On Sat, 28 Nov 2020 10:15:17 +0100 Andrea Righi <andrea.ri...@canonical.com> wrote:
> In the slow path of __rb_reserve_next() a nested event(s) can happen > between evaluating the timestamp delta of the current event and updating > write_stamp via local_cmpxchg(); in this case the delta is not valid > anymore and it should be set to 0 (same timestamp as the interrupting > event), since the event that we are currently processing is not the last > event in the buffer. > > Link: https://lwn.net/Articles/831207 And it looks like we have a WINNER! Thanks! It shows someone is paying attention. There's a few other patches I need to test, but I've queued this up for my next pull request. -- Steve > Fixes: a389d86f7fd0 ("ring-buffer: Have nested events still record running > time stamp") > Signed-off-by: Andrea Righi <andrea.ri...@canonical.com> > --- > kernel/trace/ring_buffer.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index dc83b3fa9fe7..5e30e0cdb6ce 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -3287,11 +3287,11 @@ __rb_reserve_next(struct ring_buffer_per_cpu > *cpu_buffer, > ts = rb_time_stamp(cpu_buffer->buffer); > barrier(); > /*E*/ if (write == (local_read(&tail_page->write) & > RB_WRITE_MASK) && > - info->after < ts) { > + info->after < ts && > + rb_time_cmpxchg(&cpu_buffer->write_stamp, > + info->after, info->ts)) { > /* 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->ts = ts; > } else { > /*
