zsmalloc: zs_destroy_pool: add size_class NULL check

Inside the zs_destroy_pool() function, there can still be NULL size_class
pointers: if when the next size_class is allocated, inside
zs_create_pool() function, kzalloc will return NULL and handling the error
condition, zs_create_pool() will call zs_destroy_pool().

Link: https://lkml.kernel.org/r/[email protected]
Fixes: f24263a ("zsmalloc: remove unnecessary size_class NULL check")
Signed-off-by: Alexey Romanov <[email protected]>
Reviewed-by: Sergey Senozhatsky <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Nitin Gupta <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: mRrvz

mm/zsmalloc.c

@@ -2311,6 +2311,9 @@ void zs_destroy_pool(struct zs_pool *pool)
 		int fg;
 		struct size_class *class = pool->size_class[i];
 
+		if (!class)
+			continue;
+
 		if (class->index != i)
 			continue;