Re: [PATCH 1/3] io_uring: simplify io_mem_alloc return values

[Gabriel Krisman Bertazi <krisman@suse.de>]

Pavel Begunkov <asml.silence@gmail.com> writes:

> io_mem_alloc() returns a pointer on success and a pointer-encoded error
> otherwise. However, it can only fail with -ENOMEM, just return NULL on
> failure. PTR_ERR is usually pretty error prone.
>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  io_uring/io_uring.c | 14 +++++---------
>  io_uring/kbuf.c     |  4 ++--
>  2 files changed, 7 insertions(+), 11 deletions(-)
>
> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> index e7d7a456b489..1d0eac0cc8aa 100644
> --- a/io_uring/io_uring.c
> +++ b/io_uring/io_uring.c
> @@ -2802,12 +2802,8 @@ static void io_rings_free(struct io_ring_ctx *ctx)
>  void *io_mem_alloc(size_t size)
>  {
>  	gfp_t gfp = GFP_KERNEL_ACCOUNT | __GFP_ZERO | __GFP_NOWARN | __GFP_COMP;
> -	void *ret;
>  
> -	ret = (void *) __get_free_pages(gfp, get_order(size));
> -	if (ret)
> -		return ret;
> -	return ERR_PTR(-ENOMEM);
> +	return (void *) __get_free_pages(gfp, get_order(size));
>  }
>  
>  static unsigned long rings_size(struct io_ring_ctx *ctx, unsigned int sq_entries,
> @@ -3762,8 +3758,8 @@ static __cold int io_allocate_scq_urings(struct io_ring_ctx *ctx,
>  	else
>  		rings = io_rings_map(ctx, p->cq_off.user_addr, size);
>  
> -	if (IS_ERR(rings))
> -		return PTR_ERR(rings);
> +	if (!rings)
> +		return -ENOMEM;
>

Sorry, I started reviewing this, got excited about the error path quick
fix, and didn't finish the review before it got it.

I think this change is broken for the ctx->flags & IORING_SETUP_NO_MMAP
case, because io_rings_map returns ERR_PTR, and not NULL.  In addition,
io_rings_map might fail for multiple reasons, and we want to propagate
the different error codes up here.

-- 
Gabriel Krisman Bertazi