Commit-ID: 9b0fd802e8c0545148324916055e7b40d97963fa
Gitweb: http://git.kernel.org/tip/9b0fd802e8c0545148324916055e7b40d97963fa
Author: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
AuthorDate: Wed, 16 Jul 2014 21:05:21 +0000
Committer: John Stultz <john.stultz@xxxxxxxxxx>
CommitDate: Wed, 23 Jul 2014 15:01:54 -0700
seqcount: Add raw_write_seqcount_latch()
For NMI safe access to clock monotonic we use the seqcount LSB as
index of a timekeeper array. The update sequence looks like this:
smp_wmb(); <- prior stores to a[1]
seq++;
smp_wmb(); <- seq increment before update of a[0]
update(a[0]);
smp_wmb(); <- update of a[0]
seq++;
smp_wmb(); <- seq increment before update of a[1]
update(a[1]);
To avoid open coded barriers, provide a helper function.
[ tglx: Split out of a combo patch against the first implementation of
the NMI safe accessor ]
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
---
include/linux/seqlock.h | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index dcc64b9..cce6e74 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -236,6 +236,17 @@ static inline void raw_write_seqcount_end(seqcount_t *s)
}
/*
+ * raw_write_seqcount_latch - redirect readers to even/odd copy
+ * @s: pointer to seqcount_t
+ */
+static inline void raw_write_seqcount_latch(seqcount_t *s)
+{
+ smp_wmb(); /* prior stores before incrementing "sequence" */
+ s->sequence++;
+ smp_wmb(); /* increment "sequence" before following stores */
+}
+
+/*
* Sequence counter only version assumes that callers are using their
* own mutexing.
*/
--
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