On Thu, 26 Nov 2020 13:26:13 -0500 Steven Rostedt <rost...@goodmis.org> wrote:
> On Thu, 26 Nov 2020 06:52:45 +0100 > Greg KH <gre...@linuxfoundation.org> wrote: > > > On Tue, Nov 24, 2020 at 10:39:17PM +0000, J. Avila wrote: > > > Hello, > > > > > > In the ftrace logs we've collected internally, we have found that there > > > are > > > situations where time seems to go backwards; this breaks userspace tools > > > which > > > expect time to always go forward in these logs. For example, in this > > > snippet > > > from a db845c running a 5.10-rc4 kernel[1] (thanks for getting us the > > > trace, > > > John!), we see: > > > > Does the patch at: > > https://lore.kernel.org/r/20201125225654.1618966-1-minc...@kernel.org > > > > resolve this issue for you? > > > > I think I found the bug. Can you apply this patch and let me know if it > fixes the issue for you? > > -- Steve > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index dc83b3fa9fe7..bccaf88d3706 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -3291,7 +3291,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu > *cpu_buffer, > /* Nothing came after this event between C and E */ > info->delta = ts - info->after; > (void)rb_time_cmpxchg(&cpu_buffer->write_stamp, > - info->after, info->ts); > + info->after, ts); > info->ts = ts; > } else { > /* > Can I get a Tested-by from someone on the Google team, so that I can send this upstream? It already passed all my internal testing, but I want to make sure this is the fix for the issue I reference in the change log. -- Steve
