From c42b8c4ada164fb12f7633aac9d5774ceba2b2ef Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Fri, 13 Apr 2018 16:25:57 -0600 Subject: [PATCH] loop: handle short DIO reads 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 --- 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 28ec10abec9e..1a6fbecd8a00 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) -- 2.25.1