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

[tip-bot for Michael S. Tsirkin]

Commit-ID:  ca59809ff6d572ae58fc6bedf7500f5a60fdbd64
Gitweb:     http://git.kernel.org/tip/ca59809ff6d572ae58fc6bedf7500f5a60fdbd64
Author:     Michael S. Tsirkin <m...@redhat.com>
AuthorDate: Thu, 28 Jan 2016 19:02:51 +0200
Committer:  Ingo Molnar <mi...@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 <m...@redhat.com>
Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Andy Lutomirski <l...@amacapital.net>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Brian Gerst <brge...@gmail.com>
Cc: Davidlohr Bueso <d...@stgolabs.net>
Cc: Davidlohr Bueso <dbu...@suse.de>
Cc: Denys Vlasenko <dvlas...@redhat.com>
Cc: H. Peter Anvin <h...@zytor.com>
Cc: Len Brown <len.br...@intel.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Mike Galbraith <bitbuc...@online.de>
Cc: Oleg Nesterov <o...@redhat.com>
Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: virtualization <virtualizat...@lists.linux-foundation.org>
Link: http://lkml.kernel.org/r/1453921746-16178-5-git-send-email-...@redhat.com
Signed-off-by: Ingo Molnar <mi...@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);