[syzbot] [net?] possible deadlock in dev_close

[syzbot] [net?] possible deadlock in dev_close

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    0c86b42439b6 Merge tag 'drm-next-2025-03-28' of https://gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1353c678580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=500ed53123ea6589
dashboard link: https://syzkaller.appspot.com/bug?extid=9f46f55b69eb4f3e054b
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-0c86b424.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3e78f55971a9/vmlinux-0c86b424.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3f8acc0407dd/bzImage-0c86b424.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9f46f55b69eb4f3e054b@syzkaller.appspotmail.com

loop0: detected capacity change from 0 to 1024
netlink: 36 bytes leftover after parsing attributes in process `syz.0.0'.
netlink: 'syz.0.0': attribute type 10 has an invalid length.
bond0: (slave netdevsim0): Enslaving as an active interface with an up link
bond0: (slave netdevsim0): Releasing backup interface
============================================
WARNING: possible recursive locking detected
6.14.0-syzkaller-09352-g0c86b42439b6 #0 Not tainted
--------------------------------------------
syz.0.0/5321 is trying to acquire lock:
ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: dev_close+0x121/0x280 net/core/dev_api.c:224

but task is already holding lock:
ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: do_setlink+0x209/0x4370 net/core/rtnetlink.c:3025

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&dev->lock);
  lock(&dev->lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz.0.0/5321:
 #0: ffffffff900e5f48 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline]
 #0: ffffffff900e5f48 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock net/core/rtnetlink.c:341 [inline]
 #0: ffffffff900e5f48 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0xd68/0x1fe0 net/core/rtnetlink.c:4061
 #1: ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
 #1: ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
 #1: ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: do_setlink+0x209/0x4370 net/core/rtnetlink.c:3025

stack backtrace:
CPU: 0 UID: 0 PID: 5321 Comm: syz.0.0 Not tainted 6.14.0-syzkaller-09352-g0c86b42439b6 #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_deadlock_bug+0x2be/0x2d0 kernel/locking/lockdep.c:3042
 check_deadlock kernel/locking/lockdep.c:3094 [inline]
 validate_chain+0x928/0x24e0 kernel/locking/lockdep.c:3896
 __lock_acquire+0xad5/0xd80 kernel/locking/lockdep.c:5235
 lock_acquire+0x116/0x2f0 kernel/locking/lockdep.c:5866
 __mutex_lock_common kernel/locking/mutex.c:587 [inline]
 __mutex_lock+0x1a5/0x10c0 kernel/locking/mutex.c:732
 netdev_lock include/linux/netdevice.h:2751 [inline]
 netdev_lock_ops include/net/netdev_lock.h:42 [inline]
 dev_close+0x121/0x280 net/core/dev_api.c:224
 __bond_release_one+0xcaf/0x1220 drivers/net/bonding/bond_main.c:2629
 bond_slave_netdev_event drivers/net/bonding/bond_main.c:4028 [inline]
 bond_netdev_event+0x557/0xfb0 drivers/net/bonding/bond_main.c:4146
 notifier_call_chain+0x1a5/0x3f0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2218 [inline]
 call_netdevice_notifiers net/core/dev.c:2232 [inline]
 netif_change_net_namespace+0xa30/0x1c20 net/core/dev.c:12163
 do_setlink+0x3aa/0x4370 net/core/rtnetlink.c:3042
 rtnl_changelink net/core/rtnetlink.c:3766 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3925 [inline]
 rtnl_newlink+0x17e2/0x1fe0 net/core/rtnetlink.c:4062
 rtnetlink_rcv_msg+0x80f/0xd70 net/core/rtnetlink.c:6952
 netlink_rcv_skb+0x208/0x480 net/netlink/af_netlink.c:2534
 netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
 netlink_unicast+0x7f8/0x9a0 net/netlink/af_netlink.c:1339
 netlink_sendmsg+0x8e8/0xce0 net/netlink/af_netlink.c:1883
 sock_sendmsg_nosec net/socket.c:712 [inline]
 __sock_sendmsg+0x221/0x270 net/socket.c:727
 ____sys_sendmsg+0x53c/0x870 net/socket.c:2566
 ___sys_sendmsg net/socket.c:2620 [inline]
 __sys_sendmsg+0x271/0x360 net/socket.c:2652
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb17b38d169
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fb17c2be038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fb17b5a5fa0 RCX: 00007fb17b38d169
RDX: 0000000000000000 RSI: 0000200000000340 RDI: 0000000000000008
RBP: 00007fb17b40e2a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fb17b5a5fa0 R15: 00007fff2d1aa5d8
 </TASK>


---
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Re: [syzbot] [net?] possible deadlock in dev_close

[Stanislav Fomichev]

On 04/01, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    0c86b42439b6 Merge tag 'drm-next-2025-03-28' of https://gi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1353c678580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=500ed53123ea6589
> dashboard link: https://syzkaller.appspot.com/bug?extid=9f46f55b69eb4f3e054b
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-0c86b424.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/3e78f55971a9/vmlinux-0c86b424.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/3f8acc0407dd/bzImage-0c86b424.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+9f46f55b69eb4f3e054b@syzkaller.appspotmail.com
> 
> loop0: detected capacity change from 0 to 1024
> netlink: 36 bytes leftover after parsing attributes in process `syz.0.0'.
> netlink: 'syz.0.0': attribute type 10 has an invalid length.
> bond0: (slave netdevsim0): Enslaving as an active interface with an up link
> bond0: (slave netdevsim0): Releasing backup interface
> ============================================
> WARNING: possible recursive locking detected
> 6.14.0-syzkaller-09352-g0c86b42439b6 #0 Not tainted
> --------------------------------------------
> syz.0.0/5321 is trying to acquire lock:
> ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
> ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
> ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: dev_close+0x121/0x280 net/core/dev_api.c:224
> 
> but task is already holding lock:
> ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
> ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
> ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: do_setlink+0x209/0x4370 net/core/rtnetlink.c:3025
> 
> other info that might help us debug this:
>  Possible unsafe locking scenario:
> 
>        CPU0
>        ----
>   lock(&dev->lock);
>   lock(&dev->lock);
> 
>  *** DEADLOCK ***
> 
>  May be due to missing lock nesting notation
> 
> 2 locks held by syz.0.0/5321:
>  #0: ffffffff900e5f48 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline]
>  #0: ffffffff900e5f48 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock net/core/rtnetlink.c:341 [inline]
>  #0: ffffffff900e5f48 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0xd68/0x1fe0 net/core/rtnetlink.c:4061
>  #1: ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
>  #1: ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
>  #1: ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: do_setlink+0x209/0x4370 net/core/rtnetlink.c:3025
> 
> stack backtrace:
> CPU: 0 UID: 0 PID: 5321 Comm: syz.0.0 Not tainted 6.14.0-syzkaller-09352-g0c86b42439b6 #0 PREEMPT(full) 
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:94 [inline]
>  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
>  print_deadlock_bug+0x2be/0x2d0 kernel/locking/lockdep.c:3042
>  check_deadlock kernel/locking/lockdep.c:3094 [inline]
>  validate_chain+0x928/0x24e0 kernel/locking/lockdep.c:3896
>  __lock_acquire+0xad5/0xd80 kernel/locking/lockdep.c:5235
>  lock_acquire+0x116/0x2f0 kernel/locking/lockdep.c:5866
>  __mutex_lock_common kernel/locking/mutex.c:587 [inline]
>  __mutex_lock+0x1a5/0x10c0 kernel/locking/mutex.c:732
>  netdev_lock include/linux/netdevice.h:2751 [inline]
>  netdev_lock_ops include/net/netdev_lock.h:42 [inline]
>  dev_close+0x121/0x280 net/core/dev_api.c:224
>  __bond_release_one+0xcaf/0x1220 drivers/net/bonding/bond_main.c:2629
>  bond_slave_netdev_event drivers/net/bonding/bond_main.c:4028 [inline]
>  bond_netdev_event+0x557/0xfb0 drivers/net/bonding/bond_main.c:4146
>  notifier_call_chain+0x1a5/0x3f0 kernel/notifier.c:85
>  call_netdevice_notifiers_extack net/core/dev.c:2218 [inline]
>  call_netdevice_notifiers net/core/dev.c:2232 [inline]
>  netif_change_net_namespace+0xa30/0x1c20 net/core/dev.c:12163
>  do_setlink+0x3aa/0x4370 net/core/rtnetlink.c:3042

Looks like it is UNREGISTER notifier for bond. I think this is gonna be
(accidentally) fixed by https://lore.kernel.org/netdev/20250401163452.622454-3-sdf@fomichev.me/T/#u
which stops grabbing instance lock during UNREGISTER.

Re: [syzbot] [net?] possible deadlock in dev_close

[Taehee Yoo]

On Wed, Apr 2, 2025 at 11:27 PM Stanislav Fomichev <stfomichev@gmail.com> wrote:
>

Hi Stanislav,

> On 04/01, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    0c86b42439b6 Merge tag 'drm-next-2025-03-28' of https://gi..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1353c678580000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=500ed53123ea6589
> > dashboard link: https://syzkaller.appspot.com/bug?extid=9f46f55b69eb4f3e054b
> > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > Downloadable assets:
> > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-0c86b424.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/3e78f55971a9/vmlinux-0c86b424.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/3f8acc0407dd/bzImage-0c86b424.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+9f46f55b69eb4f3e054b@syzkaller.appspotmail.com
> >
> > loop0: detected capacity change from 0 to 1024
> > netlink: 36 bytes leftover after parsing attributes in process `syz.0.0'.
> > netlink: 'syz.0.0': attribute type 10 has an invalid length.
> > bond0: (slave netdevsim0): Enslaving as an active interface with an up link
> > bond0: (slave netdevsim0): Releasing backup interface
> > ============================================
> > WARNING: possible recursive locking detected
> > 6.14.0-syzkaller-09352-g0c86b42439b6 #0 Not tainted
> > --------------------------------------------
> > syz.0.0/5321 is trying to acquire lock:
> > ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
> > ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
> > ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: dev_close+0x121/0x280 net/core/dev_api.c:224
> >
> > but task is already holding lock:
> > ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
> > ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
> > ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: do_setlink+0x209/0x4370 net/core/rtnetlink.c:3025
> >
> > other info that might help us debug this:
> >  Possible unsafe locking scenario:
> >
> >        CPU0
> >        ----
> >   lock(&dev->lock);
> >   lock(&dev->lock);
> >
> >  *** DEADLOCK ***
> >
> >  May be due to missing lock nesting notation
> >
> > 2 locks held by syz.0.0/5321:
> >  #0: ffffffff900e5f48 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline]
> >  #0: ffffffff900e5f48 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock net/core/rtnetlink.c:341 [inline]
> >  #0: ffffffff900e5f48 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0xd68/0x1fe0 net/core/rtnetlink.c:4061
> >  #1: ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
> >  #1: ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
> >  #1: ffff888042eccd28 (&dev->lock){+.+.}-{4:4}, at: do_setlink+0x209/0x4370 net/core/rtnetlink.c:3025
> >
> > stack backtrace:
> > CPU: 0 UID: 0 PID: 5321 Comm: syz.0.0 Not tainted 6.14.0-syzkaller-09352-g0c86b42439b6 #0 PREEMPT(full)
> > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> > Call Trace:
> >  <TASK>
> >  __dump_stack lib/dump_stack.c:94 [inline]
> >  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
> >  print_deadlock_bug+0x2be/0x2d0 kernel/locking/lockdep.c:3042
> >  check_deadlock kernel/locking/lockdep.c:3094 [inline]
> >  validate_chain+0x928/0x24e0 kernel/locking/lockdep.c:3896
> >  __lock_acquire+0xad5/0xd80 kernel/locking/lockdep.c:5235
> >  lock_acquire+0x116/0x2f0 kernel/locking/lockdep.c:5866
> >  __mutex_lock_common kernel/locking/mutex.c:587 [inline]
> >  __mutex_lock+0x1a5/0x10c0 kernel/locking/mutex.c:732
> >  netdev_lock include/linux/netdevice.h:2751 [inline]
> >  netdev_lock_ops include/net/netdev_lock.h:42 [inline]
> >  dev_close+0x121/0x280 net/core/dev_api.c:224
> >  __bond_release_one+0xcaf/0x1220 drivers/net/bonding/bond_main.c:2629
> >  bond_slave_netdev_event drivers/net/bonding/bond_main.c:4028 [inline]
> >  bond_netdev_event+0x557/0xfb0 drivers/net/bonding/bond_main.c:4146
> >  notifier_call_chain+0x1a5/0x3f0 kernel/notifier.c:85
> >  call_netdevice_notifiers_extack net/core/dev.c:2218 [inline]
> >  call_netdevice_notifiers net/core/dev.c:2232 [inline]
> >  netif_change_net_namespace+0xa30/0x1c20 net/core/dev.c:12163
> >  do_setlink+0x3aa/0x4370 net/core/rtnetlink.c:3042
>
> Looks like it is UNREGISTER notifier for bond. I think this is gonna be
> (accidentally) fixed by https://lore.kernel.org/netdev/20250401163452.622454-3-sdf@fomichev.me/T/#u
> which stops grabbing instance lock during UNREGISTER.
>

I found a reproducer.
    interface=<physical interface>
    ip netns add ns_test
    ip link add bond0 type bond
    ip link set $interface master bond0 netns ns_test

So, deadlock occurs, and the splat is the same as in this report.

As you mentioned, I applied[1] and tested again.
I can't see any deadlock or warning.

[1] https://lore.kernel.org/netdev/20250401163452.622454-3-sdf@fomichev.me/T/#u

Thanks a lot!
Taehee Yoo