linux-kernel - Re: perf segfault in in ordered_events_

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Date:   Thu, 17 Jan 2019 10:18:23 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Song Liu <liu.song.a23@...il.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 11:33:55PM -0800, Song Liu wrote:
> 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 for testing, will post it today

jirka