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

[Sagi Grimberg]

> > > > You can't see exactly where it dies but I followed the assembly to
> > > > nvme_round_robin_path(). Maybe it's not the initial nvme_next_ns(head,
> > > > old) which returns NULL but nvme_next_ns() is returning NULL eventually
> > > > (list_next_or_null_rcu()).
> > > So there is other bug cause nvme_next_ns abormal.
> > > I review the code about head->list and head->current_path, I find 2 bugs
> > > may cause the bug:
> > > First, I already send the patch. see:
> > > https://lore.kernel.org/linux-nvme/20210128033351.22116-1-lengchao@xxxxxxxxxx/ 
> > >
> > > Second, in nvme_ns_remove, list_del_rcu is before
> > > nvme_mpath_clear_current_path. This may cause "old" is deleted from the
> > > "head", but still use "old". I'm not sure there's any other
> > > consideration here, I will check it and try to fix it.
> >
> > The reason why we first remove from head->list and only then clear
> > current_path is because the other way around there is no way
> > to guarantee that that the ns won't be assigned as current_path
> > again (because it is in head->list).
> ok, I see.
> > nvme_ns_remove fences continue of deletion of the ns by synchronizing
> > the srcu such that for sure the current_path clearance is visible.
> The list will be like this:
> head->next = ns1;
> ns1->next = head;
> old->next = ns1;
> This may cause infinite loop in nvme_round_robin_path.
> for (ns = nvme_next_ns(head, old);
>      ns != old;
>      ns = nvme_next_ns(head, ns))
> The ns will always be ns1, and then infinite loop.

Who is being removed? I'm not following