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. If the pages in the bvec go across the
seg_boundary_mask, this check for merging can potentially succeed if only
the 1st page is tested, and can fail if all the pages are tested.
Later, when SCSI builds the SG list the same check for merging is done in
__blk_segment_map_sg_merge() with all the pages in the bvec tested. This
time the check may fail if the pages in bvec go across the
seg_boundary_mask (but tested okay in bio_will_gap() earlier, so those
BIOs were merged). If this check fails, we end up with a broken SG list
for drivers assuming the SG list not having offsets in intermediate pages.
This results in incorrect pages written to the disk.
Fix this by returning the multi-page bvec when testing gaps for merging.
Cc: Jens Axboe <email address hidden>
Cc: Johannes Thumshirn <email address hidden>
Cc: Pavel Begunkov <email address hidden>
Cc: Ming Lei <email address hidden>
Cc: Tejun Heo <email address hidden>
Cc: "Matthew Wilcox (Oracle)" <email address hidden>
Cc: Jeffle Xu <email address hidden>
Cc: <email address hidden>
Cc: <email address hidden>
Fixes: 07173c3ec276 ("block: enable multipage bvecs")
Signed-off-by: Long Li <email address hidden>
Reviewed-by: Ming Lei <email address hidden>
Reviewed-by: Christoph Hellwig <email address hidden>
Link: https://<email address hidden>
Signed-off-by: Jens Axboe <email address hidden>
(cherry picked from commit c9c9762d4d44dcb1b2ba90cfb4122dc11ceebf31 linux-next)
Signed-off-by: Tim Gardner <email address hidden>
Acked-by: Stefan Bader <email address hidden>
Acked-by: Kelsey Skunberg <email address hidden>
Signed-off-by: Tim Gardner <email address hidden>
