[Devel] [PATCH hci-8.1 v2] dm table: don't inherit live table's type for request-based tables

[no-reply at sashiko.virtuozzo.com]

> A request-based table without devices inherits the live table's type
> in dm_table_determine_type(). Since commit 6936c12cf809 ("dm table: fix
> 'all_blk_mq' inconsistency when an empty table is loaded") this
> includes bio-based types, although the inheritance was meant to pick a
> variant of the request-based type, and only one is left now. So a
> request-based table loaded over a bio-based device becomes bio-based,
> which its target cannot serve.
> 
> dm-qcow2 and dm-ploop open their images by fd and never call
> dm_get_device(). Loaded over a bio-based device they have no ->map, and
> the first bio calls a NULL ->map from __map_bio():
> 
>   BUG: kernel NULL pointer dereference, address: 0000000000000000
>   RIP: 0010:0x0
>    __map_bio+0x197/0x1c0 [dm_mod]
> [ ... ]
> "can't change device type", as it does for request-based tables with
> devices.
> 
> https://virtuozzo.atlassian.net/browse/VSTOR-150573
> Signed-off-by: Alexander Ivanov <alexander.ivanov at virtuozzo.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.vzint.dev/#/patchset/20261020075243.1283345-1-alexander.ivanov@virtuozzo.com?part=1