Re: [PATCH RFC v4 12/15] io_uring/cmd: let cmds to know about dying task

[Pavel Begunkov <asml.silence@gmail.com>]

On 10/16/24 01:05, Bernd Schubert 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 7abdc09271245ff7de3fb9a905ca78b7561e37eb..869a81c63e4970576155043fce7fe656293d7f58 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 21ac5fb2d5f087e1174d5c94815d580972db6e3f..82c6001cc0696bbcbebb92153e1461f2a9aeebc3 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;

Bernd, please don't change patches under my name without any
notice. This check is wrong, just stick to the original

https://lore.kernel.org/io-uring/d2528a1c-3d7c-4124-953c-02e8e415529e@gmail.com/

In general if you need to change something, either stick your
name, so that I know it might be a derivative, or reflect it in
the commit message, e.g.

Signed-off-by: initial author
[Person 2: changed this and that]
Signed-off-by: person 2

Also, a quick note that btrfs also need the patch, so it'll likely
get queued via either io_uring or btrfs trees for next.

>   	/* task_work executor checks the deffered list completion */
> -	ioucmd->task_work_cb(ioucmd, IO_URING_F_COMPLETE_DEFER);
> +	ioucmd->task_work_cb(ioucmd, flags);
>   }
>   
>   void __io_uring_cmd_do_in_task(struct io_uring_cmd *ioucmd,
> 

-- 
Pavel Begunkov