[dm-devel] LVM snapshot broke between 4.14 and 4.16

[Mike Snitzer]

On Thu, Aug 02 2018 at  5:52pm -0400,
Linus Torvalds <torvalds at linux-foundation.org> wrote:

> On Thu, Aug 2, 2018 at 2:39 PM WGH <wgh at torlan.ru> wrote:
> >
> > I've just found one public report of this bug, though:
> > https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=900442
> 
> Yeah, it does sound like we should fix this issue.

Debian is notorious for having a stale and/or custom lvm2.
Generally speaking, it is recommended that lvm2 not be older than the
kernel (but the opposite is fine).  

Given the narrow scope of users impacted (read-only snapshot creation is
very niche, certainly not the default): I don't think it is worth making
fiddly changes in dm-snapshot to warn the user and override the
permissions for the cow device.

Mike