blob: 70e3601e1aa81df42fdc0b46b286c530014a4012 [file] [log] [blame]
From: Thomas Gleixner <>
Date: Fri, 1 Mar 2013 11:17:42 +0100
Subject: futex: Ensure lock/unlock symetry versus pi_lock and hash bucket lock
In exit_pi_state_list() we have the following locking construct:
In !RT this works, but on RT the migrate_enable() function which is
called from spin_unlock() sees atomic context due to the held pi_lock
and just decrements the migrate_disable_atomic counter of the
task. Now the next call to migrate_disable() sees the counter being
negative and issues a warning. That check should be in
migrate_enable() already.
Fix this by dropping pi_lock before unlocking hb->lock and reaquire
pi_lock after that again. This is safe as the loop code reevaluates
head again under the pi_lock.
Reported-by: Yong Zhang <>
Signed-off-by: Thomas Gleixner <>
Signed-off-by: Sebastian Andrzej Siewior <>
kernel/futex.c | 2 ++
1 file changed, 2 insertions(+)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -911,7 +911,9 @@ void exit_pi_state_list(struct task_stru
* task still owns the PI-state:
if (head->next != next) {
+ raw_spin_unlock_irq(&curr->pi_lock);
+ raw_spin_lock_irq(&curr->pi_lock);