Merge branch 'tcp_metrics-four-fixes'

Eric Dumazet says:

====================
tcp_metrics: four fixes

Looking at an inconclusive syzbot report, I was surprised
to see that tcp_metrics cache on my host was full of
useless entries, even though I have
/proc/sys/net/ipv4/tcp_no_metrics_save set to 1.

While looking more closely I found a total of four issues.
====================

Link: https://lore.kernel.org/r/20230922220356.3739090-1-edumazet@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/ipv4/tcp_metrics.c

@@ -470,11 +470,15 @@ void tcp_init_metrics(struct sock *sk)
 	u32 val, crtt = 0; /* cached RTT scaled by 8 */
 
 	sk_dst_confirm(sk);
+	/* ssthresh may have been reduced unnecessarily during.
+	 * 3WHS. Restore it back to its initial default.
+	 */
+	tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
 	if (!dst)
 		goto reset;
 
 	rcu_read_lock();
-	tm = tcp_get_metrics(sk, dst, true);
+	tm = tcp_get_metrics(sk, dst, false);
 	if (!tm) {
 		rcu_read_unlock();
 		goto reset;
@@ -489,11 +493,6 @@ void tcp_init_metrics(struct sock *sk)
 		tp->snd_ssthresh = val;
 		if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
 			tp->snd_ssthresh = tp->snd_cwnd_clamp;
-	} else {
-		/* ssthresh may have been reduced unnecessarily during.
-		 * 3WHS. Restore it back to its initial default.
-		 */
-		tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
 	}
 	val = tcp_metric_get(tm, TCP_METRIC_REORDERING);
 	if (val && tp->reordering != val)
@@ -899,22 +898,25 @@ static void tcp_metrics_flush_all(struct net *net)
 	unsigned int row;
 
 	for (row = 0; row < max_rows; row++, hb++) {
-		struct tcp_metrics_block __rcu **pp;
+		struct tcp_metrics_block __rcu **pp = &hb->chain;
 		bool match;
 
+		if (!rcu_access_pointer(*pp))
+			continue;
+
 		spin_lock_bh(&tcp_metrics_lock);
-		pp = &hb->chain;
 		for (tm = deref_locked(*pp); tm; tm = deref_locked(*pp)) {
 			match = net ? net_eq(tm_net(tm), net) :
 				!refcount_read(&tm_net(tm)->ns.count);
 			if (match) {
-				*pp = tm->tcpm_next;
+				rcu_assign_pointer(*pp, tm->tcpm_next);
 				kfree_rcu(tm, rcu_head);
 			} else {
 				pp = &tm->tcpm_next;
 			}
 		}
 		spin_unlock_bh(&tcp_metrics_lock);
+		cond_resched();
 	}
 }
 
@@ -949,7 +951,7 @@ static int tcp_metrics_nl_cmd_del(struct sk_buff *skb, struct genl_info *info)
 		if (addr_same(&tm->tcpm_daddr, &daddr) &&
 		    (!src || addr_same(&tm->tcpm_saddr, &saddr)) &&
 		    net_eq(tm_net(tm), net)) {
-			*pp = tm->tcpm_next;
+			rcu_assign_pointer(*pp, tm->tcpm_next);
 			kfree_rcu(tm, rcu_head);
 			found = true;
 		} else {