Re: [PATCH 1/2] io_uring/cmd: let cmds to know about dying task

[Ming Lei <ming.lei@redhat.com>]

On Fri, Nov 1, 2024 at 12:33 AM Mark Harmstone <maharmstone@fb.com> wrote:
>
> From: Pavel Begunkov <asml.silence@gmail.com>
>
> When the taks that submitted a request is dying, a task work for that
> request might get run by a kernel thread or even worse by a half
> dismantled task. We can't just cancel the task work without running the
> callback as the cmd might need to do some clean up, so pass a flag
> instead. If set, it's not safe to access any task resources and the
> callback is expected to cancel the cmd ASAP.
>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  include/linux/io_uring_types.h | 1 +
>  io_uring/uring_cmd.c           | 6 +++++-
>  2 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
> index 4b9ba523978d..2ee5dc105b58 100644
> --- a/include/linux/io_uring_types.h
> +++ b/include/linux/io_uring_types.h
> @@ -37,6 +37,7 @@ enum io_uring_cmd_flags {
>         /* set when uring wants to cancel a previously issued command */
>         IO_URING_F_CANCEL               = (1 << 11),
>         IO_URING_F_COMPAT               = (1 << 12),
> +       IO_URING_F_TASK_DEAD            = (1 << 13),
>  };
>
>  struct io_wq_work_node {
> diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
> index 39c3c816ec78..78a8ba5d39ae 100644
> --- a/io_uring/uring_cmd.c
> +++ b/io_uring/uring_cmd.c
> @@ -119,9 +119,13 @@ EXPORT_SYMBOL_GPL(io_uring_cmd_mark_cancelable);
>  static void io_uring_cmd_work(struct io_kiocb *req, struct io_tw_state *ts)
>  {
>         struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
> +       unsigned int flags = IO_URING_F_COMPLETE_DEFER;
> +
> +       if (req->task != current)
> +               flags |= IO_URING_F_TASK_DEAD;

Looks fine,

Reviewed-by: Ming Lei <ming.lei@redhat.com>

BTW,  uring_cmd can get notified when the ring/task is dying if
io_uring_cmd_mark_cancelable() is called on the command.


Thanks,
Ming