On Fri, Apr 13, 2018 at 04:30:36PM -0600, Jens Axboe wrote:
> We ran into an issue with loop and btrfs, where btrfs would complain about
> checksum errors. It turns out that is because we don't handle short reads
> at all, we just zero fill the remainder. Worse than that, we don't handle
> the filling properly, which results in loop trying to advance a single
> bio by much more than its size, since it doesn't take chaining into
> account.
>
> Handle short reads appropriately, by simply retrying at the new correct
> offset. End the remainder of the request with EIO, if we get a 0 read.
>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> ---
> drivers/block/loop.c | 34 +++++++++++++++++++++++++++-------
> 1 file changed, 27 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 8b2fde2109fc..5d4e31655d96 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -451,16 +451,36 @@ static int lo_req_flush(struct loop_device *lo, struct request *rq)
> static void lo_complete_rq(struct request *rq)
> {
> struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq);
> + blk_status_t ret = BLK_STS_OK;
>
> - if (unlikely(req_op(rq) == REQ_OP_READ && cmd->use_aio &&
> - cmd->ret >= 0 && cmd->ret < blk_rq_bytes(rq))) {
> - struct bio *bio = rq->bio;
> -
> - bio_advance(bio, cmd->ret);
> - zero_fill_bio(bio);
> + if (!cmd->use_aio || cmd->ret < 0 || cmd->ret == blk_rq_bytes(rq) ||
> + req_op(rq) != REQ_OP_READ) {
> + if (cmd->ret < 0)
> + ret = BLK_STS_IOERR;
> + goto end_io;
> }
>
> - blk_mq_end_request(rq, cmd->ret < 0 ? BLK_STS_IOERR : BLK_STS_OK);
> + /*
> + * Short READ - if we got some data, advance our request and
> + * retry it. If we got no data, end the rest with EIO.
> + */
> + if (cmd->ret) {
> + blk_update_request(rq, BLK_STS_OK, cmd->ret);
> + cmd->ret = 0;
> + blk_mq_requeue_request(rq, true);
> + } else {
> + if (cmd->use_aio) {
> + struct bio *bio = rq->bio;
> +
> + while (bio) {
> + zero_fill_bio(bio);
> + bio = bio->bi_next;
> + }
> + }
> + ret = BLK_STS_IOERR;
> +end_io:
> + blk_mq_end_request(rq, ret);
> + }
> }
>
> static void lo_rw_aio_do_completion(struct loop_cmd *cmd)
> --
> 2.7.4
>
Looks fine, short read will be guaranteed to complete when zero read
is triggered.
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
--
Ming
