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authorMathieu Desnoyers <mathieu.desnoyers@efficios.com>2014-07-17 01:05:21 +0400
committerJohn Stultz <john.stultz@linaro.org>2014-07-24 02:01:54 +0400
commit9b0fd802e8c0545148324916055e7b40d97963fa (patch)
treeed3332e022543a236e187cd976a657433d35c786 /include/linux/seqlock.h
parent0ea5a520f73ca31abc4c10b6d5bc14a884a0641b (diff)
downloadlinux-9b0fd802e8c0545148324916055e7b40d97963fa.tar.xz
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@efficios.com> Cc: John Stultz <john.stultz@linaro.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: John Stultz <john.stultz@linaro.org>
Diffstat (limited to 'include/linux/seqlock.h')
-rw-r--r--include/linux/seqlock.h11
1 files changed, 11 insertions, 0 deletions
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index dcc64b9bfc41..cce6e7453592 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.
*/