linux-kernel - Re: [RT] 5.9-rt14 softirq_ctrl.lock vs listening

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Date:   Mon, 12 Oct 2020 18:45:53 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Mike Galbraith <efault@....de>
Cc:     tglx@...utronix.de, linux-rt-users@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RT] 5.9-rt14  softirq_ctrl.lock vs listening_hash[i].lock
 lockdep splat

On 2020-10-10 06:31:57 [+0200], Mike Galbraith wrote:

so this then. Do you have more of these?

----------->8--------------------
Subject: [PATCH] tcp: Remove superfluous BH-disable around listening_hash

Commit
   9652dc2eb9e40 ("tcp: relax listening_hash operations")

removed the need to disable bottom half while acquiring
listening_hash.lock. There are still two callers left which disable
bottom half before the lock is acquired.

Drop local_bh_disable() around __inet_hash() which acquires
listening_hash->lock, invoke inet_ehash_nolisten() with disabled BH.
inet_unhash() conditionally acquires listening_hash->lock.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 net/ipv4/inet_hashtables.c  | 19 ++++++++++++-------
 net/ipv6/inet6_hashtables.c |  5 +----
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 239e54474b653..fcb105cbb5465 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -585,7 +585,9 @@ int __inet_hash(struct sock *sk, struct sock *osk)
 	int err = 0;
 
 	if (sk->sk_state != TCP_LISTEN) {
+		local_bh_disable();
 		inet_ehash_nolisten(sk, osk);
+		local_bh_enable();
 		return 0;
 	}
 	WARN_ON(!sk_unhashed(sk));
@@ -617,11 +619,8 @@ int inet_hash(struct sock *sk)
 {
 	int err = 0;
 
-	if (sk->sk_state != TCP_CLOSE) {
-		local_bh_disable();
+	if (sk->sk_state != TCP_CLOSE)
 		err = __inet_hash(sk, NULL);
-		local_bh_enable();
-	}
 
 	return err;
 }
@@ -632,17 +631,20 @@ void inet_unhash(struct sock *sk)
 	struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
 	struct inet_listen_hashbucket *ilb = NULL;
 	spinlock_t *lock;
+	bool state_listen;
 
 	if (sk_unhashed(sk))
 		return;
 
 	if (sk->sk_state == TCP_LISTEN) {
+		state_listen = true;
 		ilb = &hashinfo->listening_hash[inet_sk_listen_hashfn(sk)];
-		lock = &ilb->lock;
+		spin_lock(&ilb->lock);
 	} else {
+		state_listen = false;
 		lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
+		spin_lock_bh(lock);
 	}
-	spin_lock_bh(lock);
 	if (sk_unhashed(sk))
 		goto unlock;
 
@@ -655,7 +657,10 @@ void inet_unhash(struct sock *sk)
 	__sk_nulls_del_node_init_rcu(sk);
 	sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
 unlock:
-	spin_unlock_bh(lock);
+	if (state_listen)
+		spin_unlock(&ilb->lock);
+	else
+		spin_unlock_bh(lock);
 }
 EXPORT_SYMBOL_GPL(inet_unhash);
 
diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c
index 2d3add9e61162..50fd17cbf3ec7 100644
--- a/net/ipv6/inet6_hashtables.c
+++ b/net/ipv6/inet6_hashtables.c
@@ -335,11 +335,8 @@ int inet6_hash(struct sock *sk)
 {
 	int err = 0;
 
-	if (sk->sk_state != TCP_CLOSE) {
-		local_bh_disable();
+	if (sk->sk_state != TCP_CLOSE)
 		err = __inet_hash(sk, NULL);
-		local_bh_enable();
-	}
 
 	return err;
 }
-- 
2.28.0