Re: Linux6.14-rc5 Bug: INFO: task hung in rtnl_dumpit

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: ffhgfv <xnxc22xnxc22@qq.com>
Date: Thu, 20 Mar 2025 08:26:01 -0400
> Hello, I found a bug titled "  INFO: task hung in rtnl_dumpit " with
> modified syzkaller in the Linux6.14-rc5.

Please stop sending task hung reports unless you have a repro.


> If you fix this issue, please add the following tag to the commit:
> Reported-by: Jianzhou Zhao <xnxc22xnxc22@qq.com>,    xingwei lee
> <xrivendell7@gmail.com>, Zhizhuo Tang <strforexctzzchange@foxmail.com>
> 
> I use the same kernel as syzbot instance upstream: 7eb172143d5508b4da468ed59ee857c6e5e01da6
> kernel config: https://syzkaller.appspot.com/text?tag=KernelConfig&amp;x=da4b04ae798b7ef6
> compiler: gcc version 11.4.0
> ------------[ cut here ]-----------------------------------------
>  TITLE:   INFO: task hung in rtnl_dumpit 
> ==================================================================
> INFO: task ifquery:17951 blocked for more than 143 seconds.
>       Not tainted 6.14.0-rc5-dirty #17

Also, please clarify what diff is applied on the upstream kernel.


> "echo 0 &gt; /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:ifquery         state:D stack:25008 pid:17951 tgid:17951 ppid:17950  task_flags:0x400000 flags:0x00000000
> Call Trace:
>  <task>
>  context_switch kernel/sched/core.c:5378 [inline]
>  __schedule+0x1074/0x4d30 kernel/sched/core.c:6765
>  __schedule_loop kernel/sched/core.c:6842 [inline]
>  schedule+0xd4/0x210 kernel/sched/core.c:6857
>  schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6914
>  __mutex_lock_common kernel/locking/mutex.c:662 [inline]
>  __mutex_lock+0x1042/0x2020 kernel/locking/mutex.c:730
>  rtnl_lock net/core/rtnetlink.c:79 [inline]

Even when you have a repro, if it's related to rtnl_lock() or its
family, please make sure it's NOT triggered by too many threads
trying to aquire to mutex.

For example, this report is a variant of one you sent few days ago,
and you can find many rtnl_dumpit() there too.

https://lore.kernel.org/netdev/tencent_A3FB41E607B2126D163C5D4C87DC196E0707@qq.com/

---8<---
INFO: task ifquery:17618 blocked for more than 145 seconds.
      Not tainted 6.14.0-rc5-dirty #11
"echo 0 &gt; /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:ifquery         state:D stack:22632 pid:17618 tgid:17618 ppid:17610  task_flags:0x400000 flags:0x00000000
Call Trace:
 <task>
 context_switch kernel/sched/core.c:5378 [inline]
 __schedule+0x1074/0x4d30 kernel/sched/core.c:6765
 __schedule_loop kernel/sched/core.c:6842 [inline]
 schedule+0xd4/0x210 kernel/sched/core.c:6857
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6914
 __mutex_lock_common kernel/locking/mutex.c:662 [inline]
 __mutex_lock+0x1042/0x2020 kernel/locking/mutex.c:730
 rtnl_lock net/core/rtnetlink.c:79 [inline]
 rtnl_dumpit+0x198/0x200 net/core/rtnetlink.c:6780
...
2 locks held by ifquery/17618:
 #0: ffff88800064a6c8 (nlk_cb_mutex-ROUTE){+.+.}-{4:4}, at: netlink_dump+0x6f3/0xc80 net/netlink/af_netlink.c:2254
 #1: ffffffff8fee5d68 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:79 [inline]
 #1: ffffffff8fee5d68 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_dumpit+0x198/0x200 net/core/rtnetlink.c:6780
2 locks held by syz-executor/17625:
 #0: ffffffff8fecfdd0 (pernet_ops_rwsem){++++}-{4:4}, at: copy_net_ns+0x2c3/0x640 net/core/net_namespace.c:512
 #1: ffffffff8fee5d68 (rtnl_mutex){+.+.}-{4:4}, at: ip_tunnel_init_net+0x30c/0xb10 net/ipv4/ip_tunnel.c:1159
2 locks held by ifquery/17649:
 #0: ffff88805d5fc6c8 (nlk_cb_mutex-ROUTE){+.+.}-{4:4}, at: netlink_dump+0x6f3/0xc80 net/netlink/af_netlink.c:2254
 #1: ffffffff8fee5d68 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:79 [inline]
 #1: ffffffff8fee5d68 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_dumpit+0x198/0x200 net/core/rtnetlink.c:6780
1 lock held by systemd-rfkill/17664:
 #0: ffff888045e80f88 (mapping.invalidate_lock){++++}-{4:4}, at: filemap_invalidate_lock_shared include/linux/fs.h:932 [inline]
 #0: ffff888045e80f88 (mapping.invalidate_lock){++++}-{4:4}, at: filemap_fault+0xed2/0x2650 mm/filemap.c:3435
2 locks held by ifquery/17698:
 #0: ffff8880417046c8 (nlk_cb_mutex-ROUTE){+.+.}-{4:4}, at: netlink_dump+0x6f3/0xc80 net/netlink/af_netlink.c:2254
 #1: ffffffff8fee5d68 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:79 [inline]
 #1: ffffffff8fee5d68 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_dumpit+0x198/0x200 net/core/rtnetlink.c:6780
---8<---