Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

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"

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index ce54e98..0a06f91 100644 (file)
--- 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 1bb9548..436aa4e 100644 (file)
--- 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); \
 })