Re: Fix signalfd interaction with thread-private signals

Oleg Nesterov
2007-06-23T16:35:29Z

On 06/22, Linus Torvalds wrote:
>
> On Sat, 23 Jun 2007, Benjamin Herrenschmidt wrote:
> >
> > >
> > > It does exactly so, please note this chunk
> > >
> > > @@ -330,7 +339,7 @@ asmlinkage long sys_signalfd(int ufd, si
> > >
> > > init_waitqueue_head(&ctx->wqh);
> > > ctx->sigmask = sigmask;
> > > - ctx->tsk = current;
> > > + ctx->tsk = current->group_leader;
> > >
> > > > It might well be that signalfd's concept of context is wrong in the
> > > > first place and it should be attached to processes rather than threads
> > > > and that made more explicit in the first place...
> >
> > Yup, looks like I was looking at a wrong patch... I think it's the right
> > thing to do indeed.
>
> Quite frankly, it strikes me that if we want to do this, then we shouldn't
> save the _process_ information at all, we should save the "sighand"
> instead.

Yes, unless we pass signalfd to another process.

> So either we save the process info, or we save the sighand, but saving the
> "group_leader" seems totally bogus. Especially as the group leader can
> change (by execve()).

Note that exec() can change ->sighand as well, so in general this can't help.

Currently not a problem, exec() detaches process from signalfd anyway.

This reminds me, we have a similar problem with !CPUCLOCK_PERTHREAD()
cpu-timers, iirc. They can survive after exec(), but only if it was
->group_leader who does exec.

Oleg.