Re: [PATCH 2/2] nvmet: fix a race condition between release_queue and io_work

[Maurizio Lombardi <mlombard@redhat.com>]

On Mon, Nov 15, 2021 at 11:48:38AM +0200, Sagi Grimberg wrote:
> I see, the reason why we hit this is because we uninit_data_in_cmds as
> we need to clear the the sq references so nvmet_sq_destroy() can
> complete, and then when nvmet_sq_destroy schedules io_work we hit this.
> 
> I think what we need is to make sure we don't recv from the socket.
> How about this patch:
> --
> diff --git a/drivers/nvme/target/tcp.c b/drivers/nvme/target/tcp.c
> index 6eb0b3153477..65210dec3f1a 100644
> --- a/drivers/nvme/target/tcp.c
> +++ b/drivers/nvme/target/tcp.c
> @@ -1436,6 +1436,8 @@ static void nvmet_tcp_release_queue_work(struct
> work_struct *w)
>         mutex_unlock(&nvmet_tcp_queue_mutex);
> 
>         nvmet_tcp_restore_socket_callbacks(queue);
> +       /* stop accepting incoming data */
> +       queue->rcv_state = NVMET_TCP_RECV_ERR;
>         flush_work(&queue->io_work);
> 
>         nvmet_tcp_uninit_data_in_cmds(queue);
> --
> 

Ok I can repeat the test, but you probably want to do this instead:

diff --git a/drivers/nvme/target/tcp.c b/drivers/nvme/target/tcp.c
index fb72e2d67fd5..d21b525fd4cb 100644
--- a/drivers/nvme/target/tcp.c
+++ b/drivers/nvme/target/tcp.c
@@ -1450,7 +1450,9 @@ static void nvmet_tcp_release_queue_work(struct work_struct *w)
        mutex_unlock(&nvmet_tcp_queue_mutex);
 
        nvmet_tcp_restore_socket_callbacks(queue);
-       flush_work(&queue->io_work);
+       cancel_work_sync(&queue->io_work);
+       /* stop accepting incoming data */
+       queue->rcv_state = NVMET_TCP_RECV_ERR;
 
        nvmet_tcp_uninit_data_in_cmds(queue);
        nvmet_sq_destroy(&queue->nvme_sq);

If you don't perform a cancel_work_sync() you may race against a running
io_work thread that may overwrite rcv_state with some other value.

Maurizio