linux-kernel - [tip:core/locking] locking/mutexes: Return false if task need_resched() in mutex_can_spin_on

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Date:	Tue, 11 Mar 2014 05:41:00 -0700
From:	tip-bot for Jason Low <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	peterz@...radead.org, jason.low2@...com, tglx@...utronix.de
Subject: [tip:core/locking] locking/mutexes:
  Return false if task need_resched() in mutex_can_spin_on_owner()

Commit-ID:  46af29e479cc0c1c63633007993af5292c2c3e75
Gitweb:     http://git.kernel.org/tip/46af29e479cc0c1c63633007993af5292c2c3e75
Author:     Jason Low <jason.low2@...com>
AuthorDate: Tue, 28 Jan 2014 11:13:12 -0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 11 Mar 2014 12:14:52 +0100

locking/mutexes: Return false if task need_resched() in mutex_can_spin_on_owner()

The mutex_can_spin_on_owner() function should also return false if the
task needs to be rescheduled to avoid entering the MCS queue when it
needs to reschedule.

Signed-off-by: Jason Low <jason.low2@...com>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Cc: Waiman.Long@...com
Cc: torvalds@...ux-foundation.org
Cc: tglx@...utronix.de
Cc: riel@...hat.com
Cc: akpm@...ux-foundation.org
Cc: davidlohr@...com
Cc: hpa@...or.com
Cc: andi@...stfloor.org
Cc: aswin@...com
Cc: scott.norton@...com
Cc: chegu_vinod@...com
Cc: paulmck@...ux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1390936396-3962-2-git-send-email-jason.low2@hp.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/locking/mutex.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 4f408be..e6d646b 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -166,6 +166,9 @@ static inline int mutex_can_spin_on_owner(struct mutex *lock)
 	struct task_struct *owner;
 	int retval = 1;
 
+	if (need_resched())
+		return 0;
+
 	rcu_read_lock();
 	owner = ACCESS_ONCE(lock->owner);
 	if (owner)
--
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