Re: [PATCH] signal: don't silently convert SI_USER signals to non-current pidfd

[Oleg Nesterov <oleg@redhat.com>]

On 04/17, Christian Brauner wrote:
>
> On Wed, Apr 17, 2019 at 03:16:03PM +0200, Oleg Nesterov wrote:
> > On 04/17, Christian Brauner wrote:
> > >
> > > On Mon, Apr 08, 2019 at 03:13:16PM +0200, Oleg Nesterov wrote:
> > > >
> > > > but perhaps it should always fail, even if task_pid(current) == pid.
> > > >
> > > > sys_rt_sigqueueinfo() allows to send any siginfo to yourself, but this is only needed
> > > > for checkpoint/restart.
> > >
> > > Yes, that's why this was added. I would leave it in exactly because of
> > > checkpoint/restart.
> >
> > I don't understand...
> >
> > c/r doesn't need this "feature" in pidfd_send_signal(), so it can be removed.
> > But,
>
> Just out of curiosity: in what sense? They don't need it since they have
> other ways of doing this

Yes. The restarting process needs to "restore" the pending signals, including the
signals with si_code >= 0. It does this using tgsigqueueinfo() and that is why we
allow this if the signal sent to itself.

So criu simply doesn't need pidfd_send_signal() to do this. And at the same time,

> or they *can't* use it for some other reason

Yes again. pidfd_send_signal() does kill_pid_info(), so it can't be used to restore
the "per-thread" task->pending signals.

Oleg.