Re: [PATCH 1/4] io_uring/uring_cmd: get rid of using req->imu

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

On Mon, Oct 21, 2024 at 08:03:20PM -0600, Jens Axboe wrote:
> It's pretty pointless to use io_kiocb as intermediate storage for this,
> so split the validity check and the actual usage. The resource node is
> assigned upfront at prep time, to prevent it from going away. The actual
> import is never called with the ctx->uring_lock held, so grab it for
> the import.
> 
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
>  io_uring/uring_cmd.c | 22 +++++++++++++++++-----
>  1 file changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
> index 39c3c816ec78..313e2a389174 100644
> --- a/io_uring/uring_cmd.c
> +++ b/io_uring/uring_cmd.c
> @@ -211,11 +211,15 @@ int io_uring_cmd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>  		struct io_ring_ctx *ctx = req->ctx;
>  		u16 index;
>  
> -		req->buf_index = READ_ONCE(sqe->buf_index);
> -		if (unlikely(req->buf_index >= ctx->nr_user_bufs))
> +		index = READ_ONCE(sqe->buf_index);
> +		if (unlikely(index >= ctx->nr_user_bufs))
>  			return -EFAULT;
> -		index = array_index_nospec(req->buf_index, ctx->nr_user_bufs);
> -		req->imu = ctx->user_bufs[index];
> +		req->buf_index = array_index_nospec(index, ctx->nr_user_bufs);
> +		/*
> +		 * Pi node upfront, prior to io_uring_cmd_import_fixed()
> +		 * being called. This prevents destruction of the mapped buffer
> +		 * we'll need at actual import time.
> +		 */
>  		io_req_set_rsrc_node(req, ctx, 0);
>  	}
>  	ioucmd->cmd_op = READ_ONCE(sqe->cmd_op);
> @@ -272,8 +276,16 @@ int io_uring_cmd_import_fixed(u64 ubuf, unsigned long len, int rw,
>  			      struct iov_iter *iter, void *ioucmd)
>  {
>  	struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
> +	struct io_ring_ctx *ctx = req->ctx;
> +	struct io_mapped_ubuf *imu;
> +	int ret;
>  
> -	return io_import_fixed(rw, iter, req->imu, ubuf, len);
> +	mutex_lock(&ctx->uring_lock);
> +	imu = ctx->user_bufs[req->buf_index];
> +	ret = io_import_fixed(rw, iter, imu, ubuf, len);
> +	mutex_unlock(&ctx->uring_lock);

io_uring_cmd_import_fixed is called in nvme ->issue(), and ->uring_lock
may be held already.



thanks,
Ming