Re: while_each_thread() under rcu_read_lock() is broken?

[Roland McGrath]

I think you're right.  I can't see what would prevent that race.  

So for_each_process and do_each_thread are safe only under
read_lock(&tasklist_lock) and while_each_thread is only safe under
either that or siglock.  (Also a few places using next_thread in
similar loops outside those macros.)

Perhaps we could move those del's from __unhash_process to
__put_task_struct (or just delayed_put_task_struct?) and then
they wouldn't need to be rculist.h calls after all.  But we
would a need careful audit to figure out the assumptions about
being on the list meaning not reaped yet.

I think de_thread() in exec-by-nonleader is the only case where this
can happen, right?  So then perhaps we could make it call release_task
only via call_rcu?


Thanks,
Roland
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