linux-kernel - Re: [syzbot] [net?] INFO: task hung in new_device

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Message-ID: <380a0d7a-391e-4c9f-9211-f61d763f28de@I-love.SAKURA.ne.jp>
Date: Mon, 29 Dec 2025 15:36:26 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: syzbot <syzbot+05f9cecd28e356241aba@...kaller.appspotmail.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [syzbot] [net?] INFO: task hung in new_device_store (5)

#syz test

diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
index 58d22e2b85fc..b6b79972b50b 100644
--- a/net/bridge/br_fdb.c
+++ b/net/bridge/br_fdb.c
@@ -982,6 +982,15 @@ static bool __fdb_mark_active(struct net_bridge_fdb_entry *fdb)
 		  test_and_clear_bit(BR_FDB_NOTIFY_INACTIVE, &fdb->flags));
 }
 
+static bool ratelimit_1hz(unsigned long *stamp)
+{
+	const unsigned long now = data_race(READ_ONCE(jiffies));
+	const unsigned long prev = data_race(READ_ONCE(*stamp));
+
+	return !time_in_range_open(now, prev, prev + HZ) &&
+		cmpxchg(stamp, prev, now) == prev;
+}
+
 void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
 		   const unsigned char *addr, u16 vid, unsigned long flags)
 {
@@ -995,7 +1004,9 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
 	if (likely(fdb)) {
 		/* attempt to update an entry for a local interface */
 		if (unlikely(test_bit(BR_FDB_LOCAL, &fdb->flags))) {
-			if (net_ratelimit())
+			static unsigned long stamp;
+
+			if (ratelimit_1hz(&stamp))
 				br_warn(br, "received packet on %s with own address as source address (addr:%pM, vlan:%u)\n",
 					source->dev->name, addr, vid);
 		} else {