zsmalloc: zs_malloc: return ERR_PTR on failure

zs_malloc returns 0 if it fails.  zs_zpool_malloc will return -1 when
zs_malloc return 0.  But -1 makes the return value unclear.

For example, when zswap_frontswap_store calls zs_malloc through
zs_zpool_malloc, it will return -1 to its caller.  The other return value
is -EINVAL, -ENODEV or something else.

This commit changes zs_malloc to return ERR_PTR on failure.  It didn't
just let zs_zpool_malloc return -ENOMEM becaue zs_malloc has two types of
failure:

- size is not OK return -EINVAL
- memory alloc fail return -ENOMEM.

Link: https://lkml.kernel.org/r/20220714080757.12161-1-teawater@gmail.com
Signed-off-by: Hui Zhu <teawater@antgroup.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/block/zram/zram_drv.c

@@ -1389,9 +1389,9 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 			__GFP_HIGHMEM |
 			__GFP_MOVABLE);
 
-	if (unlikely(!handle)) {
+	if (IS_ERR((void *)handle)) {
 		zcomp_stream_put(zram->comp);
-		return -ENOMEM;
+		return PTR_ERR((void *)handle);
 	}
 
 	alloced_pages = zs_get_total_pages(zram->mem_pool);

mm/zsmalloc.c

@@ -399,7 +399,10 @@ static int zs_zpool_malloc(void *pool, size_t size, gfp_t gfp,
 			unsigned long *handle)
 {
 	*handle = zs_malloc(pool, size, gfp);
-	return *handle ? 0 : -1;
+
+	if (IS_ERR((void *)(*handle)))
+		return PTR_ERR((void *)*handle);
+	return 0;
 }
 static void zs_zpool_free(void *pool, unsigned long handle)
 {
@@ -1400,7 +1403,7 @@ static unsigned long obj_malloc(struct zs_pool *pool,
  * @gfp: gfp flags when allocating object
  *
  * On success, handle to the allocated object is returned,
- * otherwise 0.
+ * otherwise an ERR_PTR().
  * Allocation requests with size > ZS_MAX_ALLOC_SIZE will fail.
  */
 unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp)
@@ -1411,11 +1414,11 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp)
 	struct zspage *zspage;
 
 	if (unlikely(!size || size > ZS_MAX_ALLOC_SIZE))
-		return 0;
+		return (unsigned long)ERR_PTR(-EINVAL);
 
 	handle = cache_alloc_handle(pool, gfp);
 	if (!handle)
-		return 0;
+		return (unsigned long)ERR_PTR(-ENOMEM);
 
 	/* extra space in chunk to keep the handle */
 	size += ZS_HANDLE_SIZE;
@@ -1440,7 +1443,7 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp)
 	zspage = alloc_zspage(pool, class, gfp);
 	if (!zspage) {
 		cache_free_handle(pool, handle);
-		return 0;
+		return (unsigned long)ERR_PTR(-ENOMEM);
 	}
 
 	spin_lock(&class->lock);