Oleg Nesterov (oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org) wrote:

On 12/21, Frederic Weisbecker wrote:

quoted

On Wed, Dec 21, 2011 at 11:24:13AM -0800, Mandeep Singh Baines wrote:

quoted

If you call exec from a thread other than g, g is now unlinked. So
"t != g" will always be true. If you then pthread_create, you now
have two threads so "t != __prev" will also always be true. So
you now have an infinite loop.

Oh you're right.

But then we can't use t != t->group_leader because that assumes while_each_thread()
started on the leader.

Yes, this can't work.

Besides, we need more burriers to rely on the ->group_leader check.

See http://marc.info/?t=127688987300002

I went through the thread. Were there any other concerns other than
requiring that you start with the group_leader and the barrier?

You could modify zap_other_threads to start with the group leader by
skipping p:

if (p == t)
   continue;

in particular, http://marc.info/?l=linux-kernel&m=127714242731448
I think this should work, but then we should do something with the
users like zap_threads().

With that patch, won't you potentially miss the exec thread if an exec
occurs while you're iterating over the list? Is that OK?

Regards,
Mandeep

Oleg.