From 95a442b8bd2242111f8d9331507031dee6bc54e4 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 1 Mar 2013 11:17:42 +0100 Subject: [PATCH 165/365] futex: Ensure lock/unlock symetry versus pi_lock and hash bucket lock In exit_pi_state_list() we have the following locking construct: spin_lock(&hb->lock); raw_spin_lock_irq(&curr->pi_lock); ... spin_unlock(&hb->lock); 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(+) diff --git a/kernel/futex.c b/kernel/futex.c index 068c2a971bf6..4b079bc02752 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -927,7 +927,9 @@ void exit_pi_state_list(struct task_struct *curr) * task still owns the PI-state: */ if (head->next != next) { + raw_spin_unlock_irq(&curr->pi_lock); spin_unlock(&hb->lock); + raw_spin_lock_irq(&curr->pi_lock); continue; } -- 2.28.0