Commit-ID: 564cbc87937d5de1b5b666b0ed68122d6c74fa07
Gitweb: https://git.kernel.org/tip/564cbc87937d5de1b5b666b0ed68122d6c74fa07
Author: Mark Rutland <mark.rutland@xxxxxxx>
AuthorDate: Mon, 23 Oct 2017 14:07:21 -0700
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 25 Oct 2017 11:01:02 +0200
locking/atomics, selftests/powerpc: Convert ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE()
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, and to align with
the preferred usage of {READ,WRITE}_ONCE(), this patch updates the DSCR
selftest code to use READ_ONCE() rather than ACCESS_ONCE(). There should
be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Acked-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: davem@xxxxxxxxxxxxx
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: snitzer@xxxxxxxxxx
Cc: thor.thayer@xxxxxxxxxxxxxxx
Cc: tj@xxxxxxxxxx
Cc: viro@xxxxxxxxxxxxxxxxxx
Cc: will.deacon@xxxxxxx
Link: http://lkml.kernel.org/r/1508792849-3115-11-git-send-email-paulmck@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
tools/testing/selftests/powerpc/dscr/dscr.h | 2 +-
tools/testing/selftests/powerpc/dscr/dscr_default_test.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/tools/testing/selftests/powerpc/dscr/dscr.h b/tools/testing/selftests/powerpc/dscr/dscr.h
index 18ea223b..cdb840b 100644
--- a/tools/testing/selftests/powerpc/dscr/dscr.h
+++ b/tools/testing/selftests/powerpc/dscr/dscr.h
@@ -39,7 +39,7 @@
#define rmb() asm volatile("lwsync":::"memory")
#define wmb() asm volatile("lwsync":::"memory")
-#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
+#define READ_ONCE(x) (*(volatile typeof(x) *)&(x))
/* Prilvilege state DSCR access */
inline unsigned long get_dscr(void)
diff --git a/tools/testing/selftests/powerpc/dscr/dscr_default_test.c b/tools/testing/selftests/powerpc/dscr/dscr_default_test.c
index df17c3b..9e1a37e 100644
--- a/tools/testing/selftests/powerpc/dscr/dscr_default_test.c
+++ b/tools/testing/selftests/powerpc/dscr/dscr_default_test.c
@@ -27,7 +27,7 @@ static void *do_test(void *in)
unsigned long d, cur_dscr, cur_dscr_usr;
unsigned long s1, s2;
- s1 = ACCESS_ONCE(sequence);
+ s1 = READ_ONCE(sequence);
if (s1 & 1)
continue;
rmb();
--
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