linux-kernel - [tip:locking/core] locking/mutex: Move MCS related comments to proper location

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Date:	Wed, 14 Jan 2015 11:18:54 -0800
From:	tip-bot for Davidlohr Bueso <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, peterz@...radead.org,
	torvalds@...ux-foundation.org, paulmck@...ux.vnet.ibm.com,
	tglx@...utronix.de, dbueso@...e.de, mingo@...nel.org,
	dave@...olabs.net
Subject: [tip:locking/core] locking/mutex:
  Move MCS related comments to proper location

Commit-ID:  e42f678a0237f84f0004fbaf0fad0b844751eadd
Gitweb:     http://git.kernel.org/tip/e42f678a0237f84f0004fbaf0fad0b844751eadd
Author:     Davidlohr Bueso <dave@...olabs.net>
AuthorDate: Tue, 6 Jan 2015 11:45:05 -0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 14 Jan 2015 15:07:22 +0100

locking/mutex: Move MCS related comments to proper location

It serves much better if the comments are right before the osq_lock() call.
Also delete a useless comment.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: http://lkml.kernel.org/r/1420573509-24774-3-git-send-email-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/locking/mutex.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index b042ea5..6db3d0d 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -193,17 +193,6 @@ ww_mutex_set_context_fastpath(struct ww_mutex *lock,
 
 
 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
-/*
- * In order to avoid a stampede of mutex spinners from acquiring the mutex
- * more or less simultaneously, the spinners need to acquire a MCS lock
- * first before spinning on the owner field.
- *
- */
-
-/*
- * Mutex spinning code migrated from kernel/sched/core.c
- */
-
 static inline bool owner_running(struct mutex *lock, struct task_struct *owner)
 {
 	if (lock->owner != owner)
@@ -307,6 +296,11 @@ static bool mutex_optimistic_spin(struct mutex *lock,
 	if (!mutex_can_spin_on_owner(lock))
 		goto done;
 
+	/*
+	 * In order to avoid a stampede of mutex spinners trying to
+	 * acquire the mutex all at once, the spinners need to take a
+	 * MCS (queued) lock first before spinning on the owner field.
+	 */
 	if (!osq_lock(&lock->osq))
 		goto done;
 
--
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