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Date: Thu, 18 May 2023 07:47:32 -0700
From: "Paul E. McKenney" <paulmck@kernel.org>
To: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>, Song Liu <song@kernel.org>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>, Stanislav Fomichev <sdf@google.com>,
	Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
	bpf@vger.kernel.org, netdev@vger.kernel.org
Subject: [PATCH bpf] Use call_rcu_hurry() with synchronize_rcu_mult()
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The bpf_struct_ops_map_free() function must wait for both an RCU grace
period and an RCU Tasks grace period, and so it passes call_rcu() and
call_rcu_tasks() to synchronize_rcu_mult().  This works, but on ChromeOS
and Android platforms call_rcu() can have lazy semantics, resulting in
multi-second delays between call_rcu() invocation and invocation of the
corresponding callback.

Therefore, substitute call_rcu_hurry() for call_rcu().

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Yonghong Song <yhs@fb.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Stanislav Fomichev <sdf@google.com>
Cc: Hao Luo <haoluo@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: <bpf@vger.kernel.org>
Cc: <netdev@vger.kernel.org>

diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index d3f0a4825fa6..bacffd6cae60 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -634,7 +634,7 @@ static void bpf_struct_ops_map_free(struct bpf_map *map)
 	 * in the tramopline image to finish before releasing
 	 * the trampoline image.
 	 */
-	synchronize_rcu_mult(call_rcu, call_rcu_tasks);
+	synchronize_rcu_mult(call_rcu_hurry, call_rcu_tasks);
 
 	__bpf_struct_ops_map_free(map);
 }