linux-kernel - [PATCH 1/2] locking/mutex: Further refactor mutex_spin_on

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Message-Id: <1428521960-5268-2-git-send-email-jason.low2@hp.com>
Date:	Wed,  8 Apr 2015 12:39:19 -0700
From:	Jason Low <jason.low2@...com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Aswin Chandramouleeswaran <aswin@...com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Jason Low <jason.low2@...com>
Subject: [PATCH 1/2] locking/mutex: Further refactor mutex_spin_on_owner()

Similar to what Linus suggested for rwsem_spin_on_owner(), in
mutex_spin_on_owner() instead of having while (true) and breaking
out of the spin loop on lock->owner != owner, we can have the loop
directly check for while (lock->owner == owner) to improve the
readability of the code.

Signed-off-by: Jason Low <jason.low2@...com>
---
 kernel/locking/mutex.c |   14 ++++----------
 1 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 16b2d3c..4cccea6 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -224,20 +224,14 @@ ww_mutex_set_context_slowpath(struct ww_mutex *lock,
 static noinline
 bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
 {
-	bool ret;
+	bool ret = true;
 
 	rcu_read_lock();
-	while (true) {
-		/* Return success when the lock owner changed */
-		if (lock->owner != owner) {
-			ret = true;
-			break;
-		}
-
+	while (lock->owner == owner) {
 		/*
 		 * Ensure we emit the owner->on_cpu, dereference _after_
-		 * checking lock->owner still matches owner, if that fails,
-		 * owner might point to free()d memory, if it still matches,
+		 * checking lock->owner still matches owner. If that fails,
+		 * owner might point to freed memory. If it still matches,
 		 * the rcu_read_lock() ensures the memory stays valid.
 		 */
 		barrier();
-- 
1.7.2.5

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