Re: [PATCH v4 2/2] nbd: fix possible page fault for nbd disk

[Mike Christie <mchristi@redhat.com>]

On 09/17/2019 01:40 PM, Josef Bacik wrote:
>>> +		nbd->destroy_complete = &destroy_complete;
>>
>> Also, without the mutex part of the v3 patch, we could race and
>> nbd_dev_remove could have passed the destroy_complete check already, so
>> below we will wait forever.
>>
> 
> Oh hmm you're right,

I think I am actually wrong about that part too now :) I had forgot
about the idr removal under the mutex when making my original comment.

If nbd_put grabs the mutex first then it will do idr_remove under the
mutex. If nbd_genl_connect then runs, idr_find/idr_for_each will fail
and we will allocate a new nbd device and NBD_DISCONNECT_REQUESTED will
not be set.

If nbd_genl_connect grabs the mutex first, then idr_find/idr_for_each
will succeed and we will set the completion. nbd_put will then grab the
mutex and call nbd_remove_dev and see the completion.