[Devel] [PATCH vz10] ve/net/neighbour: do the provisional bump on tbl->gc_entries, not tbl->entries

[Konstantin Khorenko]

neigh_alloc()'s provisional counter bump was changed from tbl->gc_entries
to tbl->entries while adding the per-VE neighbour limit:

	glob_entries = atomic_inc_return(&tbl->entries) - 1;

but the success-path "atomic_inc(&tbl->entries)" was left in place, so a
successfully created non-exempt neighbour incremented tbl->entries TWICE
while neigh_destroy() decrements it only ONCE -> tbl->entries leaks +1 per
neighbour. That permanently skews the hash-grow check
(atomic_read(&tbl->entries) > (1 << hash_shift)), the gc_thresh1
short-circuit in neigh_periodic_work(), and trips the
pr_crit("neighbour leakage") check in neigh_table_clear() on unload.

Symmetrically tbl->gc_entries was no longer incremented in neigh_alloc()
at all, yet the out_entries error path still decrements it and the
gc_list machinery (neigh_mark_dead / neigh_update_gc_list) decrements it
on removal, so gc_entries drifts negative and neigh_forced_gc()'s
max_clean = gc_entries - gc_thresh2 goes large-negative, neutering forced
GC.

The upstream (and pre-patch base) neigh_alloc() does the provisional bump
on tbl->gc_entries and the single real bump on tbl->entries on success.
Restore that: bump gc_entries provisionally. tbl->entries is now
incremented once (success) and decremented once (neigh_destroy); the
per-VE counter and the gc_thresh3 limit are unchanged.

Fixes: 35b80673b07b ("ve/net/neighbour: per-ct limit for neighbour entries")
https://virtuozzo.atlassian.net/browse/VSTOR-132310
Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
---
 net/core/neighbour.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index eb6d2eff99f1..dad5fb78bc65 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -496,10 +496,10 @@ static struct neighbour *neigh_alloc(struct neigh_table *tbl,
 
 	/* If per-VE counter of neighbour entries exist
 	 * it will be limited by tbl->gc_thresh3
-	 * and according global counter (tbl->entries) become unlimited.
+	 * and the global gc counter (tbl->gc_entries) become unlimited.
 	 */
 
-	glob_entries = atomic_inc_return(&tbl->entries) - 1;
+	glob_entries = atomic_inc_return(&tbl->gc_entries) - 1;
 	cnt = get_perve_tbl_entries_counter(tbl, ve);
 	entries = cnt ? atomic_inc_return(cnt) - 1 : glob_entries;
 	gc_thresh3 = READ_ONCE(tbl->gc_thresh3);
-- 
2.47.1