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

[syzbot <syzbot+1bd67523d909320dd9e2@syzkaller.appspotmail.com>]

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+1bd67523d909320dd9e2@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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