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

[Sagi Grimberg]

>> The revalidation is still required there in order to update the blockdev
>> size when multipath is enabled. With this revert, the behavior regressed
>> back to before fab7772bfbcf, so the size isn't updated under multipath
>> when the device is in use (e.g. mounted), it will only be effectively
>> updated next time it is mounted as a side-effect of blkdev_open on first
>> opener. This prevents online resizing of filesystems.
>>
>>> 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.
>>
>> The mpath gendisk doesn't have a revalidate_disk fop indeed, but call to
>> check_disk_size_change was needed to update its size. Otherwise, the
>> size change isn't reflected externally to userspace before next mount.
>> cb224c3af4df doesn't fix this as it skips revalidate and thus also skips
>> updating the size.
>>
>> The issue is that under CONFIG_NVME_MULTIPATH=y the ns->disk becomes a
>> hidden gendisk (see nvme_set_disk_name) and thus doesn't have a backing
>> bdev, while ns->head->disk becomes the "visible" one to userspace (with
>> a backing bdev), and therefore needs its bdev->bd_inode->i_size updated
>> when resized.
>>
>> The following patch seems to be working, although I'm not sufficiently
>> familiar with the code to tell if this won't cause any other deadlocks
>> with some confidence:
> 
> This looks sensible to me.  Sagi?

Looks sensible to me too, but let's add a comment to clarify the 
existence of this please.