netdev - [PATCH bpf-next] bpf: no longer acquire map_idr_lock in bpf_map_inc_not

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Message-ID: <20250301191315.1532629-1-edumazet@google.com>
Date: Sat,  1 Mar 2025 19:13:15 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	John Fastabend <john.fastabend@...il.com>
Cc: Stanislav Fomichev <sdf@...ichev.me>, netdev@...r.kernel.org, bpf@...r.kernel.org, 
	eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>, 
	Kui-Feng Lee <kuifeng@...a.com>, Martin KaFai Lau <martin.lau@...nel.org>
Subject: [PATCH bpf-next] bpf: no longer acquire map_idr_lock in bpf_map_inc_not_zero()

bpf_sk_storage_clone() is the only caller of bpf_map_inc_not_zero()
and is holding rcu_read_lock().

map_idr_lock does not add any protection, just remove the cost
for passive TCP flows.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Kui-Feng Lee <kuifeng@...a.com>
Cc: Martin KaFai Lau <martin.lau@...nel.org>
---
 kernel/bpf/syscall.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index e1e42e918ba7f682223e9a78028bb0cc360c01ce..d68c8d61f7ceddb732a5646c00b8f0c71fdc2d71 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1593,11 +1593,8 @@ struct bpf_map *__bpf_map_inc_not_zero(struct bpf_map *map, bool uref)
 
 struct bpf_map *bpf_map_inc_not_zero(struct bpf_map *map)
 {
-	spin_lock_bh(&map_idr_lock);
-	map = __bpf_map_inc_not_zero(map, false);
-	spin_unlock_bh(&map_idr_lock);
-
-	return map;
+	lockdep_assert(rcu_read_lock_held());
+	return __bpf_map_inc_not_zero(map, false);
 }
 EXPORT_SYMBOL_GPL(bpf_map_inc_not_zero);
 
-- 
2.48.1.711.g2feabab25a-goog