netdev - [PATCH bpf-next 03/19] bpf: Remove migrate_{disable|enable} in htab_elem

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Message-Id: <20250106081900.1665573-4-houtao@huaweicloud.com>
Date: Mon,  6 Jan 2025 16:18:44 +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 03/19] bpf: Remove migrate_{disable|enable} in htab_elem_free

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

htab_elem_free() has two call-sites: delete_all_elements() has already
disabled migration, free_htab_elem() is invoked by other 4 functions:
__htab_map_lookup_and_delete_elem, __htab_map_lookup_and_delete_batch,
htab_map_update_elem and htab_map_delete_elem.

BPF syscall has already disabled migration before invoking
->map_update_elem, ->map_delete_elem, and ->map_lookup_and_delete_elem
callbacks for hash map. __htab_map_lookup_and_delete_batch() also
disables migration before invoking free_htab_elem(). ->map_update_elem()
and ->map_delete_elem() of hash map may be invoked by BPF program and
the running context of BPF program has already disabled migration.
Therefore, it is safe to remove the migration_{disable|enable} pair in
htab_elem_free()

Signed-off-by: Hou Tao <houtao1@...wei.com>
---
 kernel/bpf/hashtab.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 42af7fac61b9..1db71d25836e 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -895,13 +895,13 @@ static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
 
 static void htab_elem_free(struct bpf_htab *htab, struct htab_elem *l)
 {
+	cant_migrate();
+
 	check_and_free_fields(htab, l);
 
-	migrate_disable();
 	if (htab->map.map_type == BPF_MAP_TYPE_PERCPU_HASH)
 		bpf_mem_cache_free(&htab->pcpu_ma, l->ptr_to_pptr);
 	bpf_mem_cache_free(&htab->ma, l);
-	migrate_enable();
 }
 
 static void htab_put_fd_value(struct bpf_htab *htab, struct htab_elem *l)
-- 
2.29.2