[syzbot] [net?] WARNING: refcount bug in dev_deactivate_many

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f242ac4a0944 Merge tag 'x86-urgent-2026-03-29' of git://gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=165f90f2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=5a3e5e8c17cc174e
dashboard link: https://syzkaller.appspot.com/bug?extid=1bd67523d909320dd9e2
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a3583806d09a/disk-f242ac4a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0718400bb1a9/vmlinux-f242ac4a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b22f3be2e373/bzImage-f242ac4a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1bd675...@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: decrement hit 0; leaking memory.
WARNING: lib/refcount.c:31 at refcount_warn_saturate+0x7c/0x130 lib/refcount.c:31, CPU#0: kworker/u8:5/93
Modules linked in:
CPU: 0 UID: 0 PID: 93 Comm: kworker/u8:5 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: events_unbound linkwatch_event
RIP: 0010:refcount_warn_saturate+0x7c/0x130 lib/refcount.c:31
Code: c0 51 1a 8c e8 25 17 12 fd 83 fd 02 0f 84 a1 00 00 00 76 27 83 fd 03 74 7d 83 fd 04 75 3e e8 fb 1b 12 fd 48 8d 3d b4 57 ed 0b <67> 48 0f b9 3a e8 ea 1b 12 fd 5b 5d c3 cc cc cc cc 85 ed 74 3a e8
RSP: 0018:ffffc9000215f878 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff88802a98c664 RCX: ffffffff84f6dbcb
RDX: ffff88801e7924c0 RSI: ffffffff84f6dbe5 RDI: ffffffff90e433a0
RBP: 0000000000000004 R08: 0000000000000005 R09: 0000000000000004
R10: 0000000000000004 R11: 0000000000000000 R12: 1ffff9200042bf14
R13: ffff88802a98c664 R14: 0000000000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff88812433c000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2ff15ff8 CR3: 000000003954a000 CR4: 00000000003526f0
Call Trace:
<TASK>
__refcount_dec include/linux/refcount.h:461 [inline]
refcount_dec include/linux/refcount.h:476 [inline]
ref_tracker_free+0x5cd/0x6c0 lib/ref_tracker.c:303
netdev_tracker_free include/linux/netdevice.h:4456 [inline]
netdev_put include/linux/netdevice.h:4473 [inline]
netdev_put include/linux/netdevice.h:4469 [inline]
netdev_watchdog_down net/sched/sch_generic.c:575 [inline]
dev_deactivate_many+0x28f/0xfc0 net/sched/sch_generic.c:1337
dev_deactivate+0xf8/0x1c0 net/sched/sch_generic.c:1368
linkwatch_do_dev net/core/link_watch.c:184 [inline]
linkwatch_do_dev+0xce/0x110 net/core/link_watch.c:166
__linkwatch_run_queue+0x3a9/0x900 net/core/link_watch.c:240
linkwatch_event+0x8f/0xc0 net/core/link_watch.c:314
process_one_work+0xa23/0x19a0 kernel/workqueue.c:3276
process_scheduled_works kernel/workqueue.c:3359 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3440
kthread+0x370/0x450 kernel/kthread.c:436
ret_from_fork+0x754/0xd80 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
----------------
Code disassembly (best guess):
0: c0 51 1a 8c rclb $0x8c,0x1a(%rcx)
4: e8 25 17 12 fd call 0xfd12172e
9: 83 fd 02 cmp $0x2,%ebp
c: 0f 84 a1 00 00 00 je 0xb3
12: 76 27 jbe 0x3b
14: 83 fd 03 cmp $0x3,%ebp
17: 74 7d je 0x96
19: 83 fd 04 cmp $0x4,%ebp
1c: 75 3e jne 0x5c
1e: e8 fb 1b 12 fd call 0xfd121c1e
23: 48 8d 3d b4 57 ed 0b lea 0xbed57b4(%rip),%rdi # 0xbed57de
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2f: e8 ea 1b 12 fd call 0xfd121c1e
34: 5b pop %rbx
35: 5d pop %rbp
36: c3 ret
37: cc int3
38: cc int3
39: cc int3
3a: cc int3
3b: 85 ed test %ebp,%ebp
3d: 74 3a je 0x79
3f: e8 .byte 0xe8


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