On Thu, Jan 26, 2017 at 5:17 AM, Christoph Hellwig [off-list ref] wrote:

On Thu, Jan 26, 2017 at 11:06:53AM +0100, Jan Kara wrote:

quoted

Yeah, so my patches (and I suspect your as well), have a problem when the
backing_device_info stays around because blkdev inode still exists, device
gets removed (e.g. USB disk gets unplugged) but blkdev inode still stays
around (there doesn't appear to be anything that would be forcing blkdev
inode out of cache on device removal and there cannot be because different
processes may hold inode reference) and then some other device gets plugged
in and reuses the same MAJOR:MINOR combination. Things get awkward there, I
think we need to unhash blkdev inode on device removal but so far I didn't
make this work...

The other option is to simply not release the dev_t until the backing_dev
is gone.

I came to a similar conclusion here:

   https://marc.info/?l=linux-scsi&m=147103737421897&w=4

James had some concerns, but I think its now clear this problem is
bigger than something we can fix locally in scsi.