Re: [PATCH net v2] net: bridge: fix soft lockup in br_multicast_query_expired()

[Wang Liang <wangliang74@huawei.com>]

在 2025/8/12 14:10, Ido Schimmel 写道:
> On Tue, Aug 12, 2025 at 05:18:18PM +0800, Wang Liang wrote:
>> 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
>>
>> The multicast_startup_query_interval can also cause this issue. Similar to
>> the commit 99b40610956a("net: bridge: mcast: add and enforce query interval
>                           ^ missing space
>
>> minimum"), add check for the query interval maximum to fix this issue.
>>
>> Link: https://lore.kernel.org/netdev/20250806094941.1285944-1-wangliang74@huawei.com/
>> Fixes: 7e4df51eb35d ("bridge: netlink: add support for igmp's intervals")
> Probably doesn't matter in practice given how old both commits are, but
> I think you should blame d902eee43f19 ("bridge: Add multicast
> count/interval sysfs entries") instead. The commit message also uses the
> sysfs path and not the netlink one.


Thanks for your suggestions!

The bug fix tag is really important. I will correct it and send a new 
patch later.

>> Suggested-by: Nikolay Aleksandrov <razor@blackwall.org>
>> Signed-off-by: Wang Liang <wangliang74@huawei.com>
> Code looks fine to me.