From: Oleg Nesterov <oleg@redhat.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Dmitry Vyukov <dvyukov@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
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>,
Ivan Delalande <colona@arista.com>
Subject: Re: [PATCH 1/2] signal: Always notice exiting tasks
Date: Tue, 12 Feb 2019 17:50:23 +0100 [thread overview]
Message-ID: <20190212165022.GA29263@redhat.com> (raw)
In-Reply-To: <871s4dctci.fsf@xmission.com>
On 02/12, Eric W. Biederman wrote:
>
> > Here I was trying for the simple minimal change and I hit this landmine.
> > Which leaves me with the question of what should be semantics of signal
> > handling after exit.
Yes, currently it is undefined. Even signal_pending() is random.
> > I think from dim memory of previous conversations the desired semantics
> > look like:
> > a) Ignore all signal state except for SIGKILL.
> > b) Letting SIGKILL wake up the process should be sufficient.
signal_wake_up(true) to make fatal_signal_pending() == T, I think.
> Oleg any ideas on how to make PTRACE_EVENT_EXIT reliably killable?
My answer is very simple: PTRACE_EVENT_EXIT must not stop if the tracee was
killed by the "real" SIGKILL (not by group_exit/etc), that is all. But this
is another user-visible change, it can equally confuse, say, strace (albeit
not too much iiuc).
But this needs another discussion.
> diff --git a/kernel/signal.c b/kernel/signal.c
> index 99fa8ff06fd9..a1f154dca73c 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2544,6 +2544,9 @@ bool get_signal(struct ksignal *ksig)
> }
>
> fatal:
> + /* No more signals can be pending past this point */
> + sigdelset(¤t->pending.signal, SIGKILL);
Well, this is very confusing. In fact, this is not really correct. Say, we should
not remove the pending SIGKILL if we are going to call do_coredump(). This is
possible if ptrace_signal() was called, or after is_current_pgrp_orphaned() returns
false.
> + clear_tsk_thread_flag(current, TIF_SIGPENDING);
I don't understand this change, it looks irrelevant. Possibly makes sense, but
this connects to "semantics of signal handling after exit".
OK, we need a minimal incremental fix for now. I'd suggest to replace
ksig->info.si_signo = signr = SIGKILL;
if (signal_group_exit(signal))
goto fatal;
added by this patch with
if (__fatal_signal_pending(current)) {
ksig->info.si_signo = signr = SIGKILL;
sigdelset(¤t->pending.signal, SIGKILL);
goto fatal;
}
__fatal_signal_pending() is cheaper and looks more understandable.
Oleg.
next prev parent reply other threads:[~2019-02-12 16:50 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-01 16:48 perf_event_open+clone = unkillable process 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
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 [this message]
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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