[PATCH net] batman-adv: reduce softirq drain in tt_purge loops

["Ömer Mete Kaya" <omermetekaya0@gmail.com>]

Replace per-bucket spin_lock_bh()/spin_unlock_bh() with outer
local_bh_disable()/enable() and periodic drain every 64 buckets
to avoid excessive softirq processing during TT purge.

Add may_sleep parameter to batadv_tt_local_purge() since it is
called both from workqueue context (where cond_resched is safe)
and under commit_lock spinlock in batadv_tt_local_resize_to_mtu()
(where sleeping is not allowed).

Fixes: c6c8fea29769 ("net: Add batman-adv meshing protocol")
Reported-by: syzbot+61b202fdc410840f0198@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=61b202fdc410840f0198
Signed-off-by: Ömer Mete Kaya <omermetekaya0@gmail.com>
---
 net/batman-adv/translation-table.c | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/net/batman-adv/translation-table.c b/net/batman-adv/translation-table.c
index 68f79853032e..915f5589e056 100644
--- a/net/batman-adv/translation-table.c
+++ b/net/batman-adv/translation-table.c
@@ -1386,21 +1386,29 @@ static void batadv_tt_local_purge_list(struct batadv_priv *bat_priv,
  *  inactive or not
  */
 static void batadv_tt_local_purge(struct batadv_priv *bat_priv,
-				  int timeout)
+				  int timeout, bool may_sleep)
 {
 	spinlock_t *list_lock; /* protects write access to the hash lists */
 	struct batadv_hashtable *hash = bat_priv->tt.local_hash;
 	struct hlist_head *head;
 	u32 i;

+	local_bh_disable();
 	for (i = 0; i < hash->size; i++) {
 		head = &hash->table[i];
 		list_lock = &hash->list_locks[i];

-		spin_lock_bh(list_lock);
+		spin_lock(list_lock);
 		batadv_tt_local_purge_list(bat_priv, head, timeout);
-		spin_unlock_bh(list_lock);
+		spin_unlock(list_lock);
+
+		if (may_sleep && (i & 63) == 63) {
+			local_bh_enable();
+			cond_resched();
+			local_bh_disable();
+		}
 	}
+	local_bh_enable();
 }

 /**
@@ -2363,11 +2371,12 @@ static void batadv_tt_global_purge(struct batadv_priv *bat_priv)
 	char *msg = NULL;
 	u32 i;

+	local_bh_disable();
 	for (i = 0; i < hash->size; i++) {
 		head = &hash->table[i];
 		list_lock = &hash->list_locks[i];

-		spin_lock_bh(list_lock);
+		spin_lock(list_lock);
 		hlist_for_each_entry_safe(tt_common, node_tmp, head,
 					  hash_entry) {
 			tt_global = container_of(tt_common,
@@ -2387,8 +2396,15 @@ static void batadv_tt_global_purge(struct batadv_priv *bat_priv)

 			batadv_tt_global_entry_put(tt_global);
 		}
-		spin_unlock_bh(list_lock);
+		spin_unlock(list_lock);
+
+		if ((i & 63) == 63) {
+			local_bh_enable();
+			cond_resched();
+			local_bh_disable();
+		}
 	}
+	local_bh_enable();
 }

 /**
@@ -3750,7 +3766,7 @@ static void batadv_tt_purge(struct work_struct *work)
 	priv_tt = container_of(delayed_work, struct batadv_priv_tt, work);
 	bat_priv = container_of(priv_tt, struct batadv_priv, tt);

-	batadv_tt_local_purge(bat_priv, BATADV_TT_LOCAL_TIMEOUT);
+	batadv_tt_local_purge(bat_priv, BATADV_TT_LOCAL_TIMEOUT, true);
 	batadv_tt_global_purge(bat_priv);
 	batadv_tt_req_purge(bat_priv);
 	batadv_tt_roam_purge(bat_priv);
@@ -4156,7 +4172,7 @@ void batadv_tt_local_resize_to_mtu(struct net_device *mesh_iface)
 		if (packet_size_max >= table_size)
 			break;

-		batadv_tt_local_purge(bat_priv, timeout);
+		batadv_tt_local_purge(bat_priv, timeout, false);
 		batadv_tt_local_purge_pending_clients(bat_priv);

 		timeout /= 2;
--
2.56.0