netdev - [PATCH bpf-next 09/19] bpf: Disable migration in bpf_selem_free

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Message-Id: <20250106081900.1665573-10-houtao@huaweicloud.com>
Date: Mon,  6 Jan 2025 16:18:50 +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 09/19] bpf: Disable migration in bpf_selem_free_rcu

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

bpf_selem_free_rcu() calls 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
bpf_selem_free_rcu(). 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/bpf_local_storage.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
index e94820f6b0cd..615a3034baeb 100644
--- a/kernel/bpf/bpf_local_storage.c
+++ b/kernel/bpf/bpf_local_storage.c
@@ -217,7 +217,10 @@ static void bpf_selem_free_rcu(struct rcu_head *rcu)
 	selem = container_of(rcu, struct bpf_local_storage_elem, rcu);
 	/* The bpf_local_storage_map_free will wait for rcu_barrier */
 	smap = rcu_dereference_check(SDATA(selem)->smap, 1);
+
+	migrate_disable();
 	bpf_obj_free_fields(smap->map.record, SDATA(selem)->data);
+	migrate_enable();
 	bpf_mem_cache_raw_free(selem);
 }
 
-- 
2.29.2