linux-kernel - Re: perf_event_open+clone = unkillable process

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Date:   Sun, 3 Feb 2019 16:21:13 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        luca abeni <luca.abeni@...tannapisa.it>,
        Thomas Gleixner <tglx@...utronix.de>,
        Oleg Nesterov <oleg@...hat.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: perf_event_open+clone = unkillable process

On Sat, Feb 02, 2019 at 07:30:45PM +0100, Jiri Olsa wrote:
> On Fri, Feb 01, 2019 at 06:06:03PM +0100, Dmitry Vyukov wrote:
> > On Fri, Feb 1, 2019 at 5:48 PM Dmitry Vyukov <dvyukov@...gle.com> wrote:
> > >
> > > Hello,
> > >
> > > The following program creates an unkillable process that eats CPU.
> > > /proc/pid/stack is empty, I am not sure what other info I can provide.
> > >
> > > Tested is on upstream commit 4aa9fc2a435abe95a1e8d7f8c7b3d6356514b37a.
> > > Config is attached.
> > 
> > Looking through other reproducers that create unkillable processes, I
> > think I found a much simpler reproducer (below). It's single threaded
> > and just setups SIGBUS handler and does timer_create+timer_settime to
> > send repeated SIGBUS. The resulting process can't be killed with
> > SIGKILL.
> > +Thomas for timers.
> 
> nice, I managed to kill it by strace ;-)
> 
> [jolsa@...va perf]$ strace  -p 10725
> strace: Process 10725 attached
> --- stopped by SIGBUS ---
> --- stopped by SIGBUS ---
> --- stopped by SIGBUS ---
> --- stopped by SIGBUS ---
> +++ killed by SIGINT +++

fyi I can no longer reproduce the kill via strace.. not sure
what was different

jirka