On 01/04, Mandeep Singh Baines wrote:

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

quoted

On 12/21, Frederic Weisbecker wrote:

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

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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;

Yes, we can but there are other while_each_thread(nonleader) users.
Yes we can fix them too but this looks a bit ugly and we need to
change while_each_thread() anyway. And I do not see why this change
will be simpler if we restrict it to group_leader.

And note that zap_other_threads() is fine in any case, it is called
under ->siglock.

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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?

Of course it is not OK ;) Note the "we should do something with" above.

Oleg.