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| author | Mark Rutland <mark.rutland@arm.com> | 2017-10-23 23:07:23 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2017-10-25 11:01:04 +0200 |
| commit | 5cd38016d0c88e3f67528c1a7380a6d5c90859e9 (patch) | |
| tree | c6f5ff3ef0d78173e6408f8c4e0ee91c6eb8e112 | |
| parent | locking/atomics, workqueue: Convert ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE() (diff) | |
| download | linux-5cd38016d0c88e3f67528c1a7380a6d5c90859e9.tar.xz linux-5cd38016d0c88e3f67528c1a7380a6d5c90859e9.zip | |
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.rutland@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: davem@davemloft.net
Cc: linux-arch@vger.kernel.org
Cc: mpe@ellerman.id.au
Cc: shuah@kernel.org
Cc: snitzer@redhat.com
Cc: thor.thayer@linux.intel.com
Cc: tj@kernel.org
Cc: viro@zeniv.linux.org.uk
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1508792849-3115-13-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
| -rw-r--r-- | tools/testing/selftests/rcutorture/formal/srcu-cbmc/src/barriers.h | 5 |
1 files 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 6687acc08e6d..cc27b9ebcf20 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 |