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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>,
	Daniel Bristot de Oliveira <bristot@kernel.org>,
	Boqun Feng <boqun.feng@gmail.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Eric Dumazet <edumazet@google.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	Ingo Molnar <mingo@redhat.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Paolo Abeni <pabeni@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Waiman Long <longman@redhat.com>,
	Will Deacon <will@kernel.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>,
	Hao Luo <haoluo@google.com>,
	Jiri Olsa <jolsa@kernel.org>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	Martin KaFai Lau <martin.lau@linux.dev>,
	Song Liu <song@kernel.org>,
	Stanislav Fomichev <sdf@google.com>,
	Yonghong Song <yonghong.song@linux.dev>,
	bpf@vger.kernel.org
Subject: [PATCH v6 net-next 13/15] net: Use nested-BH locking for bpf_scratchpad.
Date: Wed, 12 Jun 2024 18:44:39 +0200
Message-ID: <20240612170303.3896084-14-bigeasy@linutronix.de>
In-Reply-To: <20240612170303.3896084-1-bigeasy@linutronix.de>
References: <20240612170303.3896084-1-bigeasy@linutronix.de>
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bpf_scratchpad is a per-CPU variable and relies on disabled BH for its
locking. Without per-CPU locking in local_bh_disable() on PREEMPT_RT
this data structure requires explicit locking.

Add a local_lock_t to the data structure and use local_lock_nested_bh()
for locking. This change adds only lockdep coverage and does not alter
the functional behaviour for !PREEMPT_RT.

Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Hao Luo <haoluo@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Song Liu <song@kernel.org>
Cc: Stanislav Fomichev <sdf@google.com>
Cc: Yonghong Song <yonghong.song@linux.dev>
Cc: bpf@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 net/core/filter.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index ba1a739a9bedc..fbcfd563dccfd 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1658,9 +1658,12 @@ struct bpf_scratchpad {
 		__be32 diff[MAX_BPF_STACK / sizeof(__be32)];
 		u8     buff[MAX_BPF_STACK];
 	};
+	local_lock_t	bh_lock;
 };
=20
-static DEFINE_PER_CPU(struct bpf_scratchpad, bpf_sp);
+static DEFINE_PER_CPU(struct bpf_scratchpad, bpf_sp) =3D {
+	.bh_lock	=3D INIT_LOCAL_LOCK(bh_lock),
+};
=20
 static inline int __bpf_try_make_writable(struct sk_buff *skb,
 					  unsigned int write_len)
@@ -2016,6 +2019,7 @@ BPF_CALL_5(bpf_csum_diff, __be32 *, from, u32, from_s=
ize,
 	struct bpf_scratchpad *sp =3D this_cpu_ptr(&bpf_sp);
 	u32 diff_size =3D from_size + to_size;
 	int i, j =3D 0;
+	__wsum ret;
=20
 	/* This is quite flexible, some examples:
 	 *
@@ -2029,12 +2033,15 @@ BPF_CALL_5(bpf_csum_diff, __be32 *, from, u32, from=
_size,
 		     diff_size > sizeof(sp->diff)))
 		return -EINVAL;
=20
+	local_lock_nested_bh(&bpf_sp.bh_lock);
 	for (i =3D 0; i < from_size / sizeof(__be32); i++, j++)
 		sp->diff[j] =3D ~from[i];
 	for (i =3D 0; i <   to_size / sizeof(__be32); i++, j++)
 		sp->diff[j] =3D to[i];
=20
-	return csum_partial(sp->diff, diff_size, seed);
+	ret =3D csum_partial(sp->diff, diff_size, seed);
+	local_unlock_nested_bh(&bpf_sp.bh_lock);
+	return ret;
 }
=20
 static const struct bpf_func_proto bpf_csum_diff_proto =3D {
--=20
2.45.1