Re: net: deadlock on genl_mutex

From: Dmitry Vyukov
Date: Thu Dec 08 2016 - 13:02:46 EST

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On Thu, Dec 8, 2016 at 6:16 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> On Thu, Dec 8, 2016 at 5:16 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>> On Tue, Nov 29, 2016 at 6:59 AM, <subashab@xxxxxxxxxxxxxx> wrote:
>>>>
>>>> Issue was reported yesterday and is under investigation.
>>>>
>>>>
>>>> http://marc.info/?l=linux-netdev&m=148014004331663&w=2
>>>>
>>>>
>>>> Thanks !
>>>
>>>
>>> Hi Dmitry
>>>
>>> Can you try the patch below with your reproducer? I haven't seen similar
>>> crashes reported after this (or even with Eric's patch).
>>
>> I've synced to 318c8932ddec5c1c26a4af0f3c053784841c598e (Dec 7) and do
>> _not_ see this report happening anymore.
>> Thanks.
>
>
> But now I am seeing "possible deadlock" warnings involving genl_lock:
>
> [ INFO: possible circular locking dependency detected ]
> 4.9.0-rc8+ #77 Not tainted
> -------------------------------------------------------
> syz-executor7/18794 is trying to acquire lock:
> (rtnl_mutex){+.+.+.}, at: [<ffffffff86b4682c>] rtnl_lock+0x1c/0x20
> net/core/rtnetlink.c:70
> but task is already holding lock:
> (genl_mutex){+.+.+.}, at: [< inline >] genl_lock
> net/netlink/genetlink.c:31
> (genl_mutex){+.+.+.}, at: [<ffffffff86cc27c9>]
> genl_rcv_msg+0x209/0x260 net/netlink/genetlink.c:658
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> [ 315.403815] [< inline >] validate_chain
> kernel/locking/lockdep.c:2265
> [ 315.403815] [<ffffffff81569576>]
> __lock_acquire+0x2156/0x3380 kernel/locking/lockdep.c:3338
> [ 315.403815] [<ffffffff8156b672>] lock_acquire+0x2a2/0x790
> kernel/locking/lockdep.c:3749
> [ 315.403815] [< inline >] __mutex_lock_common
> kernel/locking/mutex.c:521
> [ 315.403815] [<ffffffff88195bcf>]
> mutex_lock_nested+0x23f/0xf20 kernel/locking/mutex.c:621
> [ 315.403815] [< inline >] genl_lock net/netlink/genetlink.c:31
> [ 315.403815] [<ffffffff86cc0c26>] genl_lock_dumpit+0x46/0xa0
> net/netlink/genetlink.c:518
> [ 315.403815] [<ffffffff86cb33ac>] netlink_dump+0x57c/0xd70
> net/netlink/af_netlink.c:2127
> [ 315.403815] [<ffffffff86cb7b6a>]
> __netlink_dump_start+0x4ea/0x760 net/netlink/af_netlink.c:2217
> [ 315.403815] [<ffffffff86cc2319>]
> genl_family_rcv_msg+0xdc9/0x1070 net/netlink/genetlink.c:586
> [ 315.403815] [<ffffffff86cc2770>] genl_rcv_msg+0x1b0/0x260
> net/netlink/genetlink.c:660
> [ 315.403815] [<ffffffff86cc034c>] netlink_rcv_skb+0x2bc/0x3a0
> net/netlink/af_netlink.c:2298
> [ 315.403815] [<ffffffff86cc153d>] genl_rcv+0x2d/0x40
> net/netlink/genetlink.c:671
> [ 315.403815] [< inline >] netlink_unicast_kernel
> net/netlink/af_netlink.c:1231
> [ 315.403815] [<ffffffff86cbeb6a>] netlink_unicast+0x51a/0x740
> net/netlink/af_netlink.c:1257
> [ 315.403815] [<ffffffff86cbf834>] netlink_sendmsg+0xaa4/0xe50
> net/netlink/af_netlink.c:1803
> [ 315.403815] [< inline >] sock_sendmsg_nosec net/socket.c:621
> [ 315.403815] [<ffffffff86a7618f>] sock_sendmsg+0xcf/0x110
> net/socket.c:631
> [ 315.403815] [<ffffffff86a764fb>] sock_write_iter+0x32b/0x620
> net/socket.c:829
> [ 315.403815] [< inline >] new_sync_write fs/read_write.c:499
> [ 315.403815] [<ffffffff81a701ae>] __vfs_write+0x4fe/0x830
> fs/read_write.c:512
> [ 315.403815] [<ffffffff81a71c55>] vfs_write+0x175/0x4e0
> fs/read_write.c:560
> [ 315.403815] [< inline >] SYSC_write fs/read_write.c:607
> [ 315.403815] [<ffffffff81a760e0>] SyS_write+0x100/0x240
> fs/read_write.c:599
> [ 315.403815] [<ffffffff881a5f85>] entry_SYSCALL_64_fastpath+0x23/0xc6
>
> [ 315.403815] [< inline >] validate_chain
> kernel/locking/lockdep.c:2265
> [ 315.403815] [<ffffffff81569576>]
> __lock_acquire+0x2156/0x3380 kernel/locking/lockdep.c:3338
> [ 315.403815] [<ffffffff8156b672>] lock_acquire+0x2a2/0x790
> kernel/locking/lockdep.c:3749
> [ 315.403815] [< inline >] __mutex_lock_common
> kernel/locking/mutex.c:521
> [ 315.403815] [<ffffffff88195bcf>]
> mutex_lock_nested+0x23f/0xf20 kernel/locking/mutex.c:621
> [ 315.403815] [<ffffffff86cb7779>]
> __netlink_dump_start+0xf9/0x760 net/netlink/af_netlink.c:2187
> [ 315.403815] [< inline >] netlink_dump_start
> include/linux/netlink.h:165
> [ 315.403815] [<ffffffff86d14d48>]
> ctnetlink_stat_ct_cpu+0x198/0x1e0
> net/netfilter/nf_conntrack_netlink.c:2045
> [ 315.403815] [<ffffffff86cd313e>]
> nfnetlink_rcv_msg+0x9be/0xd60 net/netfilter/nfnetlink.c:212
> [ 315.403815] [<ffffffff86cc034c>] netlink_rcv_skb+0x2bc/0x3a0
> net/netlink/af_netlink.c:2298
> [ 315.403815] [<ffffffff86cd1b71>] nfnetlink_rcv+0x7e1/0x10d0
> net/netfilter/nfnetlink.c:474
> [ 315.403815] [< inline >] netlink_unicast_kernel
> net/netlink/af_netlink.c:1231
> [ 315.403815] [<ffffffff86cbeb6a>] netlink_unicast+0x51a/0x740
> net/netlink/af_netlink.c:1257
> [ 315.403815] [<ffffffff86cbf834>] netlink_sendmsg+0xaa4/0xe50
> net/netlink/af_netlink.c:1803
> [ 315.403815] [< inline >] sock_sendmsg_nosec net/socket.c:621
> [ 315.403815] [<ffffffff86a7618f>] sock_sendmsg+0xcf/0x110
> net/socket.c:631
> [ 315.403815] [<ffffffff86a764fb>] sock_write_iter+0x32b/0x620
> net/socket.c:829
> [ 315.403815] [< inline >] new_sync_write fs/read_write.c:499
> [ 315.403815] [<ffffffff81a701ae>] __vfs_write+0x4fe/0x830
> fs/read_write.c:512
> [ 315.403815] [<ffffffff81a71c55>] vfs_write+0x175/0x4e0
> fs/read_write.c:560
> [ 315.403815] [< inline >] SYSC_write fs/read_write.c:607
> [ 315.403815] [<ffffffff81a760e0>] SyS_write+0x100/0x240
> fs/read_write.c:599
> [ 315.403815] [<ffffffff881a5f85>] entry_SYSCALL_64_fastpath+0x23/0xc6
>
> [ 315.403815] [< inline >] validate_chain
> kernel/locking/lockdep.c:2265
> [ 315.403815] [<ffffffff81569576>]
> __lock_acquire+0x2156/0x3380 kernel/locking/lockdep.c:3338
> [ 315.403815] [<ffffffff8156b672>] lock_acquire+0x2a2/0x790
> kernel/locking/lockdep.c:3749
> [ 315.403815] [< inline >] __mutex_lock_common
> kernel/locking/mutex.c:521
> [ 315.403815] [<ffffffff88195bcf>]
> mutex_lock_nested+0x23f/0xf20 kernel/locking/mutex.c:621
> [ 315.403815] [<ffffffff86cd083d>] nfnl_lock+0x2d/0x30
> net/netfilter/nfnetlink.c:61
> [ 315.403815] [<ffffffff86d7c5b1>]
> nf_tables_netdev_event+0x1f1/0x720
> net/netfilter/nf_tables_netdev.c:122
> [ 315.403815] [<ffffffff8149095a>]
> notifier_call_chain+0x14a/0x2f0 kernel/notifier.c:93
> [ 315.403815] [< inline >] __raw_notifier_call_chain
> kernel/notifier.c:394
> [ 315.403815] [<ffffffff81490b82>]
> raw_notifier_call_chain+0x32/0x40 kernel/notifier.c:401
> [ 315.403815] [<ffffffff86ae4af6>]
> call_netdevice_notifiers_info+0x56/0x90 net/core/dev.c:1645
> [ 315.403815] [< inline >] call_netdevice_notifiers
> net/core/dev.c:1661
> [ 315.403815] [<ffffffff86af898d>]
> rollback_registered_many+0x73d/0xba0 net/core/dev.c:6759
> [ 315.403815] [<ffffffff86af8e9e>]
> rollback_registered+0xae/0x100 net/core/dev.c:6800
> [ 315.403815] [<ffffffff86af8f76>]
> unregister_netdevice_queue+0x86/0x140 net/core/dev.c:7787
> [ 315.403815] [< inline >] unregister_netdevice
> include/linux/netdevice.h:2455
> [ 315.403815] [<ffffffff84912be6>] __tun_detach+0xc66/0xea0
> drivers/net/tun.c:567
> [ 315.808015] [< inline >] tun_detach drivers/net/tun.c:578
> [ 315.808015] [<ffffffff84912e69>] tun_chr_close+0x49/0x60
> drivers/net/tun.c:2350
> [ 315.808015] [<ffffffff81a77f7e>] __fput+0x34e/0x910
> fs/file_table.c:208
> [ 315.808015] [<ffffffff81a785ca>] ____fput+0x1a/0x20
> fs/file_table.c:244
> [ 315.808015] [<ffffffff81483c20>] task_work_run+0x1a0/0x280
> kernel/task_work.c:116
> [ 315.808015] [< inline >] exit_task_work
> include/linux/task_work.h:21
> [ 315.808015] [<ffffffff814129e2>] do_exit+0x1842/0x2650
> kernel/exit.c:828
> [ 315.808015] [<ffffffff814139ae>] do_group_exit+0x14e/0x420
> kernel/exit.c:932
> [ 315.808015] [<ffffffff81442b43>] get_signal+0x663/0x1880
> kernel/signal.c:2307
> [ 315.808015] [<ffffffff81239b45>] do_signal+0xc5/0x2190
> arch/x86/kernel/signal.c:807
> [ 315.808015] [<ffffffff8100666a>]
> exit_to_usermode_loop+0x1ea/0x2d0 arch/x86/entry/common.c:156
> [ 315.808015] [< inline >] prepare_exit_to_usermode
> arch/x86/entry/common.c:190
> [ 315.808015] [<ffffffff81009693>]
> syscall_return_slowpath+0x4d3/0x570 arch/x86/entry/common.c:259
> [ 315.808015] [<ffffffff881a6026>] entry_SYSCALL_64_fastpath+0xc4/0xc6
>
> [ 315.808015] [< inline >] check_prev_add
> kernel/locking/lockdep.c:1828
> [ 315.808015] [<ffffffff8156309b>]
> check_prevs_add+0xaab/0x1c20 kernel/locking/lockdep.c:1938
> [ 315.808015] [< inline >] validate_chain
> kernel/locking/lockdep.c:2265
> [ 315.808015] [<ffffffff81569576>]
> __lock_acquire+0x2156/0x3380 kernel/locking/lockdep.c:3338
> [ 315.808015] [<ffffffff8156b672>] lock_acquire+0x2a2/0x790
> kernel/locking/lockdep.c:3749
> [ 315.808015] [< inline >] __mutex_lock_common
> kernel/locking/mutex.c:521
> [ 315.808015] [<ffffffff88195bcf>]
> mutex_lock_nested+0x23f/0xf20 kernel/locking/mutex.c:621
> [ 315.808015] [<ffffffff86b4682c>] rtnl_lock+0x1c/0x20
> net/core/rtnetlink.c:70
> [ 315.808015] [<ffffffff87b5cdf9>]
> nl80211_pre_doit+0x309/0x5b0 net/wireless/nl80211.c:11750
> [ 315.808015] [<ffffffff86cc1cd0>]
> genl_family_rcv_msg+0x780/0x1070 net/netlink/genetlink.c:631
> [ 315.808015] [<ffffffff86cc2770>] genl_rcv_msg+0x1b0/0x260
> net/netlink/genetlink.c:660
> [ 315.808015] [<ffffffff86cc034c>] netlink_rcv_skb+0x2bc/0x3a0
> net/netlink/af_netlink.c:2298
> [ 315.808015] [<ffffffff86cc153d>] genl_rcv+0x2d/0x40
> net/netlink/genetlink.c:671
> [ 315.808015] [< inline >] netlink_unicast_kernel
> net/netlink/af_netlink.c:1231
> [ 315.808015] [<ffffffff86cbeb6a>] netlink_unicast+0x51a/0x740
> net/netlink/af_netlink.c:1257
> [ 315.808015] [<ffffffff86cbf834>] netlink_sendmsg+0xaa4/0xe50
> net/netlink/af_netlink.c:1803
> [ 315.808015] [< inline >] sock_sendmsg_nosec net/socket.c:621
> [ 315.808015] [<ffffffff86a7618f>] sock_sendmsg+0xcf/0x110
> net/socket.c:631
> [ 315.808015] [<ffffffff86a764fb>] sock_write_iter+0x32b/0x620
> net/socket.c:829
> [ 315.808015] [<ffffffff81a6f9a3>]
> do_iter_readv_writev+0x363/0x670 fs/read_write.c:695
> [ 315.808015] [<ffffffff81a723f1>] do_readv_writev+0x431/0x9b0
> fs/read_write.c:872
> [ 315.808015] [<ffffffff81a72f2c>] vfs_writev+0x8c/0xc0
> fs/read_write.c:911
> [ 315.808015] [<ffffffff81a73075>] do_writev+0x115/0x2d0
> fs/read_write.c:944
> [ 315.808015] [< inline >] SYSC_writev fs/read_write.c:1017
> [ 315.808015] [<ffffffff81a7682c>] SyS_writev+0x2c/0x40
> fs/read_write.c:1014
> [ 315.808015] [<ffffffff881a5f85>] entry_SYSCALL_64_fastpath+0x23/0xc6
>
> other info that might help us debug this:
>
> Chain exists of:
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(genl_mutex);
> lock(nlk->cb_mutex);
> lock(genl_mutex);
> lock(rtnl_mutex);
>
> *** DEADLOCK ***
>
> 2 locks held by syz-executor7/18794:
> #0: (cb_lock){++++++}, at: [<ffffffff86cc152e>] genl_rcv+0x1e/0x40
> net/netlink/genetlink.c:670
> #1: (genl_mutex){+.+.+.}, at: [< inline >] genl_lock
> net/netlink/genetlink.c:31
> #1: (genl_mutex){+.+.+.}, at: [<ffffffff86cc27c9>]
> genl_rcv_msg+0x209/0x260 net/netlink/genetlink.c:658
>
> stack backtrace:
> CPU: 0 PID: 18794 Comm: syz-executor7 Not tainted 4.9.0-rc8+ #77
> Hardware name: Google Google/Google, BIOS Google 01/01/2011
> ffff88004add6468 ffffffff834c44f9 ffffffff00000000 1ffff100095bac20
> ffffed00095bac18 0000000041b58ab3 ffffffff895816f0 ffffffff834c420b
> 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> Call Trace:
> [< inline >] __dump_stack lib/dump_stack.c:15
> [<ffffffff834c44f9>] dump_stack+0x2ee/0x3f5 lib/dump_stack.c:51
> [<ffffffff81560cb0>] print_circular_bug+0x310/0x3c0
> kernel/locking/lockdep.c:1202
> [< inline >] check_prev_add kernel/locking/lockdep.c:1828
> [<ffffffff8156309b>] check_prevs_add+0xaab/0x1c20 kernel/locking/lockdep.c:1938
> [< inline >] validate_chain kernel/locking/lockdep.c:2265
> [<ffffffff81569576>] __lock_acquire+0x2156/0x3380 kernel/locking/lockdep.c:3338
> [<ffffffff8156b672>] lock_acquire+0x2a2/0x790 kernel/locking/lockdep.c:3749
> [< inline >] __mutex_lock_common kernel/locking/mutex.c:521
> [<ffffffff88195bcf>] mutex_lock_nested+0x23f/0xf20 kernel/locking/mutex.c:621
> [<ffffffff86b4682c>] rtnl_lock+0x1c/0x20 net/core/rtnetlink.c:70
> [<ffffffff87b5cdf9>] nl80211_pre_doit+0x309/0x5b0 net/wireless/nl80211.c:11750
> [<ffffffff86cc1cd0>] genl_family_rcv_msg+0x780/0x1070
> net/netlink/genetlink.c:631
> [<ffffffff86cc2770>] genl_rcv_msg+0x1b0/0x260 net/netlink/genetlink.c:660
> [<ffffffff86cc034c>] netlink_rcv_skb+0x2bc/0x3a0 net/netlink/af_netlink.c:2298
> [<ffffffff86cc153d>] genl_rcv+0x2d/0x40 net/netlink/genetlink.c:671
> [< inline >] netlink_unicast_kernel net/netlink/af_netlink.c:1231
> [<ffffffff86cbeb6a>] netlink_unicast+0x51a/0x740 net/netlink/af_netlink.c:1257
> [<ffffffff86cbf834>] netlink_sendmsg+0xaa4/0xe50 net/netlink/af_netlink.c:1803
> [< inline >] sock_sendmsg_nosec net/socket.c:621
> [<ffffffff86a7618f>] sock_sendmsg+0xcf/0x110 net/socket.c:631
> [<ffffffff86a764fb>] sock_write_iter+0x32b/0x620 net/socket.c:829
> [<ffffffff81a6f9a3>] do_iter_readv_writev+0x363/0x670 fs/read_write.c:695
> [<ffffffff81a723f1>] do_readv_writev+0x431/0x9b0 fs/read_write.c:872
> [<ffffffff81a72f2c>] vfs_writev+0x8c/0xc0 fs/read_write.c:911
> [<ffffffff81a73075>] do_writev+0x115/0x2d0 fs/read_write.c:944
> [< inline >] SYSC_writev fs/read_write.c:1017
> [<ffffffff81a7682c>] SyS_writev+0x2c/0x40 fs/read_write.c:1014
> [<ffffffff881a5f85>] entry_SYSCALL_64_fastpath+0x23/0xc6

Probably a related one:

[ INFO: possible circular locking dependency detected ]
4.9.0-rc8+ #77 Not tainted
-------------------------------------------------------
syz-executor5/5777 is trying to acquire lock:
(genl_mutex){+.+.+.}, at: [< inline >] genl_lock
net/netlink/genetlink.c:31
(genl_mutex){+.+.+.}, at: [<ffffffff86cc0c26>]
genl_lock_dumpit+0x46/0xa0 net/netlink/genetlink.c:518
but task is already holding lock:
(nlk->cb_mutex){+.+.+.}, at: [<ffffffff86cb2f08>]
netlink_dump+0xd8/0xd70 net/netlink/af_netlink.c:2084
which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

[ 158.966653] [< inline >] validate_chain
kernel/locking/lockdep.c:2265
[ 158.966653] [<ffffffff81569576>]
__lock_acquire+0x2156/0x3380 kernel/locking/lockdep.c:3338
[ 158.966653] [<ffffffff8156b672>] lock_acquire+0x2a2/0x790
kernel/locking/lockdep.c:3749
[ 158.966653] [< inline >] __mutex_lock_common
kernel/locking/mutex.c:521
[ 158.966653] [<ffffffff88195bcf>]
mutex_lock_nested+0x23f/0xf20 kernel/locking/mutex.c:621
[ 158.966653] [<ffffffff86cb7779>]
__netlink_dump_start+0xf9/0x760 net/netlink/af_netlink.c:2187
[ 158.966653] [< inline >] netlink_dump_start
include/linux/netlink.h:165
[ 158.966653] [<ffffffff86d1395f>]
ctnetlink_get_ct_unconfirmed+0x17f/0x220
net/netfilter/nf_conntrack_netlink.c:1369
[ 158.966653] [<ffffffff86cd313e>]
nfnetlink_rcv_msg+0x9be/0xd60 net/netfilter/nfnetlink.c:212
[ 158.966653] [<ffffffff86cc034c>] netlink_rcv_skb+0x2bc/0x3a0
net/netlink/af_netlink.c:2298
[ 158.966653] [<ffffffff86cd1b71>] nfnetlink_rcv+0x7e1/0x10d0
net/netfilter/nfnetlink.c:474
[ 158.966653] [< inline >] netlink_unicast_kernel
net/netlink/af_netlink.c:1231
[ 158.966653] [<ffffffff86cbeb6a>] netlink_unicast+0x51a/0x740
net/netlink/af_netlink.c:1257
[ 158.966653] [<ffffffff86cbf834>] netlink_sendmsg+0xaa4/0xe50
net/netlink/af_netlink.c:1803
[ 158.966653] [< inline >] sock_sendmsg_nosec net/socket.c:621
[ 158.966653] [<ffffffff86a7618f>] sock_sendmsg+0xcf/0x110
net/socket.c:631
[ 158.966653] [<ffffffff86a764fb>] sock_write_iter+0x32b/0x620
net/socket.c:829
[ 158.966653] [< inline >] new_sync_write fs/read_write.c:499
[ 158.966653] [<ffffffff81a701ae>] __vfs_write+0x4fe/0x830
fs/read_write.c:512
[ 158.966653] [<ffffffff81a71c55>] vfs_write+0x175/0x4e0
fs/read_write.c:560
[ 158.966653] [< inline >] SYSC_write fs/read_write.c:607
[ 158.966653] [<ffffffff81a760e0>] SyS_write+0x100/0x240
fs/read_write.c:599
[ 158.966653] [<ffffffff881a5f85>] entry_SYSCALL_64_fastpath+0x23/0xc6

[ 158.966653] [< inline >] validate_chain
kernel/locking/lockdep.c:2265
[ 158.966653] [<ffffffff81569576>]
__lock_acquire+0x2156/0x3380 kernel/locking/lockdep.c:3338
[ 158.966653] [<ffffffff8156b672>] lock_acquire+0x2a2/0x790
kernel/locking/lockdep.c:3749
[ 158.966653] [< inline >] __mutex_lock_common
kernel/locking/mutex.c:521
[ 158.966653] [<ffffffff88195bcf>]
mutex_lock_nested+0x23f/0xf20 kernel/locking/mutex.c:621
[ 158.966653] [<ffffffff86cd083d>] nfnl_lock+0x2d/0x30
net/netfilter/nfnetlink.c:61
[ 158.966653] [<ffffffff86d7c5b1>]
nf_tables_netdev_event+0x1f1/0x720
net/netfilter/nf_tables_netdev.c:122
[ 158.966653] [<ffffffff8149095a>]
notifier_call_chain+0x14a/0x2f0 kernel/notifier.c:93
[ 158.966653] [< inline >] __raw_notifier_call_chain
kernel/notifier.c:394
[ 158.966653] [<ffffffff81490b82>]
raw_notifier_call_chain+0x32/0x40 kernel/notifier.c:401
[ 158.966653] [<ffffffff86ae4af6>]
call_netdevice_notifiers_info+0x56/0x90 net/core/dev.c:1645
[ 158.966653] [< inline >] call_netdevice_notifiers
net/core/dev.c:1661
[ 158.966653] [<ffffffff86af898d>]
rollback_registered_many+0x73d/0xba0 net/core/dev.c:6759
[ 158.966653] [<ffffffff86af8e9e>]
rollback_registered+0xae/0x100 net/core/dev.c:6800
[ 158.966653] [<ffffffff86af8f76>]
unregister_netdevice_queue+0x86/0x140 net/core/dev.c:7787
[ 158.966653] [< inline >] unregister_netdevice
include/linux/netdevice.h:2455
[ 158.966653] [<ffffffff84912be6>] __tun_detach+0xc66/0xea0
drivers/net/tun.c:567
[ 158.966653] [< inline >] tun_detach drivers/net/tun.c:578
[ 158.966653] [<ffffffff84912e69>] tun_chr_close+0x49/0x60
drivers/net/tun.c:2350
[ 158.966653] [<ffffffff81a77f7e>] __fput+0x34e/0x910
fs/file_table.c:208
[ 158.966653] [<ffffffff81a785ca>] ____fput+0x1a/0x20
fs/file_table.c:244
[ 158.966653] [<ffffffff81483c20>] task_work_run+0x1a0/0x280
kernel/task_work.c:116
[ 158.966653] [< inline >] exit_task_work
include/linux/task_work.h:21
[ 158.966653] [<ffffffff814129e2>] do_exit+0x1842/0x2650
kernel/exit.c:828
[ 158.966653] [<ffffffff814139ae>] do_group_exit+0x14e/0x420
kernel/exit.c:932
[ 159.308048] [<ffffffff81442b43>] get_signal+0x663/0x1880
kernel/signal.c:2307
[ 159.308048] [<ffffffff81239b45>] do_signal+0xc5/0x2190
arch/x86/kernel/signal.c:807
[ 159.308048] [<ffffffff8100666a>]
exit_to_usermode_loop+0x1ea/0x2d0 arch/x86/entry/common.c:156
[ 159.308048] [< inline >] prepare_exit_to_usermode
arch/x86/entry/common.c:190
[ 159.308048] [<ffffffff81009693>]
syscall_return_slowpath+0x4d3/0x570 arch/x86/entry/common.c:259
[ 159.308048] [<ffffffff881a6026>] entry_SYSCALL_64_fastpath+0xc4/0xc6

[ 159.308048] [< inline >] validate_chain
kernel/locking/lockdep.c:2265
[ 159.308048] [<ffffffff81569576>]
__lock_acquire+0x2156/0x3380 kernel/locking/lockdep.c:3338
[ 159.308048] [<ffffffff8156b672>] lock_acquire+0x2a2/0x790
kernel/locking/lockdep.c:3749
[ 159.308048] [< inline >] __mutex_lock_common
kernel/locking/mutex.c:521
[ 159.308048] [<ffffffff88195bcf>]
mutex_lock_nested+0x23f/0xf20 kernel/locking/mutex.c:621
[ 159.308048] [<ffffffff86b4682c>] rtnl_lock+0x1c/0x20
net/core/rtnetlink.c:70
[ 159.308048] [<ffffffff87b5cdf9>]
nl80211_pre_doit+0x309/0x5b0 net/wireless/nl80211.c:11750
[ 159.308048] [<ffffffff86cc1cd0>]
genl_family_rcv_msg+0x780/0x1070 net/netlink/genetlink.c:631
[ 159.308048] [<ffffffff86cc2770>] genl_rcv_msg+0x1b0/0x260
net/netlink/genetlink.c:660
[ 159.308048] [<ffffffff86cc034c>] netlink_rcv_skb+0x2bc/0x3a0
net/netlink/af_netlink.c:2298
[ 159.308048] [<ffffffff86cc153d>] genl_rcv+0x2d/0x40
net/netlink/genetlink.c:671
[ 159.308048] [< inline >] netlink_unicast_kernel
net/netlink/af_netlink.c:1231
[ 159.308048] [<ffffffff86cbeb6a>] netlink_unicast+0x51a/0x740
net/netlink/af_netlink.c:1257
[ 159.308048] [<ffffffff86cbf834>] netlink_sendmsg+0xaa4/0xe50
net/netlink/af_netlink.c:1803
[ 159.308048] [< inline >] sock_sendmsg_nosec net/socket.c:621
[ 159.308048] [<ffffffff86a7618f>] sock_sendmsg+0xcf/0x110
net/socket.c:631
[ 159.308048] [<ffffffff86a764fb>] sock_write_iter+0x32b/0x620
net/socket.c:829
[ 159.308048] [<ffffffff81a6f9a3>]
do_iter_readv_writev+0x363/0x670 fs/read_write.c:695
[ 159.308048] [<ffffffff81a723f1>] do_readv_writev+0x431/0x9b0
fs/read_write.c:872
[ 159.308048] [<ffffffff81a72f2c>] vfs_writev+0x8c/0xc0
fs/read_write.c:911
[ 159.308048] [<ffffffff81a73075>] do_writev+0x115/0x2d0
fs/read_write.c:944
[ 159.308048] [< inline >] SYSC_writev fs/read_write.c:1017
[ 159.308048] [<ffffffff81a7682c>] SyS_writev+0x2c/0x40
fs/read_write.c:1014
[ 159.308048] [<ffffffff881a5f85>] entry_SYSCALL_64_fastpath+0x23/0xc6

[ 159.308048] [< inline >] check_prev_add
kernel/locking/lockdep.c:1828
[ 159.308048] [<ffffffff8156309b>]
check_prevs_add+0xaab/0x1c20 kernel/locking/lockdep.c:1938
[ 159.308048] [< inline >] validate_chain
kernel/locking/lockdep.c:2265
[ 159.308048] [<ffffffff81569576>]
__lock_acquire+0x2156/0x3380 kernel/locking/lockdep.c:3338
[ 159.308048] [<ffffffff8156b672>] lock_acquire+0x2a2/0x790
kernel/locking/lockdep.c:3749
[ 159.308048] [< inline >] __mutex_lock_common
kernel/locking/mutex.c:521
[ 159.308048] [<ffffffff88195bcf>]
mutex_lock_nested+0x23f/0xf20 kernel/locking/mutex.c:621
[ 159.308048] [< inline >] genl_lock net/netlink/genetlink.c:31
[ 159.308048] [<ffffffff86cc0c26>] genl_lock_dumpit+0x46/0xa0
net/netlink/genetlink.c:518
[ 159.308048] [<ffffffff86cb33ac>] netlink_dump+0x57c/0xd70
net/netlink/af_netlink.c:2127
[ 159.308048] [<ffffffff86cb7b6a>]
__netlink_dump_start+0x4ea/0x760 net/netlink/af_netlink.c:2217
[ 159.308048] [<ffffffff86cc2319>]
genl_family_rcv_msg+0xdc9/0x1070 net/netlink/genetlink.c:586
[ 159.308048] [<ffffffff86cc2770>] genl_rcv_msg+0x1b0/0x260
net/netlink/genetlink.c:660
[ 159.308048] [<ffffffff86cc034c>] netlink_rcv_skb+0x2bc/0x3a0
net/netlink/af_netlink.c:2298
[ 159.308048] [<ffffffff86cc153d>] genl_rcv+0x2d/0x40
net/netlink/genetlink.c:671
[ 159.308048] [< inline >] netlink_unicast_kernel
net/netlink/af_netlink.c:1231
[ 159.308048] [<ffffffff86cbeb6a>] netlink_unicast+0x51a/0x740
net/netlink/af_netlink.c:1257
[ 159.308048] [<ffffffff86cbf834>] netlink_sendmsg+0xaa4/0xe50
net/netlink/af_netlink.c:1803
[ 159.308048] [< inline >] sock_sendmsg_nosec net/socket.c:621
[ 159.308048] [<ffffffff86a7618f>] sock_sendmsg+0xcf/0x110
net/socket.c:631
[ 159.308048] [<ffffffff86a764fb>] sock_write_iter+0x32b/0x620
net/socket.c:829
[ 159.308048] [< inline >] new_sync_write fs/read_write.c:499
[ 159.308048] [<ffffffff81a701ae>] __vfs_write+0x4fe/0x830
fs/read_write.c:512
[ 159.308048] [<ffffffff81a71c55>] vfs_write+0x175/0x4e0
fs/read_write.c:560
[ 159.308048] [< inline >] SYSC_write fs/read_write.c:607
[ 159.308048] [<ffffffff81a760e0>] SyS_write+0x100/0x240
fs/read_write.c:599
[ 159.308048] [<ffffffff881a5f85>] entry_SYSCALL_64_fastpath+0x23/0xc6

other info that might help us debug this:

Chain exists of:
Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(nlk->cb_mutex);
lock(&table[i].mutex);
lock(nlk->cb_mutex);
lock(genl_mutex);

*** DEADLOCK ***

2 locks held by syz-executor5/5777:
#0: (cb_lock){++++++}, at: [<ffffffff86cc152e>] genl_rcv+0x1e/0x40
net/netlink/genetlink.c:670
#1: (nlk->cb_mutex){+.+.+.}, at: [<ffffffff86cb2f08>]
netlink_dump+0xd8/0xd70 net/netlink/af_netlink.c:2084

stack backtrace:
CPU: 1 PID: 5777 Comm: syz-executor5 Not tainted 4.9.0-rc8+ #77
Hardware name: Google Google/Google, BIOS Google 01/01/2011
ffff88005fe363e8 ffffffff834c44f9 ffffffff00000001 1ffff1000bfc6c10
ffffed000bfc6c08 0000000041b58ab3 ffffffff895816f0 ffffffff834c420b
0000000000000000 0000000000000000 0000000000000000 dffffc0000000000
Call Trace:
[< inline >] __dump_stack lib/dump_stack.c:15
[<ffffffff834c44f9>] dump_stack+0x2ee/0x3f5 lib/dump_stack.c:51
[<ffffffff81560cb0>] print_circular_bug+0x310/0x3c0
kernel/locking/lockdep.c:1202
[< inline >] check_prev_add kernel/locking/lockdep.c:1828
[<ffffffff8156309b>] check_prevs_add+0xaab/0x1c20 kernel/locking/lockdep.c:1938
[< inline >] validate_chain kernel/locking/lockdep.c:2265
[<ffffffff81569576>] __lock_acquire+0x2156/0x3380 kernel/locking/lockdep.c:3338
[<ffffffff8156b672>] lock_acquire+0x2a2/0x790 kernel/locking/lockdep.c:3749
[< inline >] __mutex_lock_common kernel/locking/mutex.c:521
[<ffffffff88195bcf>] mutex_lock_nested+0x23f/0xf20 kernel/locking/mutex.c:621
[< inline >] genl_lock net/netlink/genetlink.c:31
[<ffffffff86cc0c26>] genl_lock_dumpit+0x46/0xa0 net/netlink/genetlink.c:518
[<ffffffff86cb33ac>] netlink_dump+0x57c/0xd70 net/netlink/af_netlink.c:2127
[<ffffffff86cb7b6a>] __netlink_dump_start+0x4ea/0x760
net/netlink/af_netlink.c:2217
[<ffffffff86cc2319>] genl_family_rcv_msg+0xdc9/0x1070
net/netlink/genetlink.c:586
[<ffffffff86cc2770>] genl_rcv_msg+0x1b0/0x260 net/netlink/genetlink.c:660
[<ffffffff86cc034c>] netlink_rcv_skb+0x2bc/0x3a0 net/netlink/af_netlink.c:2298
[<ffffffff86cc153d>] genl_rcv+0x2d/0x40 net/netlink/genetlink.c:671
[< inline >] netlink_unicast_kernel net/netlink/af_netlink.c:1231
[<ffffffff86cbeb6a>] netlink_unicast+0x51a/0x740 net/netlink/af_netlink.c:1257
[<ffffffff86cbf834>] netlink_sendmsg+0xaa4/0xe50 net/netlink/af_netlink.c:1803
[< inline >] sock_sendmsg_nosec net/socket.c:621
[<ffffffff86a7618f>] sock_sendmsg+0xcf/0x110 net/socket.c:631
[<ffffffff86a764fb>] sock_write_iter+0x32b/0x620 net/socket.c:829
[< inline >] new_sync_write fs/read_write.c:499
[<ffffffff81a701ae>] __vfs_write+0x4fe/0x830 fs/read_write.c:512
[<ffffffff81a71c55>] vfs_write+0x175/0x4e0 fs/read_write.c:560
[< inline >] SYSC_write fs/read_write.c:607
[<ffffffff81a760e0>] SyS_write+0x100/0x240 fs/read_write.c:599
[<ffffffff881a5f85>] entry_SYSCALL_64_fastpath+0x23/0xc6

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