x86, hotplug: Move WBINVD back outside the play_dead loop

On processors with hyperthreading, when only one thread is offlined
the other thread can cause a spurious wakeup on the idled thread.  We
do not want to re-WBINVD when that happens.

Ideally, we should simply skip WBINVD unless we're the last thread on
a particular core to shut down, but there might be similar issues
elsewhere in the system.

Thus, revert to previous behavior of only WBINVD outside the loop.
Partly as a result, remove the mb()'s around it: they are not
necessary since wbinvd() is a serializing instruction, but they were
intended to make sure the compiler didn't do any funny loop
optimizations.

Reported-by: Asit Mallick <asit.k.mallick@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Arjan van de Ven <arjan@linux.kernel.org>
Cc: Len Brown <lenb@kernel.org>
Cc: Venkatesh Pallipadi <venki@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.hl>
LKML-Reference: <tip-ea53069231f9317062910d6e772cca4ce93de8c8@git.kernel.org>

1 files changed, 5 insertions, 6 deletions

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 07bf4233441d..55c80ffb8719 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1422,9 +1422,9 @@ static inline void mwait_play_dead(void)
                         (highest_subcstate - 1);
         }
 
+        wbinvd();
+
         while (1) {
-                mb();
-                wbinvd();
                 __monitor(&current_thread_info()->flags, 0, 0);
                 mb();
                 __mwait(eax, 0);
@@ -1433,11 +1433,10 @@ static inline void mwait_play_dead(void)
 
 static inline void hlt_play_dead(void)
 {
+        if (current_cpu_data.x86 >= 4)
+                wbinvd();
+
         while (1) {
-                mb();
-                if (current_cpu_data.x86 >= 4)
-                        wbinvd();
-                mb();
                 native_halt();
         }
 }