[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>

1 files changed, 20 insertions, 6 deletions

diff --git a/include/asm-i386/local.h b/include/asm-i386/local.h
index e67fa08260fe..3b4998c51d08 100644
--- a/include/asm-i386/local.h
+++ b/include/asm-i386/local.h
@@ -55,12 +55,26 @@ static __inline__ void local_sub(long i, local_t *v)
  * much more efficient than these naive implementations.  Note they take
  * a variable, not an address.
  */
-#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)