Re: [PATCH v2] nvme-multipath: Early exit if no path is available

[Hannes Reinecke]

On 1/28/21 10:18 AM, Chao Leng wrote:
> On 2021/1/28 15:58, Daniel Wagner wrote:
> > On Thu, Jan 28, 2021 at 09:31:30AM +0800, Chao Leng wrote:
> > > > --- a/drivers/nvme/host/multipath.c
> > > > +++ b/drivers/nvme/host/multipath.c
> > > > @@ -221,7 +221,7 @@ static struct nvme_ns 
> > > > *nvme_round_robin_path(struct nvme_ns_head *head,
> > > >        }
> > > >        for (ns = nvme_next_ns(head, old);
> > > > -         ns != old;
> > > > +         ns && ns != old;
> > > nvme_round_robin_path just be called when !"old".
> > > nvme_next_ns should not return NULL when !"old".
> > > It seems unnecessary to add checking "ns".
> >
> > The problem is when we enter nvme_round_robin_path() and there is no
> > path available. In this case the initialization ns = nvme_next_ns(head,
> > old) could return a NULL pointer."old" should not be NULL, so there is 
> > at least one path that is "old".
> It is impossible to return NULL for nvme_next_ns(head, old).

No. list_next_or_null_rcu()/list_first_or_null_rcu() will return NULL 
when then end of the list is reached.

Cheers,

Hannes
--
Dr. Hannes Reinecke                Kernel Storage Architect
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