On Tue, Sep 14, 2021 at 11:11:06AM +0800, yukuai (C) wrote: > On 2021/09/14 9:11, Ming Lei wrote: > > On Thu, Sep 09, 2021 at 10:12:55PM +0800, Yu Kuai wrote: > > > blk_mq_tag_to_rq() can only ensure to return valid request in > > > following situation: > > > > > > 1) client send request message to server first > > > submit_bio > > > ... > > > blk_mq_get_tag > > > ... > > > blk_mq_get_driver_tag > > > ... > > > nbd_queue_rq > > > nbd_handle_cmd > > > nbd_send_cmd > > > > > > 2) client receive respond message from server > > > recv_work > > > nbd_read_stat > > > blk_mq_tag_to_rq > > > > > > If step 1) is missing, blk_mq_tag_to_rq() will return a stale > > > request, which might be freed. Thus convert to use > > > blk_mq_find_and_get_req() to make sure the returned request is not > > > freed. > > > > But NBD_CMD_INFLIGHT has been added for checking if the reply is > > expected, do we still need blk_mq_find_and_get_req() for covering > > this issue? BTW, request and its payload is pre-allocated, so there > > isn't real use-after-free. > > Hi, Ming > > Checking NBD_CMD_INFLIGHT relied on the request founded by tag is valid, > not the other way round. > > nbd_read_stat > req = blk_mq_tag_to_rq() > cmd = blk_mq_rq_to_pdu(req) > mutex_lock(cmd->lock) > checking NBD_CMD_INFLIGHT Request and its payload is pre-allocated, and either req->ref or cmd->lock can serve the same purpose here. Once cmd->lock is held, you can check if the cmd is inflight or not. If it isn't inflight, just return -ENOENT. Is there any problem to handle in this way? Thanks, Ming
