Merge branch 'for-3.18-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu
Pull percpu fix from Tejun Heo:
"This contains one patch to fix a race condition which can lead to
percpu_ref using a percpu pointer which is corrupted with a set DEAD
bit. The bug was introduced while separating out the ATOMIC mode flag
from the DEAD flag. The fix is pretty straight forward.
I just committed the patch to the percpu tree but am sending out the
pull request early as I'll be on vacation for a week. The patch
should be fairly safe and while the latency will be higher I'll be
checking emails"
* 'for-3.18-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu:
percpu-ref: fix DEAD flag contamination of percpu pointer
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index d5c89e0..51ce60c 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -133,7 +133,13 @@
/* paired with smp_store_release() in percpu_ref_reinit() */
smp_read_barrier_depends();
- if (unlikely(percpu_ptr & __PERCPU_REF_ATOMIC))
+ /*
+ * Theoretically, the following could test just ATOMIC; however,
+ * then we'd have to mask off DEAD separately as DEAD may be
+ * visible without ATOMIC if we race with percpu_ref_kill(). DEAD
+ * implies ATOMIC anyway. Test them together.
+ */
+ if (unlikely(percpu_ptr & __PERCPU_REF_ATOMIC_DEAD))
return false;
*percpu_countp = (unsigned long __percpu *)percpu_ptr;
