From: Tycho Andersen <tycho@tycho.pizza>
To: Oleg Nesterov <oleg@redhat.com>
Cc: "Serge E. Hallyn" <serge@hallyn.com>,
"Eric W . Biederman" <ebiederm@xmission.com>,
Miklos Szeredi <miklos@szeredi.hu>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sched: __fatal_signal_pending() should also check PF_EXITING
Date: Wed, 27 Jul 2022 13:40:57 -0600 [thread overview]
Message-ID: <YuGUyayVWDB7R89i@tycho.pizza> (raw)
In-Reply-To: <20220727191949.GD18822@redhat.com>
On Wed, Jul 27, 2022 at 09:19:50PM +0200, Oleg Nesterov wrote:
> On 07/27, Tycho Andersen wrote:
> >
> > On Wed, Jul 27, 2022 at 07:55:39PM +0200, Oleg Nesterov wrote:
> > > On 07/27, Tycho Andersen wrote:
> > > >
> > > > Hi all,
> > > >
> > > > On Wed, Jul 20, 2022 at 08:54:59PM -0500, Serge E. Hallyn wrote:
> > > > > Oh - I didn't either - checking the sigkill in shared signals *seems*
> > > > > legit if they can be put there - but since you posted the new patch I
> > > > > assumed his reasoning was clear to you. I know Eric's busy, cc:ing Oleg
> > > > > for his interpretation too.
> > > >
> > > > Any thoughts on this?
> > >
> > > Cough... I don't know what can I say except I personally dislike this
> > > patch no matter what ;)
> > >
> > > And I do not understand how can this patch help. OK, a single-threaded
> > > PF_EXITING task sleeps in TASK_KILLABLE. send_signal_locked() won't
> > > wake it up anyway?
> > >
> > > I must have missed something.
> >
> > What do you think of the patch in
> > https://lore.kernel.org/all/YsyHMVLuT5U6mm+I@netflix/ ? Hopefully that
> > has an explanation that makes more sense.
>
> Sorry, I still do not follow. Again, I can easily miss something. But how
> can ANY change in __fatal_signal_pending() ensure that SIGKILL will wakeup
> a PF_EXITING task which already sleeps in TASK_KILLABLE state? or even set
> TIF_SIGPENDING as the changelog states?
__fatal_signal_pending() just checks the non-shared set:
sigismember(&p->pending.signal, SIGKILL)
When init in a pid namespace dies, it calls zap_pid_ns_processes(),
which does:
group_send_sig_info(SIGKILL, SEND_SIG_PRIV, task, PIDTYPE_MAX);
that eventually gets to __send_signal_locked() which does:
pending = (type != PIDTYPE_PID) ? &t->signal->shared_pending : &t->pending;
i.e. it decides to put the signal in the shared set, instead of the individual
set. If we change __fatal_signal_pending() to look in the shared set too, it
will exit all the wait code in this case.
Maybe it should be fixed somehow by complete_signal(), but that doesn't work if
the thread is already PF_EXITING, because wants_signal() will cause it to
ignore the task, so it remains stuck forever.
Does that make sense? Maybe it's me who is missing something. I have a
reproducer here:
https://github.com/tych0/kernel-utils/tree/master/fuse2
Tycho
next prev parent reply other threads:[~2022-07-27 19:41 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-23 17:21 strange interaction between fuse + pidns Tycho Andersen
2022-06-23 21:55 ` Vivek Goyal
2022-06-23 23:41 ` Tycho Andersen
2022-06-24 17:36 ` Vivek Goyal
2022-07-11 10:35 ` Miklos Szeredi
2022-07-11 13:59 ` Miklos Szeredi
2022-07-11 20:25 ` Tycho Andersen
2022-07-11 21:37 ` Eric W. Biederman
2022-07-11 22:53 ` Tycho Andersen
2022-07-11 23:06 ` Eric W. Biederman
2022-07-12 13:43 ` Tycho Andersen
2022-07-12 14:34 ` Eric W. Biederman
2022-07-12 15:14 ` Tycho Andersen
2022-07-13 17:53 ` [PATCH] sched: __fatal_signal_pending() should also check PF_EXITING Tycho Andersen
2022-07-20 15:03 ` Serge E. Hallyn
2022-07-20 20:58 ` Tycho Andersen
2022-07-21 1:54 ` Serge E. Hallyn
2022-07-27 15:44 ` Tycho Andersen
2022-07-27 16:32 ` Eric W. Biederman
2022-07-27 17:55 ` Tycho Andersen
2022-07-28 18:48 ` Eric W. Biederman
2022-07-27 17:55 ` Oleg Nesterov
2022-07-27 18:18 ` Tycho Andersen
2022-07-27 19:19 ` Oleg Nesterov
2022-07-27 19:40 ` Tycho Andersen [this message]
2022-07-28 9:12 ` Oleg Nesterov
2022-07-28 21:20 ` Tycho Andersen
2022-07-29 5:04 ` Eric W. Biederman
2022-07-29 13:50 ` Tycho Andersen
2022-07-29 16:15 ` Eric W. Biederman
2022-07-29 16:48 ` Tycho Andersen
2022-07-29 17:40 ` [RFC][PATCH] fuse: In fuse_flush only wait if someone wants the return code Eric W. Biederman
2022-07-29 20:47 ` Oleg Nesterov
2022-07-30 0:15 ` Al Viro
2022-07-30 5:10 ` [RFC][PATCH v2] " Eric W. Biederman
2022-08-01 15:16 ` Tycho Andersen
2022-08-02 12:50 ` Miklos Szeredi
2022-08-15 13:59 ` Tycho Andersen
2022-08-15 17:55 ` Serge E. Hallyn
2022-09-01 14:06 ` [PATCH] " Tycho Andersen
2022-09-19 15:03 ` Tycho Andersen
2022-09-20 18:02 ` Serge E. Hallyn
2022-09-26 14:17 ` Tycho Andersen
2022-09-27 9:46 ` Miklos Szeredi
2022-09-29 14:05 ` [fuse-devel] " Stef Bon
2022-09-29 16:39 ` [PATCH v2] " Tycho Andersen
2022-09-30 13:35 ` Miklos Szeredi
2022-09-30 14:01 ` Tycho Andersen
2022-09-30 14:41 ` Miklos Szeredi
2022-09-30 16:09 ` Tycho Andersen
2022-10-26 9:01 ` Miklos Szeredi
2022-11-14 16:02 ` [PATCH v3] " Tycho Andersen
2022-11-28 15:00 ` Tycho Andersen
2022-12-08 14:26 ` Miklos Szeredi
2022-12-08 17:49 ` Tycho Andersen
2022-12-19 19:16 ` Tycho Andersen
2023-01-03 14:51 ` Tycho Andersen
2023-01-05 15:15 ` Serge E. Hallyn
2023-01-26 14:12 ` Miklos Szeredi
2022-09-30 19:47 ` [PATCH] " Serge E. Hallyn
2022-09-19 15:46 ` [RFC][PATCH v2] " Eric W. Biederman
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