Re: [PATCH v3 5/6] io-wq: warn about future set_task_comm() overflows.

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

On 4/25/21 12:26 AM, Stefan Metzmacher wrote:
> Signed-off-by: Stefan Metzmacher <metze@samba.org>
> ---
>  fs/io-wq.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/io-wq.c b/fs/io-wq.c
> index cd1af924c3d1..b80c5d905127 100644
> --- a/fs/io-wq.c
> +++ b/fs/io-wq.c
> @@ -640,7 +640,19 @@ static void create_io_worker(struct io_wq *wq, struct io_wqe *wqe, int index)
>  		return;
>  	}
>  
> -	snprintf(tsk_comm, sizeof(tsk_comm), "iou-wrk-%d", wq->task->pid);
> +	/*
> +	 * The limit value of pid_max_max/PID_MAX_LIMIT
> +	 * is 4 * 1024 * 1024 = 4194304.
> +	 *
> +	 * TASK_COMM_LEN is 16, so we have 15 chars to fill.
> +	 *
> +	 * With "iou-wrk-4194304" we just fit into 15 chars.
> +	 * If that ever changes we may better add some special
> +	 * handling for PF_IO_WORKER in proc_task_name(), as that
> +	 * allows up to 63 chars.
> +	 */
> +	WARN_ON(snprintf(tsk_comm, sizeof(tsk_comm),
> +			 "iou-wrk-%d", wq->task->pid) >= sizeof(tsk_comm));


We don't really care, so saner would be to just to leave them and don't
warn. Not see much need but can be something like "iou-wrk-00000*" if
overflowed. Same for 6/6.


>  	set_task_comm(tsk, tsk_comm);
>  
>  	tsk->pf_io_worker = worker;
> 

-- 
Pavel Begunkov