diff options
authorLinus Torvalds <torvalds@linux-foundation.org>2014-11-23 11:33:49 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-11-23 11:33:49 -0800
commit9f2e0f6370b5f37cea3deee47299c8dfb0228eeb (patch)
parentd038a63ace6cf2ce3aeafa741b73d542ffb65163 (diff)
parent4aab3b5b3ccf94fc907e66233e6ca4d8675759a6 (diff)
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
1 files changed, 7 insertions, 1 deletions
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index d5c89e0dd0e6..51ce60c35f4c 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -133,7 +133,13 @@ static inline bool __ref_is_percpu(struct percpu_ref *ref,
/* paired with smp_store_release() in percpu_ref_reinit() */
- 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;