From: "Ahmed S. Darwish" <a.darwish@linutronix.de>
Date: Thu, 16 Jul 2020 13:11:25 +0800
Subject: time/sched_clock: Use raw_read_seqcount_latch()
Patch-mainline: v5.9-rc1
Git-commit: aadd6e5caaacd6feca9691ba30536e7de5a7d152
References: bsc#1176564 bsc#1162702

sched_clock uses seqcount_t latching to switch between two storage
places protected by the sequence counter. This allows it to have
interruptible, NMI-safe, seqcount_t write side critical sections.

Since 7fc26327b756 ("seqlock: Introduce raw_read_seqcount_latch()"),
raw_read_seqcount_latch() became the standardized way for seqcount_t
latch read paths. Due to the dependent load, it also has one read
memory barrier less than the currently used raw_read_seqcount() API.

Use raw_read_seqcount_latch() for the seqcount_t latch read path.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Link: https://lkml.kernel.org/r/20200625085745.GD117543@hirez.programming.kicks-ass.net
Link: https://lkml.kernel.org/r/20200715092345.GA231464@debian-buster-darwi.lab.linutronix.de
Link: https://lore.kernel.org/r/20200716051130.4359-3-leo.yan@linaro.org
Signed-off-by: Will Deacon <will@kernel.org>
[dwagner: due to missing clock expore API changes context updated]
Acked-by: Daniel Wagner <dwagner@suse.de>
---
 kernel/time/sched_clock.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -68,7 +68,7 @@ static inline u64 notrace cyc_to_ns(u64
 
 struct clock_read_data *sched_clock_read_begin(unsigned int *seq)
 {
-	*seq = raw_read_seqcount(&cd.seq);
+	*seq = raw_read_seqcount_latch(&cd.seq);
 	return cd.read_data + (*seq & 1);
 }