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* [PATCH v2 0/2] rtmutex wait_lock is irq safe
@ 2018-05-25  9:05 Anna-Maria Gleixner
  2018-05-25  9:05 ` [PATCH v2 1/2] rcu: Update documentation of rcu_read_unlock() Anna-Maria Gleixner
                   ` (2 more replies)
  0 siblings, 3 replies; 9+ messages in thread
From: Anna-Maria Gleixner @ 2018-05-25  9:05 UTC (permalink / raw)
  To: linux-kernel; +Cc: tglx, bigeasy, paulmck, ebiederm, Anna-Maria Gleixner

Since commit b4abf91047cf ("rtmutex: Make wait_lock irq safe") the rtmutex
wait_lock is irq safe. Therefore the irqsave/restore in kernel/signal is no
longer required (see Patch 2/2). During discussions about v1 of this patch,
Eric Biederman noticed, that there is a no longer valid rcu_read_unlock()
documentation.

Therefore sending a short queue: fixing first the documentation of
rcu_read_unlock() and afterwards removing irqsave/restore in kernel/signal.

v1..v2:

 - Add new patch updating rcu documentation as suggested by Eric Biederman
 - Udpate commit message of kernel/signal patch

Thanks,

	Anna-Maria


Anna-Maria Gleixner (2):
  rcu: Update documentation of rcu_read_unlock()
  signal: Remove no longer required irqsave/restore

 include/linux/rcupdate.h |  4 +---
 kernel/signal.c          | 24 +++++++-----------------
 2 files changed, 8 insertions(+), 20 deletions(-)

-- 
2.15.1

^ permalink raw reply	[flat|nested] 9+ messages in thread
* [PATCH] kernel/signal: Remove no longer required irqsave/restore
@ 2018-05-04 14:40 Sebastian Andrzej Siewior
  2018-06-07 20:21 ` [tip:core/urgent] signal: " tip-bot for Anna-Maria Gleixner
  0 siblings, 1 reply; 9+ messages in thread
From: Sebastian Andrzej Siewior @ 2018-05-04 14:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: tglx, Eric W. Biederman, Paul E . McKenney, Anna-Maria Gleixner,
	Sebastian Andrzej Siewior

From: Anna-Maria Gleixner <anna-maria@linutronix.de>

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 4abf91047cf ("rtmutex: Make >
wait_lock irq safe") for different reason.

Therefore revert commit a841796f11c9 ("signal: align >
__lock_task_sighand() irq disabling and RCU") as the interrupt disable
dance is not longer required.

Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/signal.c | 24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index c6e4c83dc090..16b87c54d027 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;
 }
-- 
2.17.0

^ permalink raw reply	[flat|nested] 9+ messages in thread

end of thread, other threads:[~2018-06-10  4:19 UTC | newest]

Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
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:core/urgent] " tip-bot for Anna-Maria Gleixner
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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