562,7 +1562,7 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
task_running(rq, task) ||
!task->on_rq)) {
- raw_spin_unlock(&lowest_rq->lock);
+ double_unlock_balance(rq, lowest_rq);
lowest_rq = NULL;
break;
}
--
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