Re: [PATCH v3] perf record: Use an eventfd to wakeup when done

Arnaldo Carvalho de Melo
2020-05-20T15:47:08Z

Em Wed, May 13, 2020 at 01:39:41PM +0200, Jiri Olsa escreveu:
> On Wed, May 13, 2020 at 12:20:23PM +1000, Anand K Mistry wrote:
> > The setting and checking of 'done' contains a rare race where the signal
> > handler setting 'done' is run after checking to break the loop, but
> > before waiting in evlist__poll(). In this case, the main loop won't wake
> > up until either another signal is sent, or the perf data fd causes a
> > wake up.
> >
> > The following simple script can trigger this condition (but you might
> > need to run it for several hours):
> > for ((i = 0; i >= 0; i++)) ; do
> > echo "Loop $i"
> > delay=$(echo "scale=4; 0.1 * $RANDOM/32768" | bc)
> > ./perf record -- sleep 30000000 >/dev/null&
> > pid=$!
> > sleep $delay
> > kill -TERM $pid
> > echo "PID $pid"
> > wait $pid
> > done
> >
> > At some point, the loop will stall. Adding logging, even though perf has
> > received the SIGTERM and set 'done = 1', perf will remain sleeping until
> > a second signal is sent.
> >
> > Signed-off-by: Anand K Mistry <amistry@google.com>
> >
> > ---
> >
> > Changes in v3:
> > - Move done_fd creation to below session initialisation
> > - Close done_fd on exit
> > - Log errno when write(done_fd) fails
>
> Acked-by: Jiri Olsa <jolsa@redhat.com>

I've made this dependent on HAVE_EVENTFD_SUPPORT, so that it continues
building on older systems,

- Arnaldo