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author | Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | 2014-07-16 21:05:21 +0000 |
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committer | John Stultz <john.stultz@linaro.org> | 2014-07-23 15:01:54 -0700 |
commit | 9b0fd802e8c0545148324916055e7b40d97963fa (patch) | |
tree | ed3332e022543a236e187cd976a657433d35c786 /include/linux/seqlock.h | |
parent | 0ea5a520f73ca31abc4c10b6d5bc14a884a0641b (diff) | |
download | linux-9b0fd802e8c0545148324916055e7b40d97963fa.tar.gz linux-9b0fd802e8c0545148324916055e7b40d97963fa.tar.bz2 linux-9b0fd802e8c0545148324916055e7b40d97963fa.zip |
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.h | 11 |
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. */ |