Hello Long,
On Thu, Jun 03, 2021 at 03:34:31PM -0700, longli@xxxxxxxxxxxxxxxxx wrote:
> From: Long Li <longli@xxxxxxxxxxxxx>
>
> After commit 07173c3ec276 ("block: enable multipage bvecs"), a bvec can
> have multiple pages. But bio_will_gap() still assumes one page bvec while
> checking for merging. This causes data corruption on drivers relying on
> the correct merging on virt_boundary_mask.
Can you explain the data corruption a bit?
IMO, either single page bvec or multipage bvec should be fine, because
bio_will_gap() just checks if the last bvec of prev bio and the 1st bvec
of next bio can be merged.
>
> Fix this by returning the multi-page bvec for testing gaps for merging.
>
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> Cc: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
> Cc: Pavel Begunkov <asml.silence@xxxxxxxxx>
> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
> Cc: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 07173c3ec276 ("block: enable multipage bvecs")
> Signed-off-by: Long Li <longli@xxxxxxxxxxxxx>
> ---
> include/linux/bio.h | 11 ++++-------
> 1 file changed, 4 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index a0b4cfdf62a4..6b2f609ccfbf 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -44,9 +44,6 @@ static inline unsigned int bio_max_segs(unsigned int nr_segs)
> #define bio_offset(bio) bio_iter_offset((bio), (bio)->bi_iter)
> #define bio_iovec(bio) bio_iter_iovec((bio), (bio)->bi_iter)
>
> -#define bio_multiple_segments(bio) \
> - ((bio)->bi_iter.bi_size != bio_iovec(bio).bv_len)
> -
> #define bvec_iter_sectors(iter) ((iter).bi_size >> 9)
> #define bvec_iter_end_sector(iter) ((iter).bi_sector + bvec_iter_sectors((iter)))
>
> @@ -271,7 +268,7 @@ static inline void bio_clear_flag(struct bio *bio, unsigned int bit)
>
> static inline void bio_get_first_bvec(struct bio *bio, struct bio_vec *bv)
> {
> - *bv = bio_iovec(bio);
> + *bv = mp_bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
> }
>
> static inline void bio_get_last_bvec(struct bio *bio, struct bio_vec *bv)
> @@ -279,10 +276,10 @@ static inline void bio_get_last_bvec(struct bio *bio, struct bio_vec *bv)
> struct bvec_iter iter = bio->bi_iter;
> int idx;
>
> - if (unlikely(!bio_multiple_segments(bio))) {
> - *bv = bio_iovec(bio);
> + /* this bio has only one bvec */
> + *bv = mp_bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
> + if (bv->bv_len == bio->bi_iter.bi_size)
> return;
> - }
>
> bio_advance_iter(bio, &iter, iter.bi_size);
The patch itself looks fine, given both bio_get_first_bvec() and bio_get_last_bvec()
are used in bio_will_gap() only.
Thanks,
Ming
