Messages in this thread Patch in this message | | | From | Mark Rutland <> | Subject | [PATCH 13/13] rcutorture: formal: prepare for ACCESS_ONCE() removal | Date | Mon, 9 Oct 2017 19:28:50 +0100 |
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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 rcutorture formal tests to use an intermediate __ACCESS_ONCE() helper, which will avoid {READ,WRITE}_ONCE() being turned into tautological definitions. There should be no functional change as a result of this patch.
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Mark Rutland <mark.rutland@arm.com> --- tools/testing/selftests/rcutorture/formal/srcu-cbmc/src/barriers.h | 7 ++++--- 1 file changed, 4 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..ee4e4f8 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 +34,9 @@ #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 __ACCESS_ONCE(x) (*(volatile typeof(x) *) &(x)) +#define ACCESS_ONCE(x) __ACCESS_ONCE(x) +#define READ_ONCE(x) __ACCESS_ONCE(x) +#define WRITE_ONCE(x, val) (__ACCESS_ONCE(x) = (val)) #endif -- 1.9.1
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