Re: [PATCH BUGFIX V3] block: add missing group association in bio-cloning functions

[Nikolay Borisov <kernel@kyup.com>]

On 05/11/2016 01:01 AM, Paolo Valente wrote:
> When a bio is cloned, the newly created bio must be associated with
> the same blkcg as the original bio (if BLK_CGROUP is enabled). If
> this operation is not performed, then the new bio is not associated
> with any group, and the group of the current task is returned when
> the group of the bio is requested.
> 
> Depending on the cloning frequency, this may cause a large
> percentage of the bios belonging to a given group to be treated
> as if belonging to other groups (in most cases as if belonging to
> the root group). The expected group isolation may thereby be broken.
> 
> This commit adds the missing association in bio-cloning functions.
> 
> Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
> ---
>  block/bio.c          | 15 +++++++++++++++
>  fs/btrfs/extent_io.c |  6 ------
>  include/linux/bio.h  |  3 +++
>  3 files changed, 18 insertions(+), 6 deletions(-)
> 

Just for reference something like that was already proposed (and tested)
before, though it never got merged :

https://www.redhat.com/archives/dm-devel/2016-March/msg00007.html

So you might also want to patch __bio_clone_fast to also apply this for
dm backed devices.

Otherwise:

Reviewed-by: Nikolay Borisov <kernel@kyup.com>