linux-kernel - [PATCH 2/6] locking/mutex: Move mcs related comments to proper location

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Date:	Tue,  6 Jan 2015 11:45:05 -0800
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 2/6] locking/mutex: Move mcs related comments to proper location

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

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 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;
 
-- 
2.1.2

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