Paolo Valente <paolo.vale...@linaro.org> writes:
> When a bio is split, 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 frequency of splits, 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 then broken.
>
> This commit adds the missing association in bio_split.
>
> Signed-off-by: Paolo Valente <paolo.vale...@linaro.org>
> ---
> block/bio.c | 15 +++++++++++++++
> include/linux/bio.h | 2 ++
> 2 files changed, 17 insertions(+)
>
> diff --git a/block/bio.c b/block/bio.c
> index 807d25e..20795eb 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1811,6 +1811,8 @@ struct bio *bio_split(struct bio *bio, int sectors,
>
> bio_advance(bio, split->bi_iter.bi_size);
>
> + bio_clone_blkcg_association(split, bio);
> +
First, I think this should be done inside of bio_clone_fast and
bio_clone_bioset instead of in bio_split. Otherwise you miss other
places where bios are cloned, and I'm guessing that's bad. You could
also then get rid of this code in btrfs/extent_io.c:
#ifdef CONFIG_BLK_CGROUP
/* FIXME, put this into bio_clone_bioset */
if (bio->bi_css)
bio_associate_blkcg(new, bio->bi_css);
#endif
Next, you went to the trouble of propagating the return value from
bio_associate_blkcg, and then it goes unchecked here in the only caller
of your new function. Since bio_associate_blkcg should not fail when
cloning (right?), I'd change bio_clone_blkcg_association to return void
and to WARN_ON a failure return from bio_associate_blkcg.
Cheers,
Jeff
> return split;
> }
> EXPORT_SYMBOL(bio_split);
> @@ -2016,6 +2018,19 @@ 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
> + */
> +int bio_clone_blkcg_association(struct bio *dst, struct bio *src)
> +{
> + if (src->bi_css)
> + return bio_associate_blkcg(dst, src->bi_css);
> +
> + return 0;
> +}
> +
> #endif /* CONFIG_BLK_CGROUP */
>
> static void __init biovec_init_slabs(void)
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index 6b7481f..8535f81 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -527,11 +527,13 @@ 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);
> +int 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) { }
> +int bio_clone_blkcg_association(struct bio *dst, struct bio *src) { return
> 0; }
> #endif /* CONFIG_BLK_CGROUP */
>
> #ifdef CONFIG_HIGHMEM
