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authorJohannes Berg <johannes.berg@intel.com>2016-08-26 09:16:00 +0300
committerIngo Molnar <mingo@kernel.org>2016-09-05 12:50:42 +0300
commitd7127b5e5fa0551be21b86640f1648b224e36d43 (patch)
treedd35da3a05da721d36c353ddea11555d4eb14362 /include/linux/compiler.h
parentc6935931c1894ff857616ff8549b61236a19148f (diff)
downloadlinux-d7127b5e5fa0551be21b86640f1648b224e36d43.tar.xz
locking/barriers: Don't use sizeof(void) in lockless_dereference()
My previous commit: 112dc0c8069e ("locking/barriers: Suppress sparse warnings in lockless_dereference()") caused sparse to complain that (in radix-tree.h) we use sizeof(void) since that rcu_dereference()s a void *. Really, all we need is to have the expression *p in here somewhere to make sure p is a pointer type, and sizeof(*p) was the thing that came to my mind first to make sure that's done without really doing anything at runtime. Another thing I had considered was using typeof(*p), but obviously we can't just declare a typeof(*p) variable either, since that may end up being void. Declaring a variable as typeof(*p)* gets around that, and still checks that typeof(*p) is valid, so do that. This type construction can't be done for _________p1 because that will actually be used and causes sparse address space warnings, so keep a separate unused variable for it. Reported-by: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Johannes Berg <johannes.berg@intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E . McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: kbuild-all@01.org Fixes: 112dc0c8069e ("locking/barriers: Suppress sparse warnings in lockless_dereference()") Link: http://lkml.kernel.org/r/1472192160-4049-1-git-send-email-johannes@sipsolutions.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/compiler.h')
-rw-r--r--include/linux/compiler.h7
1 files changed, 4 insertions, 3 deletions
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 436aa4e42221..668569844d37 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -527,13 +527,14 @@ 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 size_t variable is to validate @p is indeed a pointer
- * type by making sure it can be dereferenced.
+ * The seemingly unused variable ___typecheck_p validates that @p is
+ * indeed a pointer type by using a pointer to typeof(*p) as the type.
+ * Taking a pointer to typeof(*p) again is needed in case p is void *.
*/
#define lockless_dereference(p) \
({ \
typeof(p) _________p1 = READ_ONCE(p); \
- size_t __maybe_unused __size_of_ptr = sizeof(*(p)); \
+ typeof(*(p)) *___typecheck_p __maybe_unused; \
smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
(_________p1); \
})