APPLIED: [SRU F/Unstable 0/1] Handle I/O on a blk device without request function

[Seth Forshee]

On Thu, Jan 23, 2020 at 10:33:02AM +0200, Stefan Bader wrote:
> This is to handle a situation which only recently started to be
> exercised but the underlying breakage has been around since 4.1
> (Xenial onwards).
> 
> The plan is to try getting this upstream and backported via
> stable as it is nothing that will happen accidental in a normal
> workflow.
> 
> Just for the background, this was observed when uc20 started to
> support encrypted devices. During the initial setup, when the
> encrypted device is created, there is a short period of time
> (cryptsetup luksOpen does under the hood have first the device-
> mapper target without a mapping table and then supply the mapping)
> where the logical block device is around but has no function set up
> to do the I/O mapping. This stage already fires a uvent about the
> block device being added and this is acted on by a udev rule which
> only takes action when inside a snap, and this action attempts a
> mount which sends I/O to detect which (or wheteher) filesystem is
> on the block device/partition. And that causes a kernel crash.

Applied to focal/master-next and unstable/master, thanks!