Hello Steven, Thank you once again for all of your support. We saw that you also recently merged a change[1] which adds some validation for the timestamps in ring_buffer.c. Would you have any recommendations on how to add a more lightweight check for time going "backwards" in the timestamps? The idea is that we could use this quick test to detect the problem, then run a build with your config to dig deeper.
Thanks, Avila [1] https://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git/commit/?h=for-next On Mon, Nov 30, 2020 at 10:13 AM William Mcvicker <willmcvic...@google.com> wrote: > > On Mon, Nov 30, 2020 at 09:48:46AM -0500, Steven Rostedt wrote: > > 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 > > > > -- > > To unsubscribe from this group and stop receiving emails from it, send an > > email to kernel-team+unsubscr...@android.com. > > > Hi Steve, > > Thanks for the quick turnaround! Daniel and I have both tested your patch and > verified it's working on our end. Feel free to include: > > Tested-by: Daniel Mentz <danielme...@google.com> > Tested-by: Will McVicker <willmcvic...@google.com> > > --Will
