netfilter: nf_conntrack: use mod_timer_pending() for conntrack refresh

Use mod_timer_pending() instead of atomic sequence of del_timer()/
add_timer(). mod_timer_pending() does not rearm an inactive timer,
so we don't need the conntrack lock anymore to make sure we don't
accidentally rearm a timer of a conntrack which is in the process
of being destroyed.

With this change, we don't need to take the global lock anymore at all,
counter updates can be performed under the per-conntrack lock.
Signed-off-by: Patrick McHardy <kaber@trash.net>

net/netfilter/nf_conntrack_core.c

@@ -807,8 +807,6 @@ void __nf_ct_refresh_acct(struct nf_conn *ct,
 	NF_CT_ASSERT(ct->timeout.data == (unsigned long)ct);
 	NF_CT_ASSERT(skb);
 
-	spin_lock_bh(&nf_conntrack_lock);
-
 	/* Only update if this is not a fixed timeout */
 	if (test_bit(IPS_FIXED_TIMEOUT_BIT, &ct->status))
 		goto acct;
@@ -822,11 +820,8 @@ void __nf_ct_refresh_acct(struct nf_conn *ct,
 		/* Only update the timeout if the new timeout is at least
 		   HZ jiffies from the old timeout. Need del_timer for race
 		   avoidance (may already be dying). */
-		if (newtime - ct->timeout.expires >= HZ
-		    && del_timer(&ct->timeout)) {
-			ct->timeout.expires = newtime;
-			add_timer(&ct->timeout);
-		}
+		if (newtime - ct->timeout.expires >= HZ)
+			mod_timer_pending(&ct->timeout, newtime);
 	}
 
 acct:
@@ -835,13 +830,13 @@ acct:
 
 		acct = nf_conn_acct_find(ct);
 		if (acct) {
+			spin_lock_bh(&ct->lock);
 			acct[CTINFO2DIR(ctinfo)].packets++;
 			acct[CTINFO2DIR(ctinfo)].bytes +=
 				skb->len - skb_network_offset(skb);
+			spin_unlock_bh(&ct->lock);
 		}
 	}
-
-	spin_unlock_bh(&nf_conntrack_lock);
 }
 EXPORT_SYMBOL_GPL(__nf_ct_refresh_acct);
 
@@ -853,14 +848,14 @@ bool __nf_ct_kill_acct(struct nf_conn *ct,
 	if (do_acct) {
 		struct nf_conn_counter *acct;
 
-		spin_lock_bh(&nf_conntrack_lock);
 		acct = nf_conn_acct_find(ct);
 		if (acct) {
+			spin_lock_bh(&ct->lock);
 			acct[CTINFO2DIR(ctinfo)].packets++;
 			acct[CTINFO2DIR(ctinfo)].bytes +=
 				skb->len - skb_network_offset(skb);
+			spin_unlock_bh(&ct->lock);
 		}
-		spin_unlock_bh(&nf_conntrack_lock);
 	}
 
 	if (del_timer(&ct->timeout)) {