On Thu, Oct 11, 2018 at 8:02 AM Eric Dumazet <[email protected]> wrote: > > On Thu, Oct 11, 2018 at 3:45 AM Peter Zijlstra <[email protected]> wrote: > > > > Eric reported that a sequence count loop using this_cpu_read() got > > optimized out. This is wrong, this_cpu_read() must imply READ_ONCE() > > because the interface is IRQ-safe, therefore an interrupt can have > > changed the per-cpu value. > > > > Fixes: 59eaef78bfea ("x86/tsc: Remodel cyc2ns to use seqcount_latch()") > > Reported-by: Eric Dumazet <[email protected]> > > Signed-off-by: Peter Zijlstra (Intel) <[email protected]> > > > Acked-by: Eric Dumazet <[email protected]>
Actually the Fixes: tag seems funky. Bug was not added by 59eaef78bfea Your patch probably needs to be backported to older versions of linux, just to be safe, since we might have other places where authors relied on this_cpu_read() semantic (different than this_cpu_read_stable())
