linux-kernel - Re: perf segfault in in ordered_events_

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Date:   Wed, 16 Jan 2019 23:33:55 -0800
From:   Song Liu <liu.song.a23@...il.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     open list <linux-kernel@...r.kernel.org>,
        Jiri Olsa <jolsa@...nel.org>, acme@...nel.org
Subject: Re: perf segfault in in ordered_events__free()

On Wed, Jan 16, 2019 at 1:53 PM Song Liu <liu.song.a23@...il.com> wrote:
>
> Thanks Jiri!
>
> On Wed, Jan 16, 2019 at 1:34 PM Jiri Olsa <jolsa@...hat.com> wrote:
> >
> > On Wed, Jan 16, 2019 at 10:57:49AM -0800, Song Liu wrote:
> > > Hi,
> > >
> > > We are debugging a segfault of perf in ordered_events__free().
> >
> > hi,
> > any backtrace or info on how to reproduce it?
>
> Here is the backtrace:
>
> #0  0x0000000000500055 in ordered_events(float, long double,...)(...) ()
> #1  0x0000000000500196 in ordered_events.reinit ()
> #2  0x00000000004fe413 in perf_session.process_events ()
> #3  0x0000000000440431 in cmd_record ()
> #4  0x00000000004a439f in run_builtin ()
> #5  0x000000000042b3e5 in main ()"
>
> >
> > > Disassemble shows the segfault was caused by oe->buff == NULL
> > > in the following line:
> > >
> > >         /*
> > >          * Current buffer might not have all the events allocated
> > >          * yet, we need to free only allocated ones ...
> > >          */
> > >         list_del(&oe->buffer->list);
> > >
> > > After poking around the code, I suspect it is caused by the following
> > > condition in alloc_event():
> > >
> > >         } else if (oe->buffer) {
> > >                 new = &oe->buffer->event[oe->buffer_idx];
> > >                 if (++oe->buffer_idx == MAX_SAMPLE_BUFFER)
> > >                         oe->buffer = NULL;
> >
> >
> > argh.. yea, we need to check oe->buffer in ordered_events__free
> >
> > would attached change fix it for you?
>
> Let me try roll a fixed version to confirm.

Yes, the patch fixes this segfault. Please CC me on the official patch to
back port the official version.

Thanks,
Song