bpf: Simplify code of destroy_mem_alloc() with kmemdup().

Use kmemdup() to simplify the code.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/bpf/20230706033447.54696-3-alexei.starovoitov@gmail.com

kernel/bpf/memalloc.c

@@ -499,7 +499,7 @@ static void destroy_mem_alloc(struct bpf_mem_alloc *ma, int rcu_in_progress)
 		return;
 	}
 
-	copy = kmalloc(sizeof(*ma), GFP_KERNEL);
+	copy = kmemdup(ma, sizeof(*ma), GFP_KERNEL);
 	if (!copy) {
 		/* Slow path with inline barrier-s */
 		free_mem_alloc(ma);
@@ -507,10 +507,7 @@ static void destroy_mem_alloc(struct bpf_mem_alloc *ma, int rcu_in_progress)
 	}
 
 	/* Defer barriers into worker to let the rest of map memory to be freed */
-	copy->cache = ma->cache;
-	ma->cache = NULL;
-	copy->caches = ma->caches;
-	ma->caches = NULL;
+	memset(ma, 0, sizeof(*ma));
 	INIT_WORK(&copy->work, free_mem_alloc_deferred);
 	queue_work(system_unbound_wq, &copy->work);
 }