Messages in this thread | | | Date | Wed, 24 Jan 2024 01:39:30 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH v2 0/2] getrusage: use sig->stats_lock |
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On 01/23, Dylan Hatch wrote: > > I have one last question -- is there possibly an edge case in which > the hard lockup > can still happen? How likely is it for many writers to force enough > readers to do a > retry on the seqlock, disabling irq and causing the lockup?
I don't know how likely is it, and I guess the repro should be more creative ;)
But yes. Please see the TODO: section in the changelog,
- Turn sig->stats_lock into seqcount_rwlock_t, this way the readers in the slow mode won't exclude each other.
and more importantly,
- stats_lock has to disable irqs because ->siglock can be taken in irq context, it would be very nice to change __exit_signal() to avoid the siglock->stats_lock dependency.
There are other users which take stats_lock under siglock (and the "fs/proc: do_task_stat" series changes 2 of them to not do this), but __exit_signal() is most problematic.
If we remove this dependency, we can turn read_seqbegin_or_lock_irqsave() into read_seqbegin_or_lock() which doesn't disable irqs.
Oleg.
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