Hello, Eric,
Does Johannes's recent change to lockless_dereference() help with
the sparse issue?
Thanx, Paul
----- Forwarded message from Ingo Molnar <[email protected]> -----
Date: Thu, 18 Aug 2016 22:34:21 +0200
From: Ingo Molnar <[email protected]>
To: Linus Torvalds <[email protected]>
Cc: [email protected], Peter Zijlstra <[email protected]>,
Thomas Gleixner <[email protected]>, Andrew Morton
<[email protected]>, "Paul E. McKenney" <[email protected]>
Subject: [GIT PULL] locking fixes
Linus,
Please pull the latest locking-urgent-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
locking-urgent-for-linus
# HEAD: 112dc0c8069e5554e0ad29c58228f1e6ca49e13d locking/barriers: Suppress
sparse warnings in lockless_dereference()
Two lockless_dereference() related fixes.
Thanks,
Ingo
------------------>
Johannes Berg (2):
Revert "drm/fb-helper: Reduce READ_ONCE(master) to lockless_dereference"
locking/barriers: Suppress sparse warnings in lockless_dereference()
drivers/gpu/drm/drm_fb_helper.c | 2 +-
include/linux/compiler.h | 6 +++---
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); \
})
----- End forwarded message -----
