io_uring: return error pointer from io_mem_alloc()

In preparation for having more than one time of ring allocator, make the
existing one return valid/error-pointer rather than just NULL.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/io_uring.c

@@ -2691,8 +2691,12 @@ static void io_mem_free(void *ptr)
 static void *io_mem_alloc(size_t size)
 {
 	gfp_t gfp = GFP_KERNEL_ACCOUNT | __GFP_ZERO | __GFP_NOWARN | __GFP_COMP;
+	void *ret;
 
-	return (void *) __get_free_pages(gfp, get_order(size));
+	ret = (void *) __get_free_pages(gfp, get_order(size));
+	if (ret)
+		return ret;
+	return ERR_PTR(-ENOMEM);
 }
 
 static unsigned long rings_size(struct io_ring_ctx *ctx, unsigned int sq_entries,
@@ -3652,6 +3656,7 @@ static __cold int io_allocate_scq_urings(struct io_ring_ctx *ctx,
 {
 	struct io_rings *rings;
 	size_t size, sq_array_offset;
+	void *ptr;
 
 	/* make sure these are sane, as we already accounted them */
 	ctx->sq_entries = p->sq_entries;
@@ -3662,8 +3667,8 @@ static __cold int io_allocate_scq_urings(struct io_ring_ctx *ctx,
 		return -EOVERFLOW;
 
 	rings = io_mem_alloc(size);
-	if (!rings)
-		return -ENOMEM;
+	if (IS_ERR(rings))
+		return PTR_ERR(rings);
 
 	ctx->rings = rings;
 	ctx->sq_array = (u32 *)((char *)rings + sq_array_offset);
@@ -3682,13 +3687,14 @@ static __cold int io_allocate_scq_urings(struct io_ring_ctx *ctx,
 		return -EOVERFLOW;
 	}
 
-	ctx->sq_sqes = io_mem_alloc(size);
-	if (!ctx->sq_sqes) {
+	ptr = io_mem_alloc(size);
+	if (IS_ERR(ptr)) {
 		io_mem_free(ctx->rings);
 		ctx->rings = NULL;
-		return -ENOMEM;
+		return PTR_ERR(ptr);
 	}
 
+	ctx->sq_sqes = ptr;
 	return 0;
 }