On Wed, Jul 15, 2020 at 10:05:07AM +0800, Leo Yan wrote: > From: Peter Zijlstra <pet...@infradead.org> > ... > > Provide struct clock_read_data and two (seqcount) helpers so that > architectures (arm64 in specific) can expose the numbers to userspace. > ... > > +struct clock_read_data *sched_clock_read_begin(unsigned int *seq) > +{ > + *seq = raw_read_seqcount(&cd.seq); > + return cd.read_data + (*seq & 1); > +} > + ...
Hmm, this seqcount_t is actually a latch seqcount. I know the original code also used raw_read_seqcount(), but while at it, let's use the proper read API for seqcount_t latchers: raw_read_seqcount_latch(). raw_read_seqcount_latch() has no read memory barrier though, and a suspicious claim that READ_ONCE() pairs with an smp_wmb() (??). But if its implementation is wrong, let's fix it there instead. Thanks, -- Ahmed S. Darwish Linutronix GmbH