From: Mathieu Desnoyers <[email protected]>
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 <[email protected]>
Cc: John Stultz <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Steven Rostedt <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
---
include/linux/seqlock.h | 11 +++++++++++
1 file changed, 11 insertions(+)
Index: tip/include/linux/seqlock.h
===================================================================
--- tip.orig/include/linux/seqlock.h
+++ tip/include/linux/seqlock.h
@@ -236,6 +236,17 @@ static inline void raw_write_seqcount_en
}
/*
+ * 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.
*/
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
