signal: Remove no longer required irqsave/restore

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-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: bigeasy@linutronix.de
Link: https://lkml.kernel.org/r/20180525090507.22248-3-anna-maria@linutronix.de

diff --git a/kernel/signal.c b/kernel/signal.c
index 0f865d67415d54147b2cab487e6e51f0988b74c2..8d8a940422a8e0d7758a46fecff34b26782e1787 100644 (file)
--- 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;
 }