Commit-ID: 5cd38016d0c88e3f67528c1a7380a6d5c90859e9
Gitweb: https://git.kernel.org/tip/5cd38016d0c88e3f67528c1a7380a6d5c90859e9
Author: Mark Rutland <mark.rutl...@arm.com>
AuthorDate: Mon, 23 Oct 2017 14:07:23 -0700
Committer: Ingo Molnar <mi...@kernel.org>
CommitDate: Wed, 25 Oct 2017 11:01:04 +0200
locking/atomics, rcutorture/formal: Prepare for ACCESS_ONCE() removal
For several reasons, it is desirable to use {READ,WRITE}_ONCE() in
preference to ACCESS_ONCE(), and new code is expected to use one of the
former. So far, there's been no reason to change most existing uses of
ACCESS_ONCE(), as these aren't currently harmful.
However, for some features it is necessary to instrument reads and
writes separately, which is not possible with ACCESS_ONCE(). This
distinction is critical to correct operation.
The bulk of the kernel code can be transformed via Coccinelle to use
{READ,WRITE}_ONCE(), though this only modifies users of ACCESS_ONCE(),
and not the implementation itself. As such, it has the potential to
break homebrew ACCESS_ONCE() macros seen in some user code in the kernel
tree (e.g. the virtio code, as fixed in commit ea9156fb3b71d9f7).
To avoid fragility if/when that transformation occurs, this patch
reworks the definitions of {READ,WRITE}_ONCE() in the rcutorture formal
tests, and removes the unused ACCESS_ONCE() helper. There should be no
functional change as a result of this patch.
Signed-off-by: Mark Rutland <mark.rutl...@arm.com>
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: da...@davemloft.net
Cc: linux-a...@vger.kernel.org
Cc: m...@ellerman.id.au
Cc: sh...@kernel.org
Cc: snit...@redhat.com
Cc: thor.tha...@linux.intel.com
Cc: t...@kernel.org
Cc: v...@zeniv.linux.org.uk
Cc: will.dea...@arm.com
Link:
http://lkml.kernel.org/r/1508792849-3115-13-git-send-email-paul...@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
tools/testing/selftests/rcutorture/formal/srcu-cbmc/src/barriers.h | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/tools/testing/selftests/rcutorture/formal/srcu-cbmc/src/barriers.h
b/tools/testing/selftests/rcutorture/formal/srcu-cbmc/src/barriers.h
index 6687acc..cc27b9e 100644
--- a/tools/testing/selftests/rcutorture/formal/srcu-cbmc/src/barriers.h
+++ b/tools/testing/selftests/rcutorture/formal/srcu-cbmc/src/barriers.h
@@ -34,8 +34,7 @@
#define rs_smp_mb() do {} while (0)
#endif
-#define ACCESS_ONCE(x) (*(volatile typeof(x) *) &(x))
-#define READ_ONCE(x) ACCESS_ONCE(x)
-#define WRITE_ONCE(x, val) (ACCESS_ONCE(x) = (val))
+#define READ_ONCE(x) (*(volatile typeof(x) *) &(x))
+#define WRITE_ONCE(x) ((*(volatile typeof(x) *) &(x)) = (val))
#endif
