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 The checking doesn't have any effect on blk_mq_tag_to_rq(). Thanks, Kuai
