On Wed, Jul 15, 2020 at 11:29:26PM +0800, Leo Yan wrote:
> Hi Peter, Ahmed,
>
> On Wed, Jul 15, 2020 at 01:59:01PM +0200, Ahmed S. Darwish wrote:
> > 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);
>
> Understand this is doing the same thing with __ktime_get_fast_ns() and
> I saw Peter acked to make change for this.
>
> Just want to confirm, since this patch introduces conflict with the
> patch set "arm64: perf: Proper cap_user_time* support" [1], I should
> rebase the patch set on top of this patch, right?
Or rebase this patch on top of yours and include it, either way.
