Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1465366

[tip:locking/urgent] locking/barriers: Suppress sparse warnings in lockless_dereference()

Show all headers | View raw

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); \
 })

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 1/2] Revert "drm/fb-helper: Reduce READ_ONCE(master) to lockless_dereference" Johannes Berg <johannes@sipsolutions.net> - 2016-08-11 12:00 +0200
  [PATCH 2/2] locking/barriers: suppress sparse warnings in lockless_dereference() Johannes Berg <johannes@sipsolutions.net> - 2016-08-11 12:00 +0200
    [tip:locking/core] locking/barriers: Suppress sparse warnings in  lockless_dereference() tip-bot for Johannes Berg <tipbot@zytor.com> - 2016-08-18 13:10 +0200
    [tip:locking/urgent] locking/barriers: Suppress sparse warnings in  lockless_dereference() tip-bot for Johannes Berg <tipbot@zytor.com> - 2016-08-18 15:50 +0200
  Re: [PATCH 1/2] Revert "drm/fb-helper: Reduce READ_ONCE(master) to  lockless_dereference" Daniel Vetter <daniel@ffwll.ch> - 2016-08-11 12:40 +0200
    Re: [PATCH 1/2] Revert "drm/fb-helper: Reduce READ_ONCE(master) to  lockless_dereference" "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-08-12 00:30 +0200
      Re: [PATCH 1/2] Revert "drm/fb-helper: Reduce READ_ONCE(master) to  lockless_dereference" Johannes Berg <johannes@sipsolutions.net> - 2016-08-12 08:10 +0200
      Re: [PATCH 1/2] Revert "drm/fb-helper: Reduce READ_ONCE(master) to  lockless_dereference" Peter Zijlstra <peterz@infradead.org> - 2016-08-12 20:30 +0200
        Re: [PATCH 1/2] Revert "drm/fb-helper: Reduce READ_ONCE(master) to  lockless_dereference" "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-08-12 21:20 +0200
  [tip:locking/core] Revert "drm/fb-helper: Reduce READ_ONCE(master)  to lockless_dereference" tip-bot for Johannes Berg <tipbot@zytor.com> - 2016-08-18 13:10 +0200
  [tip:locking/urgent] Revert "drm/fb-helper: Reduce  READ_ONCE(master) to lockless_dereference" tip-bot for Johannes Berg <tipbot@zytor.com> - 2016-08-18 15:50 +0200

csiph-web