From e42f678a0237f84f0004fbaf0fad0b844751eadd Mon Sep 17 00:00:00 2001
From: Davidlohr Bueso <dave@stgolabs.net>
Date: Tue, 6 Jan 2015 11:45:05 -0800
Subject: [PATCH] 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@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1420573509-24774-3-git-send-email-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.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 b042ea57bbea..6db3d0dea6da 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;