[PATCH v2 net-next 02/13] neighbour: Remove lock dance for neigh_update_{gc,managed}_list().

[Kuniyuki Iwashima <kuniyu@google.com>]

__neigh_update() could call neigh_update_gc_list() and
neigh_update_managed_list().

Both of them acquire neigh->tbl->lock and neigh->lock, check
neigh->dead, perform link operations, and release the locks.

Let's remove the lock dance.

Note that neigh->dead is always marked under neigh->tbl->lock.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 net/core/neighbour.c | 39 +++++++++++++++++++--------------------
 1 file changed, 19 insertions(+), 20 deletions(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 69a5f9dfa851..13eea09721c6 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -135,6 +135,8 @@ EXPORT_SYMBOL(neigh_rand_reach_time);
 
 static void neigh_mark_dead(struct neighbour *n)
 {
+	lockdep_assert_held(&n->tbl->lock);
+
 	n->dead = 1;
 	if (!list_empty(&n->gc_list)) {
 		list_del_init(&n->gc_list);
@@ -148,11 +150,6 @@ static void neigh_update_gc_list(struct neighbour *n)
 {
 	bool on_gc_list, exempt_from_gc;
 
-	spin_lock_bh(&n->tbl->lock);
-	write_lock(&n->lock);
-	if (n->dead)
-		goto out;
-
 	/* remove from the gc list if new state is permanent or if neighbor is
 	 * externally learned / validated; otherwise entry should be on the gc
 	 * list
@@ -169,20 +166,12 @@ static void neigh_update_gc_list(struct neighbour *n)
 		list_add_tail(&n->gc_list, &n->tbl->gc_list);
 		atomic_inc(&n->tbl->gc_entries);
 	}
-out:
-	write_unlock(&n->lock);
-	spin_unlock_bh(&n->tbl->lock);
 }
 
 static void neigh_update_managed_list(struct neighbour *n)
 {
 	bool on_managed_list, add_to_managed;
 
-	spin_lock_bh(&n->tbl->lock);
-	write_lock(&n->lock);
-	if (n->dead)
-		goto out;
-
 	add_to_managed = n->flags & NTF_MANAGED;
 	on_managed_list = !list_empty(&n->managed_list);
 
@@ -190,9 +179,6 @@ static void neigh_update_managed_list(struct neighbour *n)
 		list_del_init(&n->managed_list);
 	else if (add_to_managed && !on_managed_list)
 		list_add_tail(&n->managed_list, &n->tbl->managed_list);
-out:
-	write_unlock(&n->lock);
-	spin_unlock_bh(&n->tbl->lock);
 }
 
 static void neigh_update_flags(struct neighbour *neigh, u32 flags, int *notify,
@@ -1523,10 +1509,23 @@ static int __neigh_update(struct neighbour *neigh, const u8 *lladdr,
 
 	write_unlock_bh(&neigh->lock);
 
-	if (((new ^ old) & NUD_PERMANENT) || gc_update)
-		neigh_update_gc_list(neigh);
-	if (managed_update)
-		neigh_update_managed_list(neigh);
+	gc_update |= !!((new ^ old) & NUD_PERMANENT);
+	if (gc_update || managed_update) {
+		spin_lock_bh(&neigh->tbl->lock);
+
+		if (!neigh->dead) {
+			write_lock(&neigh->lock);
+
+			if (gc_update)
+				neigh_update_gc_list(neigh);
+			if (managed_update)
+				neigh_update_managed_list(neigh);
+
+			write_unlock(&neigh->lock);
+		}
+
+		spin_unlock_bh(&neigh->tbl->lock);
+	}
 
 	if (notify)
 		call_netevent_notifiers(NETEVENT_NEIGH_UPDATE, neigh);
-- 
2.55.0.679.g6767b8d81c-goog