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signal: Remove no longer required irqsave/restore

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Commit a841796f11 ("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 b4abf91047 ("rtmutex: Make
wait_lock irq safe") for a different reason.

Therefore revert commit a841796f11 ("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 b4abf91047 ("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
This commit is contained in:
Anna-Maria Gleixner 2018-05-25 11:05:07 +02:00 committed by Thomas Gleixner
parent ec84b27f9b
commit 59dc6f3c6d
1 changed files with 7 additions and 17 deletions
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24
kernel/signal.c
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@ -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;
}