Re: [syzbot] [net?] WARNING in __linkwatch_sync_dev

[Stanislav Fomichev <stfomichev@gmail.com>]

On 04/08, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    7702d0130dc0 Add linux-next specific files for 20250408
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=15fe8070580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=91edf513888f57d7
> dashboard link: https://syzkaller.appspot.com/bug?extid=48c14f61594bdfadb086
> 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: https://storage.googleapis.com/syzbot-assets/0603dd3556b9/disk-7702d013.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/d384baaee881/vmlinux-7702d013.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/1ac172735b6c/bzImage-7702d013.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+48c14f61594bdfadb086@syzkaller.appspotmail.com
> 
> ------------[ cut here ]------------
> RTNL: assertion failed at ./include/net/netdev_lock.h (56)
> WARNING: CPU: 1 PID: 2971 at ./include/net/netdev_lock.h:56 netdev_ops_assert_locked include/net/netdev_lock.h:56 [inline]
> WARNING: CPU: 1 PID: 2971 at ./include/net/netdev_lock.h:56 __linkwatch_sync_dev+0x30d/0x360 net/core/link_watch.c:279
> Modules linked in:
> CPU: 1 UID: 0 PID: 2971 Comm: kworker/u8:8 Not tainted 6.15.0-rc1-next-20250408-syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
> Workqueue: bond0 bond_mii_monitor
> RIP: 0010:netdev_ops_assert_locked include/net/netdev_lock.h:56 [inline]
> RIP: 0010:__linkwatch_sync_dev+0x30d/0x360 net/core/link_watch.c:279
> Code: 7c fe ff ff e8 f4 63 cc f7 c6 05 83 28 53 06 01 90 48 c7 c7 60 5c 51 8d 48 c7 c6 8a 9b 67 8e ba 38 00 00 00 e8 04 6b 8b f7 90 <0f> 0b 90 90 e9 4d fe ff ff 89 d9 80 e1 07 38 c1 0f 8c 19 fd ff ff
> RSP: 0018:ffffc9000b767710 EFLAGS: 00010246
> RAX: bb6ea754fa006300 RBX: 0000000000000000 RCX: ffff888030979e00
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
> RBP: 0000000000000000 R08: ffffffff81824ed2 R09: 1ffffffff20c01c6
> R10: dffffc0000000000 R11: fffffbfff20c01c7 R12: 0000000000000000
> R13: dffffc0000000000 R14: ffff88805d768008 R15: ffff88805d768000
> FS:  0000000000000000(0000) GS:ffff888125089000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f85e8c4df98 CR3: 000000006a050000 CR4: 00000000003526f0
> DR0: 0000000000000099 DR1: 0000000000000000 DR2: 000000000000000b
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  ethtool_op_get_link+0x15/0x60 net/ethtool/ioctl.c:63
>  bond_check_dev_link+0x1fb/0x4b0 drivers/net/bonding/bond_main.c:864
>  bond_miimon_inspect drivers/net/bonding/bond_main.c:2734 [inline]
>  bond_mii_monitor+0x49d/0x3170 drivers/net/bonding/bond_main.c:2956
>  process_one_work kernel/workqueue.c:3238 [inline]
>  process_scheduled_works+0xac3/0x18e0 kernel/workqueue.c:3319
>  worker_thread+0x870/0xd50 kernel/workqueue.c:3400
>  kthread+0x7b7/0x940 kernel/kthread.c:464
>  ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>  </TASK>

This needs ops lock/unlock around get_link in bond_check_dev_link, will
follow up.