[Intel-gfx] [PATCH igt] lib: Always enable ftrace-dump-on-oops

[Chris Wilson]

Quoting Petri Latvala (2017-11-08 12:32:09)
> On Wed, Nov 08, 2017 at 12:18:40PM +0000, Chris Wilson wrote:
> > Some debugging information is too voluminous to enable by default, yet
> > may be invaluable when it comes to post-mortem debugging. trace_printk()
> > provides the facility for the trace ringbuffer to be dumped on oops,
> > this way we can cheaply spam the debug log and only present it in case
> > of emergency.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > ---
> >  lib/igt_core.c | 23 +++++++++++++++++++++++
> >  1 file changed, 23 insertions(+)
> > 
> > diff --git a/lib/igt_core.c b/lib/igt_core.c
> > index 538a4472..ba4622d6 100644
> > --- a/lib/igt_core.c
> > +++ b/lib/igt_core.c
> > @@ -561,6 +561,28 @@ static void low_mem_killer_disable(bool disable)
> >       chmod(adj_fname, buf.st_mode);
> >  }
> >  
> > +/*
> > + * If the test takes out the machine, in addition to the usual dmesg
> > + * spam, the kernel may also emit a "death rattle" -- extra debug
> > + * information that is overkill for normal successful tests, but
> > + * vital for post-mortem analysis.
> > + */
> > +static void ftrace_dump_on_oops(bool enable)
> > +{
> > +     int fd;
> > +
> > +     fd = open("/proc/sys/kernel/ftrace_dump_on_oops", O_WRONLY);
> > +     if (fd < 0)
> > +             return;
> > +
> > +     /*
> > +      * If we fail, we do not get the death rattle we wish, but we
> > +      * still want to run the tests anyway.
> > +      */
> > +     igt_ignore_warn(write(fd, enable ? "1\n" : "0\n", 2));
> > +     close(fd);
> > +}
> > +
> >  bool igt_exit_called;
> >  static void common_exit_handler(int sig)
> >  {
> > @@ -858,6 +880,7 @@ out:
> >               sync();
> >               oom_adjust_for_doom();
> >               low_mem_killer_disable(true);
> > +             ftrace_dump_on_oops(true);
> 
> 
> Is there a call to disable it too? Or rather, restore the value that
> was there before executing a test.

No, because I didn't care. If the machine dies after the process
excited, that death rattle may still be important.
-Chris