Commit 9b0fd802 authored by Mathieu Desnoyers's avatar Mathieu Desnoyers Committed by John Stultz

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: default avatarMathieu 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: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
parent 0ea5a520
......@@ -235,6 +235,17 @@ static inline void raw_write_seqcount_end(seqcount_t *s)
s->sequence++;
}
/*
* 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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