[tip:locking/core] locking/qspinlock: Use smp_cond_acquire() in pending code

From: tip-bot for Waiman Long
Date: Mon Feb 29 2016 - 06:21:40 EST

Commit-ID: cb037fdad6772df2d49fe61c97d7c0d8265bc918
Gitweb: http://git.kernel.org/tip/cb037fdad6772df2d49fe61c97d7c0d8265bc918
Author: Waiman Long <Waiman.Long@xxxxxxx>
AuthorDate: Thu, 10 Dec 2015 15:17:44 -0500
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 29 Feb 2016 10:02:42 +0100

locking/qspinlock: Use smp_cond_acquire() in pending code

The newly introduced smp_cond_acquire() was used to replace the
slowpath lock acquisition loop. Similarly, the new function can also
be applied to the pending bit locking loop. This patch uses the new
function in that loop.

Signed-off-by: Waiman Long <Waiman.Long@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Douglas Hatch <doug.hatch@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Scott J Norton <scott.norton@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1449778666-13593-1-git-send-email-Waiman.Long@xxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
kernel/locking/qspinlock.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 393d187..ce2f75e 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -358,8 +358,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
* sequentiality; this is because not all clear_pending_set_locked()
* implementations imply full barriers.
- while ((val = smp_load_acquire(&lock->val.counter)) & _Q_LOCKED_MASK)
- cpu_relax();
+ smp_cond_acquire(!(atomic_read(&lock->val) & _Q_LOCKED_MASK));

* take ownership and clear the pending bit.
@@ -435,7 +434,7 @@ queue:
* The PV pv_wait_head_or_lock function, if active, will acquire
* the lock and return a non-zero value. So we have to skip the
- * smp_load_acquire() call. As the next PV queue head hasn't been
+ * smp_cond_acquire() call. As the next PV queue head hasn't been
* designated yet, there is no way for the locked value to become
* _Q_SLOW_VAL. So both the set_locked() and the
* atomic_cmpxchg_relaxed() calls will be safe.
@@ -466,7 +465,7 @@ locked:
- * The smp_load_acquire() call above has provided the necessary
+ * The smp_cond_acquire() call above has provided the necessary
* acquire semantics required for locking. At most two
* iterations of this loop may be ran.