Re: [PATCH v1 07/11] io_uring/kbuf: add recycling for kernel managed buffer rings

[Jens Axboe <axboe@kernel.dk>]

On 2/9/26 5:28 PM, Joanne Koong wrote:
> +int io_uring_kmbuf_recycle(struct io_uring_cmd *cmd, unsigned int buf_group,
> +			   u64 addr, unsigned int len, unsigned int bid,
> +			   unsigned int issue_flags)
> +{
> +	struct io_kiocb *req = cmd_to_io_kiocb(cmd);
> +	struct io_ring_ctx *ctx = req->ctx;
> +	struct io_uring_buf_ring *br;
> +	struct io_uring_buf *buf;
> +	struct io_buffer_list *bl;
> +	int ret = -EINVAL;
> +
> +	if (WARN_ON_ONCE(req->flags & REQ_F_BUFFERS_COMMIT))
> +		return ret;
> +
> +	io_ring_submit_lock(ctx, issue_flags);
> +
> +	bl = io_buffer_get_list(ctx, buf_group);
> +
> +	if (!bl || WARN_ON_ONCE(!(bl->flags & IOBL_BUF_RING)) ||
> +	    WARN_ON_ONCE(!(bl->flags & IOBL_KERNEL_MANAGED)))
> +		goto done;
> +
> +	br = bl->buf_ring;
> +
> +	if (WARN_ON_ONCE((br->tail - bl->head) >= bl->nr_entries))
> +		goto done;

I think you want:

	if (WARN_ON_ONCE((__u16)(br->tail - bl->head) >= bl->nr_entries))

here to avoid int promotion from messing this up if tail has wrapped.

In general, across the patches for the WARN_ON_ONCE(), it's not a huge
issue to have a litter of them for now. Hopefully we can prune some of
these down the line, however.

-- 
Jens Axboe