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

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Message-ID: <f86de2c4-8212-4e4a-9bb5-29a6c74ac984@I-love.SAKURA.ne.jp>
Date: Mon, 29 Dec 2025 23:18:29 +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/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 2d4c5bab5af8..13b7a921cc3a 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -792,12 +792,6 @@ static void lockdep_print_held_locks(struct task_struct *p)
 	else
 		printk("%d lock%s held by %s/%d:\n", depth,
 		       str_plural(depth), p->comm, task_pid_nr(p));
-	/*
-	 * It's not reliable to print a task's held locks if it's not sleeping
-	 * and it's not the current task.
-	 */
-	if (p != current && task_is_running(p))
-		return;
 	for (i = 0; i < depth; i++) {
 		printk(" #%d: ", i);
 		print_lock(p->held_locks + i);
diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
index 58d22e2b85fc..b2abc5b65443 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_05hz(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 * 2) &&
+		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_05hz(&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 {