Messages in this thread | | | Date | Tue, 3 Jul 2018 13:24:24 -0700 | From | Tejun Heo <> | Subject | Re: [PATCH] cgroup: use irqsave in cgroup_rstat_flush_locked() |
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(cc'ing Peter and Ingo for lockdep)
Hello, Sebastian.
On Tue, Jul 03, 2018 at 06:45:44PM +0200, Sebastian Andrzej Siewior wrote: > All callers of cgroup_rstat_flush_locked() acquire cgroup_rstat_lock > either with spin_lock_irq() or spin_lock_irqsave().
So, irq is always disabled in cgroup_rstat_flush_locked().
> cgroup_rstat_flush_locked() itself acquires cgroup_rstat_cpu_lock which > is a raw_spin_lock. This lock is also acquired in cgroup_rstat_updated() > in IRQ context and therefore requires _irqsave() locking suffix in > cgroup_rstat_flush_locked().
Yes, the cpu locks should be irqsafe too; however, as irq is always disabled in that function, save/restore is redundant, no?
> Since there is no difference between spin_lock_t and raw_spin_lock_t > on !RT lockdep does not complain here. On RT lockdep complains because > the interrupts were not disabled here and a deadlock is possible.
We at least used to do this in the kernel - manipulating irqsafe locks with spin_lock/unlock() if the irq state is known, whether enabled or disabled, and ISTR lockdep being smart enough to track actual irq state to determine irq safety. Am I misremembering or is this different on RT kernels?
Thanks.
-- tejun
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