Re: [PATCH v3 5/5] io_uring/rsrc: add io_uring_registered_mem_region_get()

[Jens Axboe <axboe@kernel.dk>]

On 3/24/26 4:14 PM, Joanne Koong wrote:
> diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
> index cf5638406a0c..c706324fd66d 100644
> --- a/io_uring/rsrc.c
> +++ b/io_uring/rsrc.c
> @@ -1182,6 +1182,24 @@ int io_import_reg_buf(struct io_kiocb *req, struct iov_iter *iter,
>  	return io_import_fixed(ddir, iter, node->buf, buf_addr, len);
>  }
>  
> +void *io_uring_registered_mem_region_get(struct io_uring_cmd *cmd,
> +					 unsigned *nr_pages,
> +					 unsigned issue_flags)
> +{
> +	struct io_ring_ctx *ctx = cmd_to_io_kiocb(cmd)->ctx;
> +	void *ptr;
> +
> +	io_ring_submit_lock(ctx, issue_flags);
> +
> +	ptr = ctx->param_region.ptr;
> +	*nr_pages = ctx->param_region.nr_pages;
> +
> +	io_ring_submit_unlock(ctx, issue_flags);
> +
> +	return ptr;
> +}
> +EXPORT_SYMBOL_GPL(io_uring_registered_mem_region_get);

This looks suspicious, but I actually think it looks suspicious because
you add the submit locking around it. For patterns like that, it makes
the brain go "hmm, what protects this from going invalid the instant
io_ring_submit_unlock() is called??". But this should be stable for the
duration of the ring, hence the locking should not be needed at all?

I'd probably also prefer wrapping this in some kind of return struct, so
that you just return that rather than having one part returned directly
and one stuffed in a pointer to an unsigned for number of pages.

-- 
Jens Axboe