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

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Message-ID: <5732F607.3030504@linaro.org>
Date:	Wed, 11 May 2016 11:06:15 +0200
From:	Paolo <paolo.valente@...aro.org>
To:	Nikolay Borisov <kernel@...p.com>, 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

Il 11/05/2016 08:43, Nikolay Borisov ha scritto:
>
>
> 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.
>

Definitely (I didn't do that in the first place, because I worried
only about doing the association when bio_clone_fast was certainly
successful).

I'm sending a fresh patch.

Thanks,
Paolo

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