Messages in this thread | | | Date | Mon, 15 Aug 2011 21:09:35 +0200 | From | Oleg Nesterov <> | Subject | Re: Possible race between cgroup_attach_proc and de_thread, and questionable code in de_thread. |
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On 08/15, NeilBrown wrote: > > de_thread can change the group_leader of a thread_group, and release_task can > remove a non-leader while leaving the rest of the thread_group intact. So > any while_each_thread() loop needs some extra care to ensure that it doesn't > loop infinitely, because the "head" that it is looking for might not be there > any more. > Maybe there are other rules that ensure this can never happen, but they sure > aren't obvious to me (i.e. if you know them - please tell ;-)
No, I don't know ;)
And note also that if g != leader, then while_each_thread(g, t) can hang simply because g exits. I am still trying to invent something simple to fix while_each_thread-under-rcu.
This looks possible, but I am starting to think that, say, zap_threads() needs locking anyway. With any fix I can imagine, it can miss a thread we should care about.
Oleg.
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