Re: [PATCH v2] signal: Adjust error codes according to restore_user_sigmask()

[Oleg Nesterov]

On 05/23, David Laight wrote:
>
> From: Oleg Nesterov
> > On 05/23, David Laight wrote:
> > >
> > > I'm confused...
> >
> > Me too. To clarify, the current code is obviously buggy, pselect/whatever
> > shouldn't return 0 (or anything else) if it was interrupted and we are going
> > to deliver the signal.
>
> If it was interrupted the return value has to be EINTR.

Yes, and this is what we need to fix.

> Whether any signal handlers are called is a separate matter.

Not really... because in this case we know that the signal will be delivered,

> > Not sure I understand... OK, suppose that you do
> >
> > 	block-all-signals;
> > 	ret = pselect(..., sigmask(SIG_URG));
> >
> > if it returns success/timeout then the handler for SIG_URG should not be called?
>
> Ugg...
> Posix probably allows the signal handler be called at the point the event
> happens rather than being deferred until the system call completes.
> Queueing up the signal handler to be run at a later time (syscall exit)
> certainly makes sense.
> Definitely safest to call the signal handler even if success/timeout
> is returned.

Why?

> pselect() exists to stop the entry race, not the exit one.

pselect() has to block SIG_URG again before it returns to user-mode, right?

Suppose pselect() finds a ready fd, and this races with SIG_URG.

Why do you think the handler should run?

What if SIG_URG comes right after pselect() blocks SIG_URG again? I mean,
how this differs the case when it comes before, but a ready fd was already
found?

Oleg.