Re: [RT] 5.9-rt14 softirq_ctrl.lock vs listening_hash[i].lock lockdep splat

[Sebastian Andrzej Siewior]

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 <bige...@linutronix.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