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

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Date:   Mon, 4 Feb 2019 17:38:48 +0000 (GMT)
From:   Thomas Gleixner <tglx@...utronix.de>
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>,
        jolsa@...hat.com, Namhyung Kim <namhyung@...nel.org>,
        luca abeni <luca.abeni@...tannapisa.it>,
        syzkaller <syzkaller@...glegroups.com>,
        Oleg Nesterov <oleg@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: perf_event_open+clone = unkillable process


On Mon, 4 Feb 2019, Dmitry Vyukov wrote:

> On Mon, Feb 4, 2019 at 10:27 AM Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > On Fri, 1 Feb 2019, 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.
> >
> > +Oleg, Eric
> >
> > That's odd. With some tracing I can see that SIGKILL is generated and
> > queued, but its not delivered by some weird reason. I'm traveling in the
> > next days, so I won't be able to do much about it. Will look later this
> > week.
> 
> Just a random though looking at the repro: can constant SIGBUS
> delivery starve delivery of all other signals (incl SIGKILL)?

Indeed. SIGBUS is 7, SIGKILL is 9 and next_signal() delivers the lowest
number first....

Thanks,

	tglx