Commit 59dc6f3c authored May 25, 2018 by Anna-Maria Gleixner Committed by Thomas Gleixner Jun 10, 2018

signal: Remove no longer required irqsave/restore



Commit a841796f ("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 b4abf910 ("rtmutex: Make
wait_lock irq safe") for a different reason.

Therefore revert commit a841796f ("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 b4abf910 ("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

parent ec84b27f

kernel/signal.c

+7 −17

Original line number	Diff line number	Diff line
		@@ -1244,19 +1244,12 @@ struct sighand_struct __lock_task_sighand(struct task_struct tsk,
		{
		struct sighand_struct *sighand;

		for (;;) {
		/*
		* Disable interrupts early to avoid deadlocks.
		* See rcu_read_unlock() comment header for details.
		*/
		local_irq_save(*flags);
		rcu_read_lock();
		for (;;) {
		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_irqrestore(&sighand->siglock, *flags);
		}
		spin_unlock(&sighand->siglock);
		rcu_read_unlock();
		local_irq_restore(*flags);
		}

		return sighand;
		}

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