linux-kernel - [PATCH] perf mmap: Convert ACCESS_ONCE() to READ

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Date:   Tue, 14 Nov 2017 10:31:38 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Mark Rutland <mark.rutland@....com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH] perf mmap: Convert ACCESS_ONCE() to READ_ONCE()

Recently there was a treewide conversion of ACCESS_ONCE() to
{READ,WRITE}_ONCE(), but a new use was introduced concurrently by
commit:

  1695849735752d2a ("perf mmap: Move perf_mmap and methods to separate mmap.[ch] files")

Let's convert this over to READ_ONCE() so that we can remove the
ACCESS_ONCE() definitions in subsequent patches.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
---
 tools/perf/util/mmap.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Hi,

Would it be possible for this to be taken as a fixup in an upcoming rc? That
way we should be able to remove the ACCESS_ONCE() definitions prior to v4.15.

Thanks,
Mark.

diff --git a/tools/perf/util/mmap.h b/tools/perf/util/mmap.h
index efd78b827b05..3a5cb5a6e94a 100644
--- a/tools/perf/util/mmap.h
+++ b/tools/perf/util/mmap.h
@@ -70,7 +70,7 @@ void perf_mmap__read_catchup(struct perf_mmap *md);
 static inline u64 perf_mmap__read_head(struct perf_mmap *mm)
 {
 	struct perf_event_mmap_page *pc = mm->base;
-	u64 head = ACCESS_ONCE(pc->data_head);
+	u64 head = READ_ONCE(pc->data_head);
 	rmb();
 	return head;
 }
-- 
2.11.0