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 <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Len Brown <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: virtualization <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 9f7c21c22477e59462d72e930d79a4c2a238a051..9decee2bfdbeedb795d3e1f423e606cdec5e49e0 100644 (file)
--- 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);