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From: tip-bot for Anna-Maria Gleixner <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: mingo@kernel.org, ebiederm@xmission.com,
	anna-maria@linutronix.de, hpa@zytor.com,
	paulmck@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
	tglx@linutronix.de
Subject: [tip:core/urgent] signal: Remove no longer required irqsave/restore
Date: Sat, 9 Jun 2018 21:19:14 -0700	[thread overview]
Message-ID: <tip-59dc6f3c6d81c0c4379025c4eb56919391d62b67@git.kernel.org> (raw)
In-Reply-To: <20180525090507.22248-3-anna-maria@linutronix.de>

Commit-ID:  59dc6f3c6d81c0c4379025c4eb56919391d62b67
Gitweb:     https://git.kernel.org/tip/59dc6f3c6d81c0c4379025c4eb56919391d62b67
Author:     Anna-Maria Gleixner <anna-maria@linutronix.de>
AuthorDate: Fri, 25 May 2018 11:05:07 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sun, 10 Jun 2018 06:14:01 +0200

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

---
 kernel/signal.c | 24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 0f865d67415d..8d8a940422a8 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;
 }

  reply	other threads:[~2018-06-10  4:19 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-25  9:05 [PATCH v2 0/2] rtmutex wait_lock is irq safe Anna-Maria Gleixner
2018-05-25  9:05 ` [PATCH v2 1/2] rcu: Update documentation of rcu_read_unlock() Anna-Maria Gleixner
2018-05-25 14:19   ` Paul E. McKenney
2018-05-28  9:49     ` Anna-Maria Gleixner
2018-06-10  4:18   ` [tip:core/urgent] " tip-bot for Anna-Maria Gleixner
2018-05-25  9:05 ` [PATCH v2 2/2] signal: Remove no longer required irqsave/restore Anna-Maria Gleixner
2018-06-10  4:19   ` tip-bot for Anna-Maria Gleixner [this message]
2018-05-25 20:02 ` [PATCH v2 0/2] rtmutex wait_lock is irq safe Eric W. Biederman
  -- strict thread matches above, loose matches on Subject: below --
2018-05-04 14:40 [PATCH] kernel/signal: Remove no longer required irqsave/restore Sebastian Andrzej Siewior
2018-06-07 20:21 ` [tip:core/urgent] signal: " tip-bot for Anna-Maria Gleixner

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