seqlock: seqcount_t latch: End read sections with read_seqcount_retry()

The seqcount_t latch reader example at the raw_write_seqcount_latch()
kernel-doc comment ends the latch read section with a manual smp memory
barrier and sequence counter comparison.

This is technically correct, but it is suboptimal: read_seqcount_retry()
already contains the same logic of an smp memory barrier and sequence
counter comparison.

End the latch read critical section example with read_seqcount_retry().

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/20200720155530.1173732-4-a.darwish@linutronix.de

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 6c4f68e..d724b5e 100644 (file)
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -363,8 +363,8 @@ static inline int raw_read_seqcount_latch(seqcount_t *s)
  *                     idx = seq & 0x01;
  *                     entry = data_query(latch->data[idx], ...);
  *
- *                     smp_rmb();
- *             } while (seq != latch->seq);
+ *             // read_seqcount_retry() includes needed smp_rmb()
+ *             } while (read_seqcount_retry(&latch->seq, seq));
  *
  *             return entry;
  *     }