Messages in this thread Patch in this message | | | Date | Thu, 18 Aug 2016 06:40:57 -0700 | From | tip-bot for Johannes Berg <> | Subject | [tip:locking/urgent] locking/barriers: Suppress sparse warnings in lockless_dereference() |
| |
Commit-ID: 112dc0c8069e5554e0ad29c58228f1e6ca49e13d Gitweb: http://git.kernel.org/tip/112dc0c8069e5554e0ad29c58228f1e6ca49e13d Author: Johannes Berg <johannes.berg@intel.com> AuthorDate: Thu, 11 Aug 2016 11:50:22 +0200 Committer: Ingo Molnar <mingo@kernel.org> 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@linux.vnet.ibm.com> Signed-off-by: Johannes Berg <johannes.berg@intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Chris Wilson <chris@chris-wilson.co.uk> Cc: Daniel Vetter <daniel.vetter@intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> 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@sipsolutions.net Signed-off-by: Ingo Molnar <mingo@kernel.org> --- 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); \ })
| |