[PATCH v2 for-5.8-rc 1/6] nvme: fix possible deadlock when I/O is blocked

[Sagi Grimberg]

>>>> Revert fab7772bfbcf ("nvme-multipath: revalidate nvme_ns_head gendisk
>>>> in nvme_validate_ns")
>>>>
>>>> When adding a new namespace to the head disk (via nvme_mpath_set_live)
>>>> we will see partition scan which triggers I/O on the mpath device node.
>>>> This process will usually be triggered from the scan_work which holds
>>>> the scan_lock. If I/O blocks (if we got ana change currently have only
>>>> available paths but none are accessible) this can deadlock on the head
>>>> disk bd_mutex as both partition scan I/O takes it, and head disk revalidation
>>>> takes it to check for resize (also triggered from scan_work on a different
>>>> path). See trace [1].
>>>>
>>>> This is no longer needed since commit cb224c3af4df ("nvme: Convert to
>>>> use set_capacity_revalidate_and_notify") which already updates resize
>>>> info without unnecessarily revalidating the disk.
>>>
>>> Did you look if any other revalidation gets skipped this way? E.g.
>>> LBA size change?
>>>
>>>   From purely the size POV this looks good, though.
>>
>> The only reason the revalidate was added was to update on a size change,
>> which is redundant.
>>
>> And if you look at revalidate, it only calls fops->revalidate_disk
>> (which is a noop in the mpath device) and checks the size change.
> 
> Please add this blurb to the changelog for the next version.

Will do. thanks