[syzbot] [net?] WARNING in __linkwatch_sync_dev

[syzbot]

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+48c14f...@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>


---
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[Stanislav Fomichev]

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

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 7702d0130dc0 Add linux-next specific files for 20250408
git tree: linux-next

console+strace: https://syzkaller.appspot.com/x/log.txt?x=138fa7e4580000

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

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11520398580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16b1323f980000

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+48c14f...@syzkaller.appspotmail.com

------------[ cut here ]------------
RTNL: assertion failed at ./include/net/netdev_lock.h (56)

WARNING: CPU: 1 PID: 12 at ./include/net/netdev_lock.h:56 netdev_ops_assert_locked include/net/netdev_lock.h:56 [inline]
WARNING: CPU: 1 PID: 12 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: 12 Comm: kworker/u8:0 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:ffffc90000117710 EFLAGS: 00010246
RAX: 6875daac7c816500 RBX: 0000000000000000 RCX: ffff88801c685a00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffff81824ed2 R09: fffffbfff1d7a700
R10: dffffc0000000000 R11: fffffbfff1d7a700 R12: 0000000000000000
R13: dffffc0000000000 R14: ffff888034096008 R15: ffff888034096000

FS: 0000000000000000(0000) GS:ffff888125089000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007fa9d1a29440 CR3: 0000000075fc0000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 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>


---

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[syzbot]

syzbot has bisected this issue to:

commit 00b35530811f2aa3d7ceec2dbada80861c7632a8
Author: Eric Dumazet <edum...@google.com>
Date: Thu Feb 6 14:04:22 2025 +0000

batman-adv: adopt netdev_hold() / netdev_put()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=175db74c580000
start commit: 7702d0130dc0 Add linux-next specific files for 20250408
git tree: linux-next
final oops: https://syzkaller.appspot.com/x/report.txt?x=14ddb74c580000
console output: https://syzkaller.appspot.com/x/log.txt?x=10ddb74c580000

kernel config: https://syzkaller.appspot.com/x/.config?x=91edf513888f57d7
dashboard link: https://syzkaller.appspot.com/bug?extid=48c14f61594bdfadb086

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11520398580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16b1323f980000

Reported-by: syzbot+48c14f...@syzkaller.appspotmail.com
Fixes: 00b35530811f ("batman-adv: adopt netdev_hold() / netdev_put()")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection