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| author |   Ahmed S. Darwish <a.darwish@linutronix.de> | 2020-07-20 17:55:12 +0200 |
|---|---|---|
| committer |   Peter Zijlstra <peterz@infradead.org> | 2020-07-29 16:14:24 +0200 |
| commit | 932e46365226324d2cf26d8bdec8b51ceb296948 (patch) | |
| tree | bef7aec2eec5bc5b2753ef09469faa88b32ddb52 /include/linux/seqlock.h | |
| parent | seqlock: Add kernel-doc for seqcount_t and seqlock_t APIs (diff) | |
| download | linux-dev-932e46365226324d2cf26d8bdec8b51ceb296948.tar.xz linux-dev-932e46365226324d2cf26d8bdec8b51ceb296948.zip | |
seqlock: Implement raw_seqcount_begin() in terms of raw_read_seqcount()
raw_seqcount_begin() has the same code as raw_read_seqcount(), with the
exception of masking the sequence counter's LSB before returning it to
the caller.
Note, raw_seqcount_begin() masks the counter's LSB before returning it
to the caller so that read_seqcount_retry() can fail if the counter is
odd -- without the overhead of an extra branching instruction.
Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200720155530.1173732-7-a.darwish@linutronix.de
Diffstat (limited to 'include/linux/seqlock.h')
| -rw-r--r-- | include/linux/seqlock.h | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index 85fb3ac93ffb..e885702d8b82 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -199,10 +199,11 @@ static inline unsigned raw_read_seqcount(const seqcount_t *s) */ static inline unsigned raw_seqcount_begin(const seqcount_t *s) { - unsigned ret = READ_ONCE(s->sequence); - smp_rmb(); - kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX); - return ret & ~1; + /* + * If the counter is odd, let read_seqcount_retry() fail + * by decrementing the counter. + */ + return raw_read_seqcount(s) & ~1; } /** |