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authorAhmed S. Darwish <a.darwish@linutronix.de>2020-07-20 18:55:12 +0300
committerPeter Zijlstra <peterz@infradead.org>2020-07-29 17:14:24 +0300
commit932e46365226324d2cf26d8bdec8b51ceb296948 (patch)
treebef7aec2eec5bc5b2753ef09469faa88b32ddb52 /include/linux/seqlock.h
parent89b88845e05752b3d684eaf147f457c8dfa99c5f (diff)
downloadlinux-932e46365226324d2cf26d8bdec8b51ceb296948.tar.xz
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.h9
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;
}
/**