On 07/11, Eric W. Biederman wrote:
> Oleg Nesterov <o...@redhat.com> writes:
> >> -  recalc_sigpending();
> >> -  if (signal_pending(current)) {
> >> +  if (read_seqcount_retry(&current->signal->multi_process_seq, seq) ||
> >> +      fatal_signal_pending(current)) {
> >>            retval = -ERESTARTNOINTR;
> >>            goto bad_fork_cancel_cgroup;
> >
> > So once again, I think this is not right, see the discussion on
> > bugzilla.
> I am trying to dig through and understand your concerns.  I am having
> difficulty understanding your concerns.
> Do the previous patches look good to you?

Yes, yes, personally I like 1-10 after a quick glance. I'll try to read this
series carefully later, but I don't think I will find something really wrong.

> If I understand you correctly.  Your concern is that since we added the:
>       recalc_sigpending();
>         if (signal_pending(current))
>               return -ERESTARTNOINTR;
> Other (non-signal) code such as the freezer has come to depend upon that
> test.  Changing the test in the proposed way will allow the new child to
> escape the freezer, as it is not guaranteed the new child will be
> frozen.


> It seems reasonable to look at other things that set TIF_SIGPENDING and
> see if any of them are broken by the fork changes.

Again, please look at do_signal_stop(). If it was the source of 
copy_process() should fail. Or we should update the new thread to participate in
group-stop, but then we need to set TIF_SIGPENDING, copy the relevant part of
current->jobctl, and increment ->group_stop_count at least.

> A practical (and fixable) problem with your patch was that you modified
> task->blocked which was then copied to the child.  So all children now
> would start with all signals being blocked.

What are you talking about, this pseudo-code has a lot more bugs ;)

OK, at least I certainly agree that this approach needs more changes in 

> > This also makes another difference in multi-threaded case, a signal with a 
> > handler
> > sent to a forking process will be re-targeted to another thread which can 
> > handle it;
> > with your patch this signal will be "blocked" until fork() finishes or 
> > until another
> > thread gets TIF_SIGPENDING. Not that I think this is that important,
> > but still.
> I would not object to wants_signal deciding that a task in the middle of
> copy_process does not want signals.

This is not enough, we need to signal all in-fork threads...


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