linux-kernel - Re: LVM snapshot broke between 4.14 and 4.16

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Date:   Fri, 3 Aug 2018 09:31:03 -0400
From:   Mike Snitzer <snitzer@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     wgh@...lan.ru, Ilya Dryomov <idryomov@...il.com>,
        Jens Axboe <axboe@...nel.dk>,
        linux-block <linux-block@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sagi Grimberg <sagi@...mberg.me>, dm-devel@...hat.com
Subject: Re: LVM snapshot broke between 4.14 and 4.16

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

> On Thu, Aug 2, 2018 at 2:39 PM WGH <wgh@...lan.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