From: Tycho Andersen <tycho@tycho.pizza>
To: "Serge E. Hallyn" <serge@hallyn.com>
Cc: "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, 20 Jul 2022 14:58:42 -0600 [thread overview]
Message-ID: <YthsgqAZYnwHZLn+@tycho.pizza> (raw)
In-Reply-To: <20220720150328.GA30749@mail.hallyn.com>
On Wed, Jul 20, 2022 at 10:03:28AM -0500, Serge E. Hallyn wrote:
> On Wed, Jul 13, 2022 at 11:53:05AM -0600, Tycho Andersen wrote:
> > The wait_* code uses signal_pending_state() to test whether a thread has
> > been interrupted, which ultimately uses __fatal_signal_pending() to detect
> > if there is a fatal signal.
> >
> > When a pid ns dies, it does:
> >
> > group_send_sig_info(SIGKILL, SEND_SIG_PRIV, task, PIDTYPE_MAX);
> >
> > for all the tasks in the pid ns. That calls through:
> >
> > group_send_sig_info() ->
> > do_send_sig_info() ->
> > send_signal_locked() ->
> > __send_signal_locked()
> >
> > which does:
> >
> > pending = (type != PIDTYPE_PID) ? &t->signal->shared_pending : &t->pending;
> >
> > which puts sigkill in the set of shared signals, but not the individual
> > pending ones. When complete_signal() is called at the end of
> > __send_signal_locked(), if the task already had PF_EXITING (i.e. was
> > already waiting on something in its fd closing path like a fuse flush),
> > complete_signal() will not wake up the thread, since wants_signal() checks
> > PF_EXITING before testing for SIGKILL.
> >
> > If tasks are stuck in a killable wait (e.g. a fuse flush operation), they
> > won't see this shared signal, and will hang forever, since TIF_SIGPENDING
> > is set, but the fatal signal can't be detected. So, let's also look for
> > PF_EXITING in __fatal_signal_pending().
> >
> > Signed-off-by: Tycho Andersen <tycho@tycho.pizza>
>
> Cool, thanks for nailing this down!
>
> I assume you've been running this on some boxes with no weird effects?
Yes, but I haven't tested all the paths.
> > ---
> > include/linux/sched/signal.h | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
> > index cafbe03eed01..c20b7e1d89ef 100644
> > --- a/include/linux/sched/signal.h
> > +++ b/include/linux/sched/signal.h
> > @@ -402,7 +402,8 @@ static inline int signal_pending(struct task_struct *p)
> >
> > static inline int __fatal_signal_pending(struct task_struct *p)
> > {
> > - return unlikely(sigismember(&p->pending.signal, SIGKILL));
> > + return unlikely(sigismember(&p->pending.signal, SIGKILL) ||
> > + p->flags & PF_EXITING);
>
> Looking around at the callers this does seem safe, but the name does
> now seem misleading. Should this be renamed to something like
> exiting_or_fatal_signal_pending()?
This is why I like my original patch better: it is just expanding the
set of signals to include the shared signals, which are indeed still
fatal pending signals for the task. I don't really understand Eric's
argument about kernel threads ignoring SIGKILL, since kernel threads
can still ignore SIGKILL just fine after this patch.
But yes, assuming Eric is ok with this venison. I can send a v2 with
the name change as you suggest.
Thanks for looking.
Tycho
next prev parent reply other threads:[~2022-07-20 20:59 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 [this message]
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
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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