@@ -637,7 +637,9 @@ int __inet_hash(struct sock *sk, struct
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_stop_listen_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);
@@ -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;
}
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.de Link: https://lkml.kernel.org/r/X9CheYjuXWc75Spa@hirez.programming.kicks-ass.net --- v3…v4: - Reposted targeting the net-next tree. v2…v3: - Update commit description with ilb2 instead ilb (requested by Martin KaFai Lau). v1…v2: Reposted with fixes and net-tree as requested. Please keep in mind that this only effects the PREEMPT_RT preemption model and I'm posting this as part of the merging efforts. Therefore I didn't add the Fixes: tag and used net-next as I didn't expect any -stable backports (but then Greg sometimes backports RT-only patches since "it makes the life of some folks easier" as he puts it). net/ipv4/inet_hashtables.c | 53 ++++++++++++++++++++++++++------------------ net/ipv6/inet6_hashtables.c | 5 ---- 2 files changed, 33 insertions(+), 25 deletions(-)