On 2/1/21 10:40 AM, Chao Leng wrote:

On 2021/2/1 16:57, Hannes Reinecke wrote:

quoted

On 2/1/21 9:47 AM, Chao Leng wrote:

quoted

On 2021/2/1 15:29, Hannes Reinecke wrote:[ .. ]

quoted

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.

Ah. So this should be better:

@@ -202,10 +202,12 @@ static struct nvme_ns *__nvme_find_path(struct 

nvme_ns_head *head, int node)
  static struct nvme_ns *nvme_next_ns(struct nvme_ns_head *head,
                 struct nvme_ns *ns)
  {
-       ns = list_next_or_null_rcu(&head->list, &ns->siblings, struct 
nvme_ns,
-                       siblings);
-       if (ns)
-               return ns;
+       if (ns && !test_bit(NVME_NS_REMOVING, &ns->flags)) {
+               ns = list_next_or_null_rcu(&head->list, &ns->siblings,
+                                          struct nvme_ns, siblings);
+               if (ns)
+                       return ns;
+       }
         return list_first_or_null_rcu(&head->list, struct nvme_ns, 
siblings);
  }

The 'NVME_NS_REMOVING' bit is set before list_del_rcu() is called, so it 
should guard against the issue you mentioned.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

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