[tip:locking/core] locking/x86: Use mb() around clflush()

["tip-bot for Michael S. Tsirkin" <tipbot@zytor.com>]

Commit-ID:  ca59809ff6d572ae58fc6bedf7500f5a60fdbd64
Gitweb:     http://git.kernel.org/tip/ca59809ff6d572ae58fc6bedf7500f5a60fdbd64
Author:     Michael S. Tsirkin <mst@redhat.com>
AuthorDate: Thu, 28 Jan 2016 19:02:51 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 29 Jan 2016 09:40:10 +0100

locking/x86: Use mb() around clflush()

The following commit:

  f8e617f4582995f ("sched/idle/x86: Optimize unnecessary mwait_idle() resched IPIs")

adds memory barriers around clflush(), but this seems wrong for UP since
barrier() has no effect on clflush().  We really want MFENCE, so switch
to mb() instead.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <bitbucket@online.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: virtualization <virtualization@lists.linux-foundation.org>
Link: http://lkml.kernel.org/r/1453921746-16178-5-git-send-email-mst@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/process.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 9f7c21c..9decee2 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -418,9 +418,9 @@ static void mwait_idle(void)
 	if (!current_set_polling_and_test()) {
 		trace_cpu_idle_rcuidle(1, smp_processor_id());
 		if (this_cpu_has(X86_BUG_CLFLUSH_MONITOR)) {
-			smp_mb(); /* quirk */
+			mb(); /* quirk */
 			clflush((void *)&current_thread_info()->flags);
-			smp_mb(); /* quirk */
+			mb(); /* quirk */
 		}
 
 		__monitor((void *)&current_thread_info()->flags, 0, 0);