[syzbot] [ppp?] INFO: task hung in ppp_exit_net (4)

Hello,

syzbot found the following issue on:

HEAD commit:    2ef5971ff345 Merge tag 'vfs-6.10-rc4.fixes' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13e22cee980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b8786f381e62940f
dashboard link: https://syzkaller.appspot.com/bug?extid=32bd764abd98eb40dea8
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/db17be0247f3/disk-2ef5971f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/af92d227f130/vmlinux-2ef5971f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f98ae987ba14/bzImage-2ef5971f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]

INFO: task kworker/u8:4:61 blocked for more than 143 seconds.
      Not tainted 6.10.0-rc3-syzkaller-00021-g2ef5971ff345 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u8:4    state:D stack:22928 pid:61    tgid:61    ppid:2      flags:0x00004000
Workqueue: netns cleanup_net
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5408 [inline]
 __schedule+0xf15/0x5d00 kernel/sched/core.c:6745
 __schedule_loop kernel/sched/core.c:6822 [inline]
 schedule+0xe7/0x350 kernel/sched/core.c:6837
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6894
 __mutex_lock_common kernel/locking/mutex.c:684 [inline]
 __mutex_lock+0x5b8/0x9c0 kernel/locking/mutex.c:752
 ppp_exit_net+0xae/0x3b0 drivers/net/ppp/ppp_generic.c:1131
 ops_exit_list+0xb0/0x180 net/core/net_namespace.c:173
 cleanup_net+0x5b7/0xbf0 net/core/net_namespace.c:640
 process_one_work+0x9fb/0x1b60 kernel/workqueue.c:3231
 process_scheduled_works kernel/workqueue.c:3312 [inline]
 worker_thread+0x6c8/0xf70 kernel/workqueue.c:3393
 kthread+0x2c1/0x3a0 kernel/kthread.c:389
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
INFO: task syz-executor.2:8975 blocked for more than 143 seconds.
      Not tainted 6.10.0-rc3-syzkaller-00021-g2ef5971ff345 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor.2  state:D stack:26656 pid:8975  tgid:8973  ppid:5107   flags:0x00000006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5408 [inline]
 __schedule+0xf15/0x5d00 kernel/sched/core.c:6745
 __schedule_loop kernel/sched/core.c:6822 [inline]
 schedule+0xe7/0x350 kernel/sched/core.c:6837
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6894
 __mutex_lock_common kernel/locking/mutex.c:684 [inline]
 __mutex_lock+0x5b8/0x9c0 kernel/locking/mutex.c:752
 rtnl_lock net/core/rtnetlink.c:79 [inline]
 rtnetlink_rcv_msg+0x372/0xea0 net/core/rtnetlink.c:6632
 netlink_rcv_skb+0x16b/0x440 net/netlink/af_netlink.c:2564
 netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline]
 netlink_unicast+0x542/0x820 net/netlink/af_netlink.c:1361
 netlink_sendmsg+0x8b8/0xd70 net/netlink/af_netlink.c:1905
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg net/socket.c:745 [inline]
 ____sys_sendmsg+0xab5/0xc90 net/socket.c:2585
 ___sys_sendmsg+0x135/0x1e0 net/socket.c:2639
 __sys_sendmsg+0x117/0x1f0 net/socket.c:2668
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fcb2b07cea9
RSP: 002b:00007fcb2bead0c8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fcb2b1b3f80 RCX: 00007fcb2b07cea9
RDX: 0000000000000000 RSI: 0000000020000040 RDI: 0000000000000003
RBP: 00007fcb2b0ebff4 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007fcb2b1b3f80 R15: 00007ffcd9ec90f8
 </TASK>
INFO: task syz-executor.4:9029 blocked for more than 144 seconds.
      Not tainted 6.10.0-rc3-syzkaller-00021-g2ef5971ff345 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor.4  state:D stack:25968 pid:9029  tgid:9022  ppid:5111   flags:0x00004006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5408 [inline]
 __schedule+0xf15/0x5d00 kernel/sched/core.c:6745
 __schedule_loop kernel/sched/core.c:6822 [inline]
 schedule+0xe7/0x350 kernel/sched/core.c:6837
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6894
 __mutex_lock_common kernel/locking/mutex.c:684 [inline]
 __mutex_lock+0x5b8/0x9c0 kernel/locking/mutex.c:752
 register_nexthop_notifier+0x1b/0x70 net/ipv4/nexthop.c:3871
 ops_init+0xb9/0x650 net/core/net_namespace.c:139
 setup_net+0x435/0xb40 net/core/net_namespace.c:343
 copy_net_ns+0x2f0/0x670 net/core/net_namespace.c:508
 create_new_namespaces+0x3ea/0xb10 kernel/nsproxy.c:110
 unshare_nsproxy_namespaces+0xc0/0x1f0 kernel/nsproxy.c:228
 ksys_unshare+0x419/0x970 kernel/fork.c:3323
 __do_sys_unshare kernel/fork.c:3394 [inline]
 __se_sys_unshare kernel/fork.c:3392 [inline]
 __x64_sys_unshare+0x31/0x40 kernel/fork.c:3392
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9f8ae7cea9
RSP: 002b:00007f9f8bb220c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: ffffffffffffffda RBX: 00007f9f8afb4120 RCX: 00007f9f8ae7cea9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000064000600
RBP: 00007f9f8aeebff4 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000006e R14: 00007f9f8afb4120 R15: 00007ffd19e177f8
 </TASK>
INFO: task syz-executor.0:9026 blocked for more than 144 seconds.
      Not tainted 6.10.0-rc3-syzkaller-00021-g2ef5971ff345 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor.0  state:D stack:27968 pid:9026  tgid:9023  ppid:6840   flags:0x00004006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5408 [inline]
 __schedule+0xf15/0x5d00 kernel/sched/core.c:6745
 __schedule_loop kernel/sched/core.c:6822 [inline]
 schedule+0xe7/0x350 kernel/sched/core.c:6837
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6894
 __mutex_lock_common kernel/locking/mutex.c:684 [inline]
 __mutex_lock+0x5b8/0x9c0 kernel/locking/mutex.c:752


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