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SubjectRe: regression introduced by - timers: fix itimer/many thread hang
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> But please note that currently this already happens for sub-threads (and
> if we protect ->signal with rcu too), the exiting sub-thread does not
> contribute to accounting after release_task(self). Also, when the last
> thread exits the process can be reaped by its parent, but after that
> the threads can still use CPU.

Understood (I think I mentioned this earlier). All this is what makes it
seem potentially attractive in the long run to reorganize this more thoroughly.

> > Yes, I think you're right. The best solution that comes to mind off hand
> > is to protect the update/read of that u64 with a seqcount_t on 32-bit.
>
> Oh, but we need them to be per-cpu, and both read and write need memory
> barriers... Not that I argue, this will fix the problem of course, just
> I don't know how this impacts the perfomance.

I agree it's a sticky question. Just the only thing I've thought of so far.


Thanks,
Roland


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