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

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Message-ID: <x49vb2h7kqb.fsf@segfault.boston.devel.redhat.com>
Date:	Fri, 13 May 2016 16:42:52 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Paolo Valente <paolo.valente@...aro.org>
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

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