[PATCH v5 4/5] x86: use mb() around clflush

[Michael S. Tsirkin]

commit f8e617f4582995f7c25ef25b4167213120ad122b ("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.

Cc: Mike Galbraith <bitbuc...@online.de>
Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
---
 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);
-- 
MST