linux-kernel - [PATCH net] net: bridge: fix soft lockup in br_multicast_query

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Message-ID: <20250806094941.1285944-1-wangliang74@huawei.com>
Date: Wed, 6 Aug 2025 17:49:41 +0800
From: Wang Liang <wangliang74@...wei.com>
To: <razor@...ckwall.org>, <idosch@...dia.com>, <davem@...emloft.net>,
	<edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
	<horms@...nel.org>
CC: <bridge@...ts.linux.dev>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <yuehaibing@...wei.com>,
	<zhangchangzhong@...wei.com>, <wangliang74@...wei.com>
Subject: [PATCH net] net: bridge: fix soft lockup in br_multicast_query_expired()

When set multicast_query_interval to a large value, the local variable
'time' in br_multicast_send_query() may overflow. If the time is smaller
than jiffies, the timer will expire immediately, and then call mod_timer()
again, which creates a loop and may trigger the following soft lockup
issue:

  watchdog: BUG: soft lockup - CPU#1 stuck for 221s! [rb_consumer:66]
  CPU: 1 UID: 0 PID: 66 Comm: rb_consumer Not tainted 6.16.0+ #259 PREEMPT(none)
  Call Trace:
   <IRQ>
   __netdev_alloc_skb+0x2e/0x3a0
   br_ip6_multicast_alloc_query+0x212/0x1b70
   __br_multicast_send_query+0x376/0xac0
   br_multicast_send_query+0x299/0x510
   br_multicast_query_expired.constprop.0+0x16d/0x1b0
   call_timer_fn+0x3b/0x2a0
   __run_timers+0x619/0x950
   run_timer_softirq+0x11c/0x220
   handle_softirqs+0x18e/0x560
   __irq_exit_rcu+0x158/0x1a0
   sysvec_apic_timer_interrupt+0x76/0x90
   </IRQ>

This issue can be reproduced with:
  ip link add br0 type bridge
  echo 1 > /sys/class/net/br0/bridge/multicast_querier
  echo 0xffffffffffffffff >
  	/sys/class/net/br0/bridge/multicast_query_interval
  ip link set dev br0 up

Fix this by comparing expire time with jiffies, to avoid the timer loop.

Fixes: 7e4df51eb35d ("bridge: netlink: add support for igmp's intervals")
Signed-off-by: Wang Liang <wangliang74@...wei.com>
---
 net/bridge/br_multicast.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 1377f31b719c..631ae3b4c45d 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1892,7 +1892,8 @@ static void br_multicast_send_query(struct net_bridge_mcast *brmctx,
 	time += own_query->startup_sent < brmctx->multicast_startup_query_count ?
 		brmctx->multicast_startup_query_interval :
 		brmctx->multicast_query_interval;
-	mod_timer(&own_query->timer, time);
+	if (time_is_after_jiffies(time))
+		mod_timer(&own_query->timer, time);
 }

 static void
-- 
2.34.1