Messages in this thread | | | Date | Wed, 19 Sep 2018 16:01:01 +0800 | From | Ming Lei <> | Subject | Re: [PATCH 2/4] lib/percpu-refcount: introduce percpu_ref_resurge() |
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On Wed, Sep 19, 2018 at 03:55:07PM +0800, Ming Lei wrote: > On Wed, Sep 19, 2018 at 01:19:10PM +0800, jianchao.wang wrote: > > Hi Ming > > > > On 09/18/2018 06:19 PM, Ming Lei wrote: > > > + unsigned long __percpu *percpu_count; > > > + > > > + WARN_ON_ONCE(__ref_is_percpu(ref, &percpu_count)); > > > + > > > + /* get one extra ref for avoiding race with .release */ > > > + rcu_read_lock_sched(); > > > + atomic_long_add(1, &ref->count); > > > + rcu_read_unlock_sched(); > > > + } > > > > The rcu_read_lock_sched here is redundant. We have been in the critical section > > of a spin_lock_irqsave. > > Right. > > > > > The atomic_long_add(1, &ref->count) may have two result. > > 1. ref->count > 1 > > it will not drop to zero any more. > > 2. ref->count == 1 > > it has dropped to zero and .release may be running. > > IMO, both the two cases are fine and supported, or do you have other > concern about this way?
It is too quick, :-)
Yeah, the .release() may be running.
For blk-mq/NVMe's use case, it won't be an issue. We may comment on this race and let user handle it if it is a problem.
thanks, Ming
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