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.
Link:
https://lkml.kernel.org/r/20200625085745.gd117...@hirez.programming.kicks-ass.net
Link:
https://lkml.kernel.org/r/20200715092345.ga231...@debian-buster-darwi.lab.linutronix.de
References: 1809bfa44e10 ("timers, sched/clock: Avoid deadlock during read from
NMI")
Signed-off-by: Ahmed S. Darwish <a.darw...@linutronix.de>
---
kernel/time/sched_clock.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index fa3f800d7d76..ea007928d681 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -100,7 +100,7 @@ unsigned long long notrace sched_clock(void)
struct clock_read_data *rd;
do {
- seq = raw_read_seqcount(&cd.seq);
+ seq = raw_read_seqcount_latch(&cd.seq);
rd = cd.read_data + (seq & 1);
cyc = (rd->read_sched_clock() - rd->epoch_cyc) &
--
2.20.1
