On Fri, Jun 04, 2021 at 04:37:19PM -0700, longli@linuxonhyperv.com wrote:
From: Long Li longli@microsoft.com
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 axboe@kernel.dk Cc: Johannes Thumshirn johannes.thumshirn@wdc.com Cc: Pavel Begunkov asml.silence@gmail.com Cc: Ming Lei ming.lei@redhat.com Cc: Tejun Heo tj@kernel.org Cc: "Matthew Wilcox (Oracle)" willy@infradead.org Cc: Jeffle Xu jefflexu@linux.alibaba.com Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Fixes: 07173c3ec276 ("block: enable multipage bvecs") Signed-off-by: Long Li longli@microsoft.com
Change from v1: add commit details on how data corruption happens
Reviewed-by: Ming Lei ming.lei@redhat.com