Commit-ID: 112dc0c8069e5554e0ad29c58228f1e6ca49e13d
Gitweb: http://git.kernel.org/tip/112dc0c8069e5554e0ad29c58228f1e6ca49e13d
Author: Johannes Berg <johannes.berg@xxxxxxxxx>
AuthorDate: Thu, 11 Aug 2016 11:50:22 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 18 Aug 2016 15:36:13 +0200
locking/barriers: Suppress sparse warnings in lockless_dereference()
After Peter's commit:
331b6d8c7afc ("locking/barriers: Validate lockless_dereference() is used on a pointer type")
... we get a lot of sparse warnings (one for every rcu_dereference, and more)
since the expression here is assigning to the wrong address space.
Instead of validating that 'p' is a pointer this way, instead make
it fail compilation when it's not by using sizeof(*(p)). This will
not cause any sparse warnings (tested, likely since the address
space is irrelevant for sizeof), and will fail compilation when
'p' isn't a pointer type.
Tested-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Fixes: 331b6d8c7afc ("locking/barriers: Validate lockless_dereference() is used on a pointer type")
Link: http://lkml.kernel.org/r/1470909022-687-2-git-send-email-johannes@xxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
include/linux/compiler.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 1bb9548..436aa4e 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); \
})
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