1 files changed, 18 insertions, 10 deletions

diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 5601506f2dd..36a5141108d 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -187,7 +187,6 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock, bool irq_enabl
         struct xen_spinlock *prev;
         int irq = __get_cpu_var(lock_kicker_irq);
         int ret;
-        unsigned long flags;
         u64 start;
 
         /* If kicker interrupts not initialized yet, just spin */
@@ -199,16 +198,12 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock, bool irq_enabl
         /* announce we're spinning */
         prev = spinning_lock(xl);
 
-        flags = __raw_local_save_flags();
-        if (irq_enable) {
-                ADD_STATS(taken_slow_irqenable, 1);
-                raw_local_irq_enable();
-        }
-
         ADD_STATS(taken_slow, 1);
         ADD_STATS(taken_slow_nested, prev != NULL);
 
         do {
+                unsigned long flags;
+
                 /* clear pending */
                 xen_clear_irq_pending(irq);
 
@@ -228,6 +223,12 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock, bool irq_enabl
                         goto out;
                 }
 
+                flags = __raw_local_save_flags();
+                if (irq_enable) {
+                        ADD_STATS(taken_slow_irqenable, 1);
+                        raw_local_irq_enable();
+                }
+
                 /*
                  * Block until irq becomes pending.  If we're
                  * interrupted at this point (after the trylock but
@@ -238,13 +239,15 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock, bool irq_enabl
                  * pending.
                  */
                 xen_poll_irq(irq);
+
+                raw_local_irq_restore(flags);
+
                 ADD_STATS(taken_slow_spurious, !xen_test_irq_pending(irq));
         } while (!xen_test_irq_pending(irq)); /* check for spurious wakeups */
 
         kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));
 
 out:
-        raw_local_irq_restore(flags);
         unspinning_lock(xl, prev);
         spin_time_accum_blocked(start);
 
@@ -323,8 +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);