[tip:sched/core] locking/mutex: Don't assume TASK_RUNNING

tip-bot for Peter Zijlstra
2014-10-28T11:10:28Z

Commit-ID: 6f942a1f264e875c5f3ad6f505d7b500a3e7fa82
Gitweb: http://git.kernel.org/tip/6f942a1f264e875c5f3ad6f505d7b500a3e7fa82
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Wed, 24 Sep 2014 10:18:46 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 28 Oct 2014 10:55:08 +0100

locking/mutex: Don't assume TASK_RUNNING

We're going to make might_sleep() test for TASK_RUNNING, because
blocking without TASK_RUNNING will destroy the task state by setting
it to TASK_RUNNING.

There are a few occasions where its 'valid' to call blocking
primitives (and mutex_lock in particular) and not have TASK_RUNNING,
typically such cases are right before we set TASK_RUNNING anyhow.

Robustify the code by not assuming this; this has the beneficial side
effect of allowing optional code emission for fixing the above
might_sleep() false positives.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: tglx@linutronix.de
Cc: ilya.dryomov@inktank.com
Cc: umgwanakikbuti@gmail.com
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140924082241.988560063@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/locking/mutex.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index dadbf88..4541951 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -378,8 +378,14 @@ done:
* reschedule now, before we try-lock the mutex. This avoids getting
* scheduled out right after we obtained the mutex.
*/
- if (need_resched())
+ if (need_resched()) {
+ /*
+ * We _should_ have TASK_RUNNING here, but just in case
+ * we do not, make it so, otherwise we might get stuck.
+ */
+ __set_current_state(TASK_RUNNING);
schedule_preempt_disabled();
+ }

return false;
}