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

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

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.

Cheers,

Hannes

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