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

[Chao Leng]

On 2021/2/1 16:57, Hannes Reinecke wrote:
> On 2/1/21 9:47 AM, Chao Leng wrote:
> > On 2021/2/1 15:29, Hannes Reinecke wrote:[ .. ]
> > > Urgh. Please, no. That is well impossible to debug.
> > > Can you please open-code it to demonstrate where the difference to the current (and my fixed) versions is?
> > > I'm still not clear where the problem is once we applied both patches.
> > For example assume the list has three path, and all path is not NVME_ANA_OPTIMIZED:
> > head->next = ns1;
> > ns1->next = ns2;
> > ns2->next = head;
> > old->next = ns2;
> And this is where I have issues with.
> Where does 'old' come from?
> Clearly it was part of the list at one point; so what happened to it?
I explained this earlier.
In nvme_ns_remove, there is a hole between list_del_rcu and
nvme_mpath_clear_current_path. If head->current_path is the "old", and
the "old" is removing. The "old" is already removed from the list by
list_del_rcu, but head->current_path is not clear to NULL by
nvme_mpath_clear_current_path.
Find path is race with nvme_ns_remove, use the "old" pass to
nvme_round_robin_path to find path.
> Cheers,
>
> Hannes