linux-kernel - Re: [PATCH BUGFIX V4] block: add missing group association in bio-cloning functions

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Date:	Tue, 7 Jun 2016 09:09:08 +0200
From:	Paolo <paolo.valente@...aro.org>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>,
	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 V4] block: add missing group association in
 bio-cloning functions

Jens,
are you picking this fix?

Thanks,
Paolo

Il 13/05/2016 22:42, Jeff Moyer ha scritto:
> Paolo Valente <paolo.valente@...aro.org> writes:
>
>> 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>
>> Reviewed-by: Nikolay Borisov <kernel@...p.com>
>
> I think this one's golden!  Thanks, Paolo!
>
> Reviewed-by: Jeff Moyer <jmoyer@...hat.com>
>
>
>> ---
>> Tejun: I didn't add also your Ack, just because this version is slightly
>> different from the one you acked.
>> ---
>>   block/bio.c          | 15 +++++++++++++++
>>   fs/btrfs/extent_io.c |  6 ------
>>   include/linux/bio.h  |  3 +++
>>   3 files changed, 18 insertions(+), 6 deletions(-)
>>
>> diff --git a/block/bio.c b/block/bio.c
>> index 807d25e..89f517c 100644
>> --- a/block/bio.c
>> +++ b/block/bio.c
>> @@ -590,6 +590,8 @@ void __bio_clone_fast(struct bio *bio, struct bio *bio_src)
>>   	bio->bi_rw = bio_src->bi_rw;
>>   	bio->bi_iter = bio_src->bi_iter;
>>   	bio->bi_io_vec = bio_src->bi_io_vec;
>> +
>> +	bio_clone_blkcg_association(bio, bio_src);
>>   }
>>   EXPORT_SYMBOL(__bio_clone_fast);
>>
>> @@ -695,6 +697,8 @@ integrity_clone:
>>   		}
>>   	}
>>
>> +	bio_clone_blkcg_association(bio, bio_src);
>> +
>>   	return bio;
>>   }
>>   EXPORT_SYMBOL(bio_clone_bioset);
>> @@ -2016,6 +2020,17 @@ void bio_disassociate_task(struct bio *bio)
>>   	}
>>   }
>>
>> +/**
>> + * bio_clone_blkcg_association - clone blkcg association from src to dst bio
>> + * @dst: destination bio
>> + * @src: source bio
>> + */
>> +void bio_clone_blkcg_association(struct bio *dst, struct bio *src)
>> +{
>> +	if (src->bi_css)
>> +		WARN_ON(bio_associate_blkcg(dst, src->bi_css));
>> +}
>> +
>>   #endif /* CONFIG_BLK_CGROUP */
>>
>>   static void __init biovec_init_slabs(void)
>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
>> index d247fc0..19f6739 100644
>> --- a/fs/btrfs/extent_io.c
>> +++ b/fs/btrfs/extent_io.c
>> @@ -2686,12 +2686,6 @@ struct bio *btrfs_bio_clone(struct bio *bio, gfp_t gfp_mask)
>>   		btrfs_bio->csum = NULL;
>>   		btrfs_bio->csum_allocated = NULL;
>>   		btrfs_bio->end_io = NULL;
>> -
>> -#ifdef CONFIG_BLK_CGROUP
>> -		/* FIXME, put this into bio_clone_bioset */
>> -		if (bio->bi_css)
>> -			bio_associate_blkcg(new, bio->bi_css);
>> -#endif
>>   	}
>>   	return new;
>>   }
>> diff --git a/include/linux/bio.h b/include/linux/bio.h
>> index 6b7481f..16cbe59 100644
>> --- a/include/linux/bio.h
>> +++ b/include/linux/bio.h
>> @@ -527,11 +527,14 @@ extern unsigned int bvec_nr_vecs(unsigned short idx);
>>   int bio_associate_blkcg(struct bio *bio, struct cgroup_subsys_state *blkcg_css);
>>   int bio_associate_current(struct bio *bio);
>>   void bio_disassociate_task(struct bio *bio);
>> +void bio_clone_blkcg_association(struct bio *dst, struct bio *src);
>>   #else	/* CONFIG_BLK_CGROUP */
>>   static inline int bio_associate_blkcg(struct bio *bio,
>>   			struct cgroup_subsys_state *blkcg_css) { return 0; }
>>   static inline int bio_associate_current(struct bio *bio) { return -ENOENT; }
>>   static inline void bio_disassociate_task(struct bio *bio) { }
>> +static inline void bio_clone_blkcg_association(struct bio *dst,
>> +			struct bio *src) { return 0; }
>>   #endif	/* CONFIG_BLK_CGROUP */
>>
>>   #ifdef CONFIG_HIGHMEM