From: "Ahmed S. Darwish" <a.darwish@linutronix.de>
Date: Thu, 27 Aug 2020 13:40:37 +0200
Subject: time/sched_clock: Use raw_read_seqcount_latch() during suspend
Patch-mainline: v5.10-rc1
Git-commit: 58faf20a086bd34f91983609e26eac3d5fe76be3
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 has one read memory
barrier less than the currently used raw_read_seqcount() API.

Use raw_read_seqcount_latch() for the suspend path.

Commit aadd6e5caaac ("time/sched_clock: Use raw_read_seqcount_latch()")
missed changing that instance of raw_read_seqcount().

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/20200715092345.GA231464@debian-buster-darwi.lab.linutronix.de
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
@@ -268,7 +268,7 @@ void __init generic_sched_clock_init(voi
  */
 static u64 notrace suspended_sched_clock_read(void)
 {
-	unsigned int seq = raw_read_seqcount(&cd.seq);
+	unsigned int seq = raw_read_seqcount_latch(&cd.seq);
 
 	return cd.read_data[seq & 1].epoch_cyc;
 }