Commit a841796f11c9 ("signal: align __lock_task_sighand() irq disabling and
RCU") introduced a rcu read side critical section with interrupts
disabled. The changelog suggested that a better long-term fix would be "to
make rt_mutex_unlock() disable irqs when acquiring the rt_mutex structure's
->wait_lock".
This long-term fix has been made in commit b4abf91047cf ("rtmutex: Make
wait_lock irq safe") for a different reason.
Therefore revert commit a841796f11c9 ("signal: align >
__lock_task_sighand() irq disabling and RCU") as the interrupt disable
dance is not longer required.
The change was tested on the base of b4abf91047cf ("rtmutex: Make wait_lock
irq safe") with a four hour run of rcutorture scenario TREE03 with lockdep
enabled as suggested by Paul McKenney.
Signed-off-by: Anna-Maria Gleixner <anna-ma...@linutronix.de>
Acked-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
---
kernel/signal.c | 24 +++++++-----------------
1 file changed, 7 insertions(+), 17 deletions(-)
diff --git a/kernel/signal.c b/kernel/signal.c
index 9c33163a6165..19679ad77aa6 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1244,19 +1244,12 @@ struct sighand_struct *__lock_task_sighand(struct
task_struct *tsk,
{
struct sighand_struct *sighand;
+ rcu_read_lock();
for (;;) {
- /*
- * Disable interrupts early to avoid deadlocks.
- * See rcu_read_unlock() comment header for details.
- */
- local_irq_save(*flags);
- rcu_read_lock();
sighand = rcu_dereference(tsk->sighand);
- if (unlikely(sighand == NULL)) {
- rcu_read_unlock();
- local_irq_restore(*flags);
+ if (unlikely(sighand == NULL))
break;
- }
+
/*
* This sighand can be already freed and even reused, but
* we rely on SLAB_TYPESAFE_BY_RCU and sighand_ctor() which
@@ -1268,15 +1261,12 @@ struct sighand_struct *__lock_task_sighand(struct
task_struct *tsk,
* __exit_signal(). In the latter case the next iteration
* must see ->sighand == NULL.
*/
- spin_lock(&sighand->siglock);
- if (likely(sighand == tsk->sighand)) {
- rcu_read_unlock();
+ spin_lock_irqsave(&sighand->siglock, *flags);
+ if (likely(sighand == tsk->sighand))
break;
- }
- spin_unlock(&sighand->siglock);
- rcu_read_unlock();
- local_irq_restore(*flags);
+ spin_unlock_irqrestore(&sighand->siglock, *flags);
}
+ rcu_read_unlock();
return sighand;
}
--
2.15.1
