[PATCH 01/11] locking/mutex: Dont assume TASK_RUNNING

Peter Zijlstra
2014-09-24T08:36:31Z

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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>
---
kernel/locking/mutex.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -378,8 +378,14 @@ static bool mutex_optimistic_spin(struct
* 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;
}