1 files changed, 18 insertions, 11 deletions

diff --git a/include/linux/spinlock_up.h b/include/linux/spinlock_up.h
index a26e2fb604e6..e2369c167dbd 100644
--- a/include/linux/spinlock_up.h
+++ b/include/linux/spinlock_up.h
@@ -16,7 +16,10 @@
  * In the debug case, 1 means unlocked, 0 means locked. (the values
  * are inverted, to catch initialization bugs)
  *
- * No atomicity anywhere, we are on UP.
+ * No atomicity anywhere, we are on UP. However, we still need
+ * the compiler barriers, because we do not want the compiler to
+ * move potentially faulting instructions (notably user accesses)
+ * into the locked sequence, resulting in non-atomic execution.
  */
 
 #ifdef CONFIG_DEBUG_SPINLOCK
@@ -25,6 +28,7 @@
 static inline void arch_spin_lock(arch_spinlock_t *lock)
 {
         lock->slock = 0;
+        barrier();
 }
 
 static inline void
@@ -32,6 +36,7 @@ arch_spin_lock_flags(arch_spinlock_t *lock, unsigned long flags)
 {
         local_irq_save(flags);
         lock->slock = 0;
+        barrier();
 }
 
 static inline int arch_spin_trylock(arch_spinlock_t *lock)
@@ -39,32 +44,34 @@ static inline int arch_spin_trylock(arch_spinlock_t *lock)
         char oldval = lock->slock;
 
         lock->slock = 0;
+        barrier();
 
         return oldval > 0;
 }
 
 static inline void arch_spin_unlock(arch_spinlock_t *lock)
 {
+        barrier();
         lock->slock = 1;
 }
 
 /*
  * Read-write spinlocks. No debug version.
  */
-#define arch_read_lock(lock)            do { (void)(lock); } while (0)
-#define arch_write_lock(lock)           do { (void)(lock); } while (0)
-#define arch_read_trylock(lock) ({ (void)(lock); 1; })
-#define arch_write_trylock(lock)        ({ (void)(lock); 1; })
-#define arch_read_unlock(lock)          do { (void)(lock); } while (0)
-#define arch_write_unlock(lock) do { (void)(lock); } while (0)
+#define arch_read_lock(lock)            do { barrier(); (void)(lock); } while (0)
+#define arch_write_lock(lock)           do { barrier(); (void)(lock); } while (0)
+#define arch_read_trylock(lock) ({ barrier(); (void)(lock); 1; })
+#define arch_write_trylock(lock)        ({ barrier(); (void)(lock); 1; })
+#define arch_read_unlock(lock)          do { barrier(); (void)(lock); } while (0)
+#define arch_write_unlock(lock) do { barrier(); (void)(lock); } while (0)
 
 #else /* DEBUG_SPINLOCK */
 #define arch_spin_is_locked(lock)       ((void)(lock), 0)
 /* for sched.c and kernel_lock.c: */
-# define arch_spin_lock(lock)           do { (void)(lock); } while (0)
-# define arch_spin_lock_flags(lock, flags)      do { (void)(lock); } while (0)
-# define arch_spin_unlock(lock) do { (void)(lock); } while (0)
-# define arch_spin_trylock(lock)        ({ (void)(lock); 1; })
+# define arch_spin_lock(lock)           do { barrier(); (void)(lock); } while (0)
+# define arch_spin_lock_flags(lock, flags)      do { barrier(); (void)(lock); } while (0)
+# define arch_spin_unlock(lock) do { barrier(); (void)(lock); } while (0)
+# define arch_spin_trylock(lock)        ({ barrier(); (void)(lock); 1; })
 #endif /* DEBUG_SPINLOCK */
 
 #define arch_spin_is_contended(lock)    (((void)(lock), 0))