From: Keir Fraser <keir@xen.org>
Date: Sat, 5 Mar 2011 16:02:33 +0000 (+0000)
Subject: x86: Cache read of cpu_state in __cpu_die() for subsequent BUG_ON check.
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=e63aa7c25bcad93030b276c5fce6df175f4c4dd6;p=xen.git

x86: Cache read of cpu_state in __cpu_die() for subsequent BUG_ON check.

Otherwise compiler may re-read cpu_state for the BUG_ON and see a
modified value causing erroneous BUG.

Signed-off-by: Keir Fraser <keir@xen.org>
Signed-off-by: Liu, Jinsong <jinsong.liu@intel.com>
---

diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index 7c14f06286..39eb583e84 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -861,10 +861,11 @@ void __cpu_die(unsigned int cpu)
 {
     /* We don't do anything here: idle task is faking death itself. */
     unsigned int i = 0;
+    enum cpu_state seen_state;
 
-    while ( cpu_state != CPU_STATE_DEAD )
+    while ( (seen_state = cpu_state) != CPU_STATE_DEAD )
     {
-        BUG_ON(cpu_state != CPU_STATE_DYING);
+        BUG_ON(seen_state != CPU_STATE_DYING);
         mdelay(100);
         cpu_relax();
         process_pending_softirqs();