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    Subject[patch v8 1/7] nbd: don't handle response without a corresponding request message
    Date
    While handling a response message from server, nbd_read_stat() will
    try to get request by tag, and then complete the request. However,
    this is problematic if nbd haven't sent a corresponding request
    message:

    t1 t2
    submit_bio
    nbd_queue_rq
    blk_mq_start_request
    recv_work
    nbd_read_stat
    blk_mq_tag_to_rq
    blk_mq_complete_request
    nbd_send_cmd

    Thus add a new cmd flag 'NBD_CMD_INFLIGHT', it will be set in
    nbd_send_cmd() and checked in nbd_read_stat().

    Noted that this patch can't fix that blk_mq_tag_to_rq() might
    return a freed request, and this will be fixed in following
    patches.

    Signed-off-by: Yu Kuai <yukuai3@huawei.com>
    Reviewed-by: Ming Lei <ming.lei@redhat.com>
    ---
    drivers/block/nbd.c | 22 +++++++++++++++++++++-
    1 file changed, 21 insertions(+), 1 deletion(-)

    diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
    index 5170a630778d..23ded569e8d3 100644
    --- a/drivers/block/nbd.c
    +++ b/drivers/block/nbd.c
    @@ -126,6 +126,12 @@ struct nbd_device {
    };

    #define NBD_CMD_REQUEUED 1
    +/*
    + * This flag will be set if nbd_queue_rq() succeed, and will be checked and
    + * cleared in completion. Both setting and clearing of the flag are protected
    + * by cmd->lock.
    + */
    +#define NBD_CMD_INFLIGHT 2

    struct nbd_cmd {
    struct nbd_device *nbd;
    @@ -400,6 +406,7 @@ static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req,
    if (!mutex_trylock(&cmd->lock))
    return BLK_EH_RESET_TIMER;

    + __clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);
    if (!refcount_inc_not_zero(&nbd->config_refs)) {
    cmd->status = BLK_STS_TIMEOUT;
    mutex_unlock(&cmd->lock);
    @@ -729,6 +736,12 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
    cmd = blk_mq_rq_to_pdu(req);

    mutex_lock(&cmd->lock);
    + if (!__test_and_clear_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
    + dev_err(disk_to_dev(nbd->disk), "Suspicious reply %d (status %u flags %lu)",
    + tag, cmd->status, cmd->flags);
    + ret = -ENOENT;
    + goto out;
    + }
    if (cmd->cmd_cookie != nbd_handle_to_cookie(handle)) {
    dev_err(disk_to_dev(nbd->disk), "Double reply on req %p, cmd_cookie %u, handle cookie %u\n",
    req, cmd->cmd_cookie, nbd_handle_to_cookie(handle));
    @@ -828,6 +841,7 @@ static bool nbd_clear_req(struct request *req, void *data, bool reserved)
    return true;

    mutex_lock(&cmd->lock);
    + __clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);
    cmd->status = BLK_STS_IOERR;
    mutex_unlock(&cmd->lock);

    @@ -964,7 +978,13 @@ static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)
    * returns EAGAIN can be retried on a different socket.
    */
    ret = nbd_send_cmd(nbd, cmd, index);
    - if (ret == -EAGAIN) {
    + /*
    + * Access to this flag is protected by cmd->lock, thus it's safe to set
    + * the flag after nbd_send_cmd() succeed to send request to server.
    + */
    + if (!ret)
    + __set_bit(NBD_CMD_INFLIGHT, &cmd->flags);
    + else if (ret == -EAGAIN) {
    dev_err_ratelimited(disk_to_dev(nbd->disk),
    "Request send failed, requeueing\n");
    nbd_mark_nsock_dead(nbd, nsock, 1);
    --
    2.31.1
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