Re: [PATCH] block: fix bio_clone_blkg_association() to associate with proper blkcg_gq

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Jun 08, 2022 at 01:45:28PM +0200, Jan Kara wrote:
> 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.

Now queued up, thanks.

greg k-h