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authorLinus Torvalds <torvalds@linux-foundation.org>2016-08-18 13:45:48 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-08-18 13:45:48 -0700
commitbd3fd451ff3b205f0bde4d1bf7a310552c40d6e0 (patch)
treeaceca2fab7b29490405bfda1597e43573ffe99f6
parentf28535c100e3c3066ed3506d90948cf023dad21a (diff)
parent112dc0c8069e5554e0ad29c58228f1e6ca49e13d (diff)
Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking fixes from Ingo Molnar: "Two lockless_dereference() related fixes" * 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: locking/barriers: Suppress sparse warnings in lockless_dereference() Revert "drm/fb-helper: Reduce READ_ONCE(master) to lockless_dereference"
-rw-r--r--drivers/gpu/drm/drm_fb_helper.c2
-rw-r--r--include/linux/compiler.h6
2 files changed, 4 insertions, 4 deletions
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index ce54e985d91b..0a06f9120b5a 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -464,7 +464,7 @@ static bool drm_fb_helper_is_bound(struct drm_fb_helper *fb_helper)
/* Sometimes user space wants everything disabled, so don't steal the
* display if there's a master. */
- if (lockless_dereference(dev->master))
+ if (READ_ONCE(dev->master))
return false;
drm_for_each_crtc(crtc, dev) {
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 1bb954842725..436aa4e42221 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -527,13 +527,13 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
* object's lifetime is managed by something other than RCU. That
* "something other" might be reference counting or simple immortality.
*
- * The seemingly unused void * variable is to validate @p is indeed a pointer
- * type. All pointer types silently cast to void *.
+ * The seemingly unused size_t variable is to validate @p is indeed a pointer
+ * type by making sure it can be dereferenced.
*/
#define lockless_dereference(p) \
({ \
typeof(p) _________p1 = READ_ONCE(p); \
- __maybe_unused const void * const _________p2 = _________p1; \
+ size_t __maybe_unused __size_of_ptr = sizeof(*(p)); \
smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
(_________p1); \
})