[PATCH] x86_64: Fix race in cpu_local_* on preemptible kernels
When a process changes CPUs while doing the non atomic cpu_local_*
operations it might operate on the local_t of a different CPUs.
Fix that by disabling preemption.
Pointed out by Christopher Lameter
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/asm-x86_64/local.h b/include/asm-x86_64/local.h
index cd17945..e769e62 100644
--- a/include/asm-x86_64/local.h
+++ b/include/asm-x86_64/local.h
@@ -59,12 +59,26 @@
* This could be done better if we moved the per cpu data directly
* after GS.
*/
-#define cpu_local_read(v) local_read(&__get_cpu_var(v))
-#define cpu_local_set(v, i) local_set(&__get_cpu_var(v), (i))
-#define cpu_local_inc(v) local_inc(&__get_cpu_var(v))
-#define cpu_local_dec(v) local_dec(&__get_cpu_var(v))
-#define cpu_local_add(i, v) local_add((i), &__get_cpu_var(v))
-#define cpu_local_sub(i, v) local_sub((i), &__get_cpu_var(v))
+
+/* Need to disable preemption for the cpu local counters otherwise we could
+ still access a variable of a previous CPU in a non atomic way. */
+#define cpu_local_wrap_v(v) \
+ ({ local_t res__; \
+ preempt_disable(); \
+ res__ = (v); \
+ preempt_enable(); \
+ res__; })
+#define cpu_local_wrap(v) \
+ ({ preempt_disable(); \
+ v; \
+ preempt_enable(); }) \
+
+#define cpu_local_read(v) cpu_local_wrap_v(local_read(&__get_cpu_var(v)))
+#define cpu_local_set(v, i) cpu_local_wrap(local_set(&__get_cpu_var(v), (i)))
+#define cpu_local_inc(v) cpu_local_wrap(local_inc(&__get_cpu_var(v)))
+#define cpu_local_dec(v) cpu_local_wrap(local_dec(&__get_cpu_var(v)))
+#define cpu_local_add(i, v) cpu_local_wrap(local_add((i), &__get_cpu_var(v)))
+#define cpu_local_sub(i, v) cpu_local_wrap(local_sub((i), &__get_cpu_var(v)))
#define __cpu_local_inc(v) cpu_local_inc(v)
#define __cpu_local_dec(v) cpu_local_dec(v)