[dm-devel] dm mirror: fix crash caused by NULL-pointer dereference

[Mike Snitzer]

On Mon, Jun 26 2017 at  7:49am -0400,
Zdenek Kabelac <zkabelac at redhat.com> wrote:

> Dne 26.6.2017 v 12:55 Eric Ren napsal(a):
> >Hi Zdenek,
> >
> >
> >On 06/26/2017 05:46 PM, Zdenek Kabelac wrote:
> >>Dne 26.6.2017 v 11:08 Eric Ren napsal(a):
> >>>
> >>[... snip...]
> >>
> >>Hi
> >>
> >>Which kernel version is this ?
> >>
> >>I'd thought we've already fixed this BZ for old mirrors:
> >>https://bugzilla.redhat.com/show_bug.cgi?id=1382382
> >>
> >>There similar BZ for md-raid based mirrors (--type raid1)
> >>https://bugzilla.redhat.com/show_bug.cgi?id=1416099
> >My base kernel version is 4.4.68, but with this 2 latest fixes applied:
> >
> >"""
> >Revert "dm mirror: use all available legs on multiple failures"
> 
> Ohh  - I've -rc6 - while this  'revert' patch went to 4.12-rc7.
> 
> I'm now starting to wonder why?
> 
> It's been a real fix for a real issue - and 'revert' message states
> there is no such problem ??
> 
> I'm confused....
> 
> Mike  - have you tried the sequence from BZ  ?

Jon (cc'd) tested it and found that the original issue wasn't
reproducible.  But that the commit in question was the source of crashes
(likely due to needing the fix from this thread).

We can revisit for 4.13 -- but I'll defer to Heinz.

Eric, please share your results from testing the latest 4.12-rc7.

Mike