netdev - [PATCH bpf-next 10/19] bpf: Disable migration in array_map

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Message-Id: <20250106081900.1665573-11-houtao@huaweicloud.com>
Date: Mon,  6 Jan 2025 16:18:51 +0800
From: Hou Tao <houtao@...weicloud.com>
To: bpf@...r.kernel.org,
	netdev@...r.kernel.org
Cc: Martin KaFai Lau <martin.lau@...ux.dev>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Andrii Nakryiko <andrii@...nel.org>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Hao Luo <haoluo@...gle.com>,
	Yonghong Song <yonghong.song@...ux.dev>,
	Daniel Borkmann <daniel@...earbox.net>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Jiri Olsa <jolsa@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	houtao1@...wei.com,
	xukuohai@...wei.com
Subject: [PATCH bpf-next 10/19] bpf: Disable migration in array_map_free()

From: Hou Tao <houtao1@...wei.com>

When freeing the array map, the destroy procedure may invoke
bpf_obj_free_fields() to free the special fields in map value
(e.g., kptr). Since kptrs may be allocated from bpf memory allocator,
migrate_{disable|enable} pairs are necessary for the freeing of these
kptrs.

To simplify reasoning about when migrate_disable() is needed for the
freeing of these dynamically-allocated kptrs, let the caller to
guarantee migration is disabled before invoking bpf_obj_free_fields().

Therefore, the patch adds migrate_{disable|enable} pair in
array_map_free(). The migrate_{disable|enable} pairs in the underlying
implementation of bpf_obj_free_fields() will be removed by the following
patch.

Signed-off-by: Hou Tao <houtao1@...wei.com>
---
 kernel/bpf/arraymap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index eb28c0f219ee..451737493b17 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -455,6 +455,7 @@ static void array_map_free(struct bpf_map *map)
 	struct bpf_array *array = container_of(map, struct bpf_array, map);
 	int i;
 
+	migrate_disable();
 	if (!IS_ERR_OR_NULL(map->record)) {
 		if (array->map.map_type == BPF_MAP_TYPE_PERCPU_ARRAY) {
 			for (i = 0; i < array->map.max_entries; i++) {
@@ -471,6 +472,7 @@ static void array_map_free(struct bpf_map *map)
 				bpf_obj_free_fields(map->record, array_map_elem_ptr(array, i));
 		}
 	}
+	migrate_enable();
 
 	if (array->map.map_type == BPF_MAP_TYPE_PERCPU_ARRAY)
 		bpf_array_free_percpu(array);
-- 
2.29.2