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