From: Davidlohr Bueso <dave@stgolabs>
Date: Thu, 10 Mar 2016 01:55:36 +0000 (-0800)
Subject: locking/csd_lock: Use smp_cond_acquire() in csd_lock_wait()
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=38460a2178d225b39ade5ac66586c3733391cf86;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git

locking/csd_lock: Use smp_cond_acquire() in csd_lock_wait()

We can micro-optimize this call and mildly relax the
barrier requirements by relying on ctrl + rmb, keeping
the acquire semantics. In addition, this is pretty much
the now standard for busy-waiting under such restraints.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dave@stgolabs.net
Link: http://lkml.kernel.org/r/1457574936-19065-3-git-send-email-dbueso@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---

diff --git a/kernel/smp.c b/kernel/smp.c
index 5099db15c5fb..300d29391e07 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -107,8 +107,7 @@ void __init call_function_init(void)
  */
 static __always_inline void csd_lock_wait(struct call_single_data *csd)
 {
-	while (smp_load_acquire(&csd->flags) & CSD_FLAG_LOCK)
-		cpu_relax();
+	smp_cond_acquire(!(csd->flags & CSD_FLAG_LOCK));
 }
 
 static __always_inline void csd_lock(struct call_single_data *csd)