From: Sebastian Andrzej Siewior bigeasy@linutronix.de
[ Upstream commit 4f9bf2a2f5aacf988e6d5e56b961ba45c5a25248 ]
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.
On PREEMPT_RT the softirqs are preemptible and local_bh_disable() acts as a lock to ensure that resources, that are protected by disabling bottom halves, remain protected. This leads to a circular locking dependency if the lock acquired with disabled bottom halves is also acquired with enabled bottom halves followed by disabling bottom halves. This is the reverse locking order. It has been observed with inet_listen_hashbucket::lock:
local_bh_disable() + spin_lock(&ilb->lock): inet_listen() inet_csk_listen_start() sk->sk_prot->hash() := inet_hash() local_bh_disable() __inet_hash() spin_lock(&ilb->lock); acquire(&ilb->lock);
Reverse order: spin_lock(&ilb2->lock) + local_bh_disable(): tcp_seq_next() listening_get_next() spin_lock(&ilb2->lock); acquire(&ilb2->lock);
tcp4_seq_show() get_tcp4_sock() sock_i_ino() read_lock_bh(&sk->sk_callback_lock); acquire(softirq_ctrl) // <---- whoops acquire(&sk->sk_callback_lock)
Drop local_bh_disable() around __inet_hash() which acquires listening_hash->lock. Split inet_unhash() and acquire the listen_hashbucket lock without disabling bottom halves; the inet_ehash lock with disabled bottom halves.
Reported-by: Mike Galbraith efault@gmx.de Signed-off-by: Sebastian Andrzej Siewior bigeasy@linutronix.de Link: https://lkml.kernel.org/r/12d6f9879a97cd56c09fb53dee343cbb14f7f1f7.camel@gmx... Link: https://lkml.kernel.org/r/X9CheYjuXWc75Spa@hirez.programming.kicks-ass.net Link: https://lore.kernel.org/r/YgQOebeZ10eNx1W6@linutronix.de Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/inet_hashtables.c | 53 ++++++++++++++++++++++--------------- net/ipv6/inet6_hashtables.c | 5 +--- 2 files changed, 33 insertions(+), 25 deletions(-)
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c index e093847c334d..915b8e1bd9ef 100644 --- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c @@ -637,7 +637,9 @@ 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, NULL); + local_bh_enable(); return 0; } WARN_ON(!sk_unhashed(sk)); @@ -669,45 +671,54 @@ 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; } EXPORT_SYMBOL_GPL(inet_hash);
-void inet_unhash(struct sock *sk) +static void __inet_unhash(struct sock *sk, struct inet_listen_hashbucket *ilb) { - struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo; - struct inet_listen_hashbucket *ilb = NULL; - spinlock_t *lock; - if (sk_unhashed(sk)) return;
- if (sk->sk_state == TCP_LISTEN) { - ilb = &hashinfo->listening_hash[inet_sk_listen_hashfn(sk)]; - lock = &ilb->lock; - } else { - lock = inet_ehash_lockp(hashinfo, sk->sk_hash); - } - spin_lock_bh(lock); - if (sk_unhashed(sk)) - goto unlock; - if (rcu_access_pointer(sk->sk_reuseport_cb)) reuseport_detach_sock(sk); if (ilb) { + struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo; + inet_unhash2(hashinfo, sk); ilb->count--; } __sk_nulls_del_node_init_rcu(sk); sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1); -unlock: - spin_unlock_bh(lock); +} + +void inet_unhash(struct sock *sk) +{ + struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo; + + if (sk_unhashed(sk)) + return; + + if (sk->sk_state == TCP_LISTEN) { + struct inet_listen_hashbucket *ilb; + + ilb = &hashinfo->listening_hash[inet_sk_listen_hashfn(sk)]; + /* Don't disable bottom halves while acquiring the lock to + * avoid circular locking dependency on PREEMPT_RT. + */ + spin_lock(&ilb->lock); + __inet_unhash(sk, ilb); + spin_unlock(&ilb->lock); + } else { + spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash); + + spin_lock_bh(lock); + __inet_unhash(sk, NULL); + spin_unlock_bh(lock); + } } EXPORT_SYMBOL_GPL(inet_unhash);
diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c index 67c9114835c8..0a2e7f228391 100644 --- a/net/ipv6/inet6_hashtables.c +++ b/net/ipv6/inet6_hashtables.c @@ -333,11 +333,8 @@ 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; }