From: "Ahmed S. Darwish" <a.darwish@linutronix.de>
Date: Mon, 20 Jul 2020 17:55:09 +0200
Subject: seqlock: seqcount_t latch: End read sections with
 read_seqcount_retry()
Patch-mainline: v5.9-rc1
Git-commit: d3b35b87f436c1b226a8061bee9c8875ba6658bd
References: bsc#1176564 bsc#1162702

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
Acked-by: Daniel Wagner <dwagner@suse.de>
---
 include/linux/seqlock.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -339,8 +339,8 @@ static inline int raw_read_seqcount_latc
  *			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;
  *	}