Messages in this thread | | | Subject | Re: [PATCH v5 5/6] nbd: convert to use blk_mq_find_and_get_req() | From | "yukuai (C)" <> | Date | Tue, 14 Sep 2021 11:11:06 +0800 |
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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
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