[dm-devel] [PATCH 1/2] dm-snapshot: suspend origin when doing exception handover

[Mike Snitzer]

On Thu, Feb 26 2015 at 11:40am -0500,
Mikulas Patocka <mpatocka at redhat.com> wrote:

> In the function snapshot_resume we perform exception store handover. If
> there is another active snapshot target, the exception store is moved from
> this target to the target that is being resume.
> 
> The problem is that if there is some pending exception, it will point to
> an incorrect exception store after that handover, causing crash in BUG in
> dm-snap-persistent.c:get_exception - see bug 1177389.
> 
> This bug can be triggered by repeatedly changing snapshot permissions with
> "lvchange -p r" and "lvchange -p rw" while there are writes on the
> associated origin device.
> 
> To fix this bug, we must suspend the origin device when doing the
> exception store handover to make sure that there is no pending exception.
> 
> This patch:
> - introdices _origin_hash that keeps track of dm_origin structures.
> - introduces function __lookup_dm_origin, __insert_dm_origin and
>   __remove_dm_origin that manipulate the origin hash.
> - modifies snapshot_resume so that it calls dm_internal_suspend_fast and
>   dm_internal_resume_fast on the origin device.
> 
> Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>

I staged this for 4.0 here (note I bumped the target versions and
revised the header slightly):
https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-for-4.0&id=b735fede8d957d9d255e9c5cf3964cfa59799637