[tip:locking/core] rtmutex: Plug preempt count leak in rt_mutex_futex_unlock()

[tip-bot for Mike Galbraith]

Commit-ID:  def34eaae5ce04b324e48e1bfac873091d945213
Gitweb: http://git.kernel.org/tip/def34eaae5ce04b324e48e1bfac873091d945213
Author: Mike Galbraith 
AuthorDate: Wed, 5 Apr 2017 10:08:27 +0200
Committer:  Thomas Gleixner 
CommitDate: Wed, 5 Apr 2017 16:59:37 +0200

rtmutex: Plug preempt count leak in rt_mutex_futex_unlock()

mark_wakeup_next_waiter() already disables preemption, doing so again
leaves us with an unpaired preempt_disable().

Fixes: 2a1c60299406 ("rtmutex: Deboost before waking up the top waiter")
Signed-off-by: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: xlp...@redhat.com
Cc: rost...@goodmis.org
Link: http://lkml.kernel.org/r/1491379707.6538.2.ca...@gmx.de
Signed-off-by: Thomas Gleixner 
---
 kernel/locking/rtmutex.c | 10 +-
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 0e641eb..b955094 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1581,13 +1581,13 @@ bool __sched __rt_mutex_futex_unlock(struct rt_mutex 
*lock,
return false; /* done */
}
 
-   mark_wakeup_next_waiter(wake_q, lock);
/*
-* We've already deboosted, retain preempt_disabled when dropping
-* the wait_lock to avoid inversion until the wakeup. Matched
-* by rt_mutex_postunlock();
+* We've already deboosted, mark_wakeup_next_waiter() will
+* retain preempt_disabled when we drop the wait_lock, to
+* avoid inversion prior to the wakeup.  preempt_disable()
+* therein pairs with rt_mutex_postunlock().
 */
-   preempt_disable();
+   mark_wakeup_next_waiter(wake_q, lock);
 
return true; /* call postunlock() */
 }

[tip:locking/core] rtmutex: Plug preempt count leak in rt_mutex_futex_unlock()

[tip-bot for Mike Galbraith]

Commit-ID:  def34eaae5ce04b324e48e1bfac873091d945213
Gitweb: http://git.kernel.org/tip/def34eaae5ce04b324e48e1bfac873091d945213
Author: Mike Galbraith 
AuthorDate: Wed, 5 Apr 2017 10:08:27 +0200
Committer:  Thomas Gleixner 
CommitDate: Wed, 5 Apr 2017 16:59:37 +0200

rtmutex: Plug preempt count leak in rt_mutex_futex_unlock()

mark_wakeup_next_waiter() already disables preemption, doing so again
leaves us with an unpaired preempt_disable().

Fixes: 2a1c60299406 ("rtmutex: Deboost before waking up the top waiter")
Signed-off-by: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: xlp...@redhat.com
Cc: rost...@goodmis.org
Link: http://lkml.kernel.org/r/1491379707.6538.2.ca...@gmx.de
Signed-off-by: Thomas Gleixner 
---
 kernel/locking/rtmutex.c | 10 +-
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 0e641eb..b955094 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1581,13 +1581,13 @@ bool __sched __rt_mutex_futex_unlock(struct rt_mutex 
*lock,
return false; /* done */
}
 
-   mark_wakeup_next_waiter(wake_q, lock);
/*
-* We've already deboosted, retain preempt_disabled when dropping
-* the wait_lock to avoid inversion until the wakeup. Matched
-* by rt_mutex_postunlock();
+* We've already deboosted, mark_wakeup_next_waiter() will
+* retain preempt_disabled when we drop the wait_lock, to
+* avoid inversion prior to the wakeup.  preempt_disable()
+* therein pairs with rt_mutex_postunlock().
 */
-   preempt_disable();
+   mark_wakeup_next_waiter(wake_q, lock);
 
return true; /* call postunlock() */
 }