From: Mathieu Desnoyers 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 Cc: John Stultz Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Steven Rostedt Signed-off-by: Thomas Gleixner --- 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 majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/