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

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Date:	Wed, 11 May 2016 09:43:06 +0300
From:	Nikolay Borisov <kernel@...p.com>
To:	Paolo Valente <paolo.valente@...aro.org>,
	Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>
Cc:	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	ulf.hansson@...aro.org, linus.walleij@...aro.org,
	broonie@...nel.org, stable@...r.kernel.org
Subject: Re: [PATCH BUGFIX V3] block: add missing group association in
 bio-cloning functions



On 05/11/2016 09:38 AM, Nikolay Borisov wrote:
> 
> 
> 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@...aro.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.

Right, to correct myself: You might want to move the association to
__blk_clone_fast that way you are also covering dm devices as well as
users of bio_clone_fast.


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