[Devel] [PATCH RHEL10 COMMIT] ve/net/neighbour: keep the per-VE counter in sync with tbl->gc_entries

[Konstantin Khorenko]

The commit is pushed to "branch-rh10-6.12.0-211.16.1.12.x.vz10-ovz" and will appear at git at bitbucket.org:openvz/vzkernel.git
after rh10-6.12.0-211.16.1.12.1.vz10
------>
commit a99b1698129bd46dd8c56c9fa07e01921890d15c
Author: Konstantin Khorenko <khorenko at virtuozzo.com>
Date:   Mon Jun 15 17:43:55 2026 +0200

    ve/net/neighbour: keep the per-VE counter in sync with tbl->gc_entries
    
    The per-VE neighbour counter (ve->arp_neigh_nr / nd_neigh_nr, selected by
    get_perve_tbl_entries_counter()) was incremented only on the gc-eligible
    path of neigh_alloc() - exempt_from_gc neighbours skip it - but
    neigh_destroy() decremented it unconditionally for every neighbour. So
    each exempt_from_gc neighbour (loopback device, NUD_PERMANENT or
    NTF_EXT_LEARNED) decremented the per-VE counter without a matching
    increment, driving it negative over time. Once it is negative the per-CT
    limit check "entries >= gc_thresh3" in neigh_alloc() never trips and the
    per-container neighbour limit silently stops working.
    
    Make the per-VE counter a true per-VE mirror of tbl->gc_entries: change
    it at exactly the same sites where gc_entries changes (it already did in
    neigh_alloc()'s provisional path and in the out_entries error path):
     - neigh_update_gc_list(): inc/dec it together with gc_entries when the
       neighbour joins/leaves the gc list on a state change;
     - neigh_mark_dead(): dec it when the neighbour leaves the gc list;
     - ___neigh_create() out_neigh_release: dec it (it previously undid only
       gc_entries, leaking the per-VE counter on that error path);
    and drop the unconditional decrement from neigh_destroy(). The per-VE
    counter is now incremented and decremented exactly for gc-eligible
    neighbours, like gc_entries; exempt_from_gc neighbours never touch it.
    
    get_perve_tbl_entries_counter() is moved above neigh_mark_dead() so the
    gc-list helpers can use it.
    
    Fixes: 5f0a2a6f78f7 ("ve/net/neighbour: per-ct limit for neighbour entries")
    https://virtuozzo.atlassian.net/browse/VSTOR-132310
    Feature: net: make the neighbor entries limit per-CT
    
    Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
    Reported-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
    Reviewed-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
 net/core/neighbour.c | 47 ++++++++++++++++++++++++++++++-----------------
 1 file changed, 30 insertions(+), 17 deletions(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index dad5fb78bc65..cf1f11a596d8 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -116,12 +116,29 @@ unsigned long neigh_rand_reach_time(unsigned long base)
 }
 EXPORT_SYMBOL(neigh_rand_reach_time);
 
+static inline atomic_t *get_perve_tbl_entries_counter(struct neigh_table *tbl,
+							struct ve_struct *ve)
+{
+	switch (tbl->family) {
+	case AF_INET:
+		return &ve->arp_neigh_nr;
+	case AF_INET6:
+		return &ve->nd_neigh_nr;
+	}
+	return NULL;
+}
+
 static void neigh_mark_dead(struct neighbour *n)
 {
 	n->dead = 1;
 	if (!list_empty(&n->gc_list)) {
+		atomic_t *cnt = get_perve_tbl_entries_counter(n->tbl,
+						dev_net(n->dev)->owner_ve);
+
 		list_del_init(&n->gc_list);
 		atomic_dec(&n->tbl->gc_entries);
+		if (cnt)
+			atomic_dec(cnt);
 	}
 	if (!list_empty(&n->managed_list))
 		list_del_init(&n->managed_list);
@@ -129,6 +146,8 @@ static void neigh_mark_dead(struct neighbour *n)
 
 static void neigh_update_gc_list(struct neighbour *n)
 {
+	atomic_t *cnt = get_perve_tbl_entries_counter(n->tbl,
+					dev_net(n->dev)->owner_ve);
 	bool on_gc_list, exempt_from_gc;
 
 	write_lock_bh(&n->tbl->lock);
@@ -146,10 +165,14 @@ static void neigh_update_gc_list(struct neighbour *n)
 	if (exempt_from_gc && on_gc_list) {
 		list_del_init(&n->gc_list);
 		atomic_dec(&n->tbl->gc_entries);
+		if (cnt)
+			atomic_dec(cnt);
 	} else if (!exempt_from_gc && !on_gc_list) {
 		/* add entries to the tail; cleaning removes from the front */
 		list_add_tail(&n->gc_list, &n->tbl->gc_list);
 		atomic_inc(&n->tbl->gc_entries);
+		if (cnt)
+			atomic_inc(cnt);
 	}
 out:
 	write_unlock(&n->lock);
@@ -469,18 +492,6 @@ int neigh_ifdown(struct neigh_table *tbl, struct net_device *dev)
 }
 EXPORT_SYMBOL(neigh_ifdown);
 
-static inline atomic_t *get_perve_tbl_entries_counter(struct neigh_table *tbl,
-							struct ve_struct *ve)
-{
-	switch (tbl->family) {
-	case AF_INET:
-		return &ve->arp_neigh_nr;
-	case AF_INET6:
-		return &ve->nd_neigh_nr;
-	}
-	return NULL;
-}
-
 static struct neighbour *neigh_alloc(struct neigh_table *tbl,
 				     struct net_device *dev,
 				     u32 flags, bool exempt_from_gc)
@@ -761,8 +772,14 @@ ___neigh_create(struct neigh_table *tbl, const void *pkey,
 out_tbl_unlock:
 	write_unlock_bh(&tbl->lock);
 out_neigh_release:
-	if (!exempt_from_gc)
+	if (!exempt_from_gc) {
+		atomic_t *cnt = get_perve_tbl_entries_counter(tbl,
+						dev_net(dev)->owner_ve);
+
 		atomic_dec(&tbl->gc_entries);
+		if (cnt)
+			atomic_dec(cnt);
+	}
 	neigh_release(n);
 	goto out;
 }
@@ -927,8 +944,6 @@ static inline void neigh_parms_put(struct neigh_parms *parms)
 void neigh_destroy(struct neighbour *neigh)
 {
 	struct net_device *dev = neigh->dev;
-	struct ve_struct *ve = dev_net(dev)->owner_ve;
-	atomic_t *cnt = get_perve_tbl_entries_counter(neigh->tbl, ve);
 
 	NEIGH_CACHE_STAT_INC(neigh->tbl, destroys);
 
@@ -954,8 +969,6 @@ void neigh_destroy(struct neighbour *neigh)
 
 	neigh_dbg(2, "neigh %p is destroyed\n", neigh);
 
-	if (cnt)
-		 atomic_dec(cnt);
 	atomic_dec(&neigh->tbl->entries);
 	kfree_rcu(neigh, rcu);
 }