Re: epoll oops.

[Eric Wong]

Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> Yes. Before that 971316f0503a hack epoll can't even know if the task
> which did signalfd_poll() exits and frees the active signalfd_wqh.
> If for example that task forked a child before exit.
> 
> And the whole RCU logic is only needed if exit/ep_remove_wait_queue
> actually race with each other.

Is there any chance this oops is caused by (or at least more easily
exposed by) commit 91cf5ab60ff82ecf4550a596867787c1e360dd3f ?
(epoll: add a reschedule point in ep_free())

I thought 91cf5ab would be benign, except...

> Yes, ugly, agreed. d80e731ecab4 even tries to docunent that this all
> is the hack.

.. the following sentence from d80e731ecab4 caught my eye:

    It also assumes that nobody can take tasklist_lock under epoll
    locks, this seems to be true.

I haven't been able to trace if cond_resched() can take tasklist_lock.
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