From: ebiederm@xmission.com (Eric W. Biederman)
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Dmitry Vyukov <dvyukov@google.com>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
jolsa@redhat.com, Namhyung Kim <namhyung@kernel.org>,
luca abeni <luca.abeni@santannapisa.it>,
syzkaller <syzkaller@googlegroups.com>,
Oleg Nesterov <oleg@redhat.com>
Subject: Re: perf_event_open+clone = unkillable process
Date: Mon, 04 Feb 2019 21:00:56 -0600 [thread overview]
Message-ID: <8736p37xcn.fsf@xmission.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1902041736240.3006@nanos.tec.linutronix.de> (Thomas Gleixner's message of "Mon, 4 Feb 2019 17:38:48 +0000 (GMT)")
Thomas Gleixner <tglx@linutronix.de> writes:
> On Mon, 4 Feb 2019, Dmitry Vyukov wrote:
>
>> On Mon, Feb 4, 2019 at 10:27 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>> >
>> > On Fri, 1 Feb 2019, Dmitry Vyukov wrote:
>> >
>> > > On Fri, Feb 1, 2019 at 5:48 PM Dmitry Vyukov <dvyukov@google.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....
We do have the special case in complete_signal that causes most of the
signal delivery work of SIGKILL to happen when SIGKILL is queued.
I need to look at your reproducer. It would require being a per-thread
signal to cause problems in next_signal.
It is definitely worth fixing if there is any way for userspace to block
SIGKILL.
Eric
next prev parent reply other threads:[~2019-02-05 3:01 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-01 16:48 Dmitry Vyukov
2019-02-01 17:06 ` Dmitry Vyukov
2019-02-02 18:30 ` Jiri Olsa
2019-02-03 15:21 ` Jiri Olsa
2019-02-04 9:27 ` Thomas Gleixner
2019-02-04 9:38 ` Dmitry Vyukov
2019-02-04 17:38 ` Thomas Gleixner
2019-02-05 3:00 ` Eric W. Biederman [this message]
2019-02-05 4:27 ` Eric W. Biederman
2019-02-05 6:07 ` Eric W. Biederman
2019-02-05 15:26 ` [RFC][PATCH] signal: Store pending signal exit in tsk.jobctl not in tsk.pending Eric W. Biederman
2019-02-06 12:09 ` Dmitry Vyukov
2019-02-06 21:47 ` Eric W. Biederman
2019-02-06 18:07 ` Oleg Nesterov
2019-02-06 22:25 ` Eric W. Biederman
2019-02-07 6:42 ` [PATCH 0/2]: Fixing unkillable processes caused by SIGHUP timers Eric W. Biederman
2019-02-07 6:43 ` [PATCH 1/2] signal: Always notice exiting tasks Eric W. Biederman
2019-02-11 14:13 ` Oleg Nesterov
2019-02-12 0:42 ` Eric W. Biederman
2019-02-12 8:18 ` Eric W. Biederman
2019-02-12 16:50 ` Oleg Nesterov
2019-02-13 3:58 ` Eric W. Biederman
2019-02-13 4:09 ` [PATCH] signal: Restore the stop PTRACE_EVENT_EXIT Eric W. Biederman
2019-02-13 13:55 ` Oleg Nesterov
2019-02-13 14:38 ` Oleg Nesterov
2019-02-13 14:58 ` Eric W. Biederman
2019-02-07 6:44 ` [PATCH 2/2] signal: Better detection of synchronous signals Eric W. Biederman
2019-02-11 15:18 ` Oleg Nesterov
2019-02-12 0:01 ` Eric W. Biederman
2019-02-12 17:21 ` Oleg Nesterov
2019-02-07 11:46 ` [PATCH 0/2]: Fixing unkillable processes caused by SIGHUP timers Dmitry Vyukov
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