netdev - [Patch bpf] sock_map: convert cancel_work_sync() to cancel

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Date:   Mon, 17 Oct 2022 19:02:58 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Sitnicki <jakub@...udflare.com>
Subject: [Patch bpf] sock_map: convert cancel_work_sync() to cancel_work()

From: Cong Wang <cong.wang@...edance.com>

Technically we don't need lock the sock in the psock work, but we
need to prevent this work running in parallel with sock_map_close().

With this, we no longer need to wait for the psock->work synchronously,
because when we reach here, either this work is still pending, or
blocking on the lock_sock(), or it is completed. We only need to cancel
the first case asynchronously, and we need to bail out the second case
quickly by checking SK_PSOCK_TX_ENABLED bit.

Fixes: 799aa7f98d53 ("skmsg: Avoid lock_sock() in sk_psock_backlog()")
Reported-by: Stanislav Fomichev <sdf@...gle.com>
Cc: John Fastabend <john.fastabend@...il.com>
Cc: Jakub Sitnicki <jakub@...udflare.com>
Signed-off-by: Cong Wang <cong.wang@...edance.com>
---
 include/linux/skmsg.h |  2 +-
 net/core/skmsg.c      | 19 +++++++++++++------
 net/core/sock_map.c   |  4 ++--
 3 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
index 48f4b645193b..70d6cb94e580 100644
--- a/include/linux/skmsg.h
+++ b/include/linux/skmsg.h
@@ -376,7 +376,7 @@ static inline void sk_psock_report_error(struct sk_psock *psock, int err)
 }
 
 struct sk_psock *sk_psock_init(struct sock *sk, int node);
-void sk_psock_stop(struct sk_psock *psock, bool wait);
+void sk_psock_stop(struct sk_psock *psock);
 
 #if IS_ENABLED(CONFIG_BPF_STREAM_PARSER)
 int sk_psock_init_strp(struct sock *sk, struct sk_psock *psock);
diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index ca70525621c7..c329e71ea924 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -647,6 +647,11 @@ static void sk_psock_backlog(struct work_struct *work)
 	int ret;
 
 	mutex_lock(&psock->work_mutex);
+	lock_sock(psock->sk);
+
+	if (!sk_psock_test_state(psock, SK_PSOCK_TX_ENABLED))
+		goto end;
+
 	if (unlikely(state->skb)) {
 		spin_lock_bh(&psock->ingress_lock);
 		skb = state->skb;
@@ -672,9 +677,12 @@ static void sk_psock_backlog(struct work_struct *work)
 		skb_bpf_redirect_clear(skb);
 		do {
 			ret = -EIO;
-			if (!sock_flag(psock->sk, SOCK_DEAD))
+			if (!sock_flag(psock->sk, SOCK_DEAD)) {
+				release_sock(psock->sk);
 				ret = sk_psock_handle_skb(psock, skb, off,
 							  len, ingress);
+				lock_sock(psock->sk);
+			}
 			if (ret <= 0) {
 				if (ret == -EAGAIN) {
 					sk_psock_skb_state(psock, state, skb,
@@ -695,6 +703,7 @@ static void sk_psock_backlog(struct work_struct *work)
 			kfree_skb(skb);
 	}
 end:
+	release_sock(psock->sk);
 	mutex_unlock(&psock->work_mutex);
 }
 
@@ -803,16 +812,14 @@ static void sk_psock_link_destroy(struct sk_psock *psock)
 	}
 }
 
-void sk_psock_stop(struct sk_psock *psock, bool wait)
+void sk_psock_stop(struct sk_psock *psock)
 {
 	spin_lock_bh(&psock->ingress_lock);
 	sk_psock_clear_state(psock, SK_PSOCK_TX_ENABLED);
 	sk_psock_cork_free(psock);
 	__sk_psock_zap_ingress(psock);
 	spin_unlock_bh(&psock->ingress_lock);
-
-	if (wait)
-		cancel_work_sync(&psock->work);
+	cancel_work(&psock->work);
 }
 
 static void sk_psock_done_strp(struct sk_psock *psock);
@@ -850,7 +857,7 @@ void sk_psock_drop(struct sock *sk, struct sk_psock *psock)
 		sk_psock_stop_verdict(sk, psock);
 	write_unlock_bh(&sk->sk_callback_lock);
 
-	sk_psock_stop(psock, false);
+	sk_psock_stop(psock);
 
 	INIT_RCU_WORK(&psock->rwork, sk_psock_destroy);
 	queue_rcu_work(system_wq, &psock->rwork);
diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index a660baedd9e7..d4e11d7f459c 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -1596,7 +1596,7 @@ void sock_map_destroy(struct sock *sk)
 	saved_destroy = psock->saved_destroy;
 	sock_map_remove_links(sk, psock);
 	rcu_read_unlock();
-	sk_psock_stop(psock, false);
+	sk_psock_stop(psock);
 	sk_psock_put(sk, psock);
 	saved_destroy(sk);
 }
@@ -1619,7 +1619,7 @@ void sock_map_close(struct sock *sk, long timeout)
 	saved_close = psock->saved_close;
 	sock_map_remove_links(sk, psock);
 	rcu_read_unlock();
-	sk_psock_stop(psock, true);
+	sk_psock_stop(psock);
 	sk_psock_put(sk, psock);
 	release_sock(sk);
 	saved_close(sk, timeout);
-- 
2.34.1