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Diffstat (limited to 'arch/x86/xen/spinlock.c')
-rw-r--r--arch/x86/xen/spinlock.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 2f91e5651926..36a5141108df 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -326,8 +326,13 @@ static void xen_spin_unlock(struct raw_spinlock *lock)
smp_wmb(); /* make sure no writes get moved after unlock */
xl->lock = 0; /* release lock */
- /* make sure unlock happens before kick */
- barrier();
+ /*
+ * Make sure unlock happens before checking for waiting
+ * spinners. We need a strong barrier to enforce the
+ * write-read ordering to different memory locations, as the
+ * CPU makes no implied guarantees about their ordering.
+ */
+ mb();
if (unlikely(xl->spinners))
xen_spin_unlock_slow(xl);