commit 22b106e5355d6e7a9c3b5cb5ed4ef22ae585ea94 upstream.

Commit d92c370a16cb ("block: really clone the block cgroup in bio_clone_blkg_association") changed bio_clone_blkg_association() to just clone bio->bi_blkg reference from source to destination bio. This is however wrong if the source and destination bios are against different block devices because struct blkcg_gq is different for each bdev-blkcg pair. This will result in IOs being accounted (and throttled as a result) multiple times against the same device (src bdev) while throttling of the other device (dst bdev) is ignored. In case of BFQ the inconsistency can even result in crashes in bfq_bic_update_cgroup(). Fix the problem by looking up correct blkcg_gq for the cloned bio.

Reported-by: Logan Gunthorpe logang@deltatee.com Reported-and-tested-by: Donald Buczek buczek@molgen.mpg.de Fixes: d92c370a16cb ("block: really clone the block cgroup in bio_clone_blkg_association") CC: stable@vger.kernel.org Reviewed-by: Christoph Hellwig hch@lst.de Signed-off-by: Jan Kara jack@suse.cz Link: https://lore.kernel.org/r/20220602081242.7731-1-jack@suse.cz Signed-off-by: Jens Axboe axboe@kernel.dk --- block/blk-cgroup.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)

This patch should be a backport for 5.15, 5.17, and 5.18 stable branches.

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 07a2524e6efd..ce5858dadca5 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1886,12 +1886,8 @@ EXPORT_SYMBOL_GPL(bio_associate_blkg); */ void bio_clone_blkg_association(struct bio *dst, struct bio *src) { - if (src->bi_blkg) { - if (dst->bi_blkg) - blkg_put(dst->bi_blkg); - blkg_get(src->bi_blkg); - dst->bi_blkg = src->bi_blkg; - } + if (src->bi_blkg) + bio_associate_blkg_from_css(dst, &bio_blkcg(src)->css); } EXPORT_SYMBOL_GPL(bio_clone_blkg_association);