[syzbot] [kernfs?] INFO: rcu detected stall in cleanup_net (8)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 008d3547aae5 Add linux-next specific files for 20251210
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=147c3a1a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=a94030c847137a18
dashboard link: https://syzkaller.appspot.com/bug?extid=0604401cc084920f6c3d
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13f9deb4580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1406b992580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f5497242418d/disk-008d3547.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/46fd6edd4284/vmlinux-008d3547.xz
kernel image: https://storage.googleapis.com/syzbot-assets/61e6e2e573e8/bzImage-008d3547.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+060440...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P5930/1:b..l
rcu: (detected by 1, t=10502 jiffies, g=11645, q=51 ncpus=2)
task:kworker/u8:12 state:R running task stack:22432 pid:5930 tgid:5930 ppid:2 task_flags:0x4208060 flags:0x00080000
Workqueue: netns cleanup_net
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5256 [inline]
__schedule+0x14bc/0x5000 kernel/sched/core.c:6863
preempt_schedule_irq+0xb5/0x150 kernel/sched/core.c:7190
irqentry_exit+0x5d8/0x660 kernel/entry/common.c:216
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:rcu_is_watching+0x67/0xb0 kernel/rcu/tree.c:752
Code: 89 f7 e8 0c 71 80 00 48 c7 c3 d8 f6 7f 92 49 03 1e 48 89 d8 48 c1 e8 03 42 0f b6 04 38 84 c0 75 34 8b 03 65 ff 0d 79 1d d7 10 <74> 11 83 e0 04 c1 e8 02 5b 41 5e 41 5f e9 97 d8 b6 09 cc e8 71 d5
RSP: 0018:ffffc900043af018 EFLAGS: 00000286
RAX: 000000000003f46c RBX: ffff8880b86336d8 RCX: 1e5222b0fc0eb100
RDX: 000000005b9ddbdf RSI: ffffffff8bc07c40 RDI: ffffffff8bc07c00
RBP: dffffc0000000000 R08: ffffffff81743f85 R09: ffffffff8df41a60
R10: ffffc900043af158 R11: ffffffff81ada810 R12: 1ffff92000875e21
R13: ffffc900043af140 R14: ffffffff8d9b1dd0 R15: dffffc0000000000
rcu_read_lock include/linux/rcupdate.h:868 [inline]
class_rcu_constructor include/linux/rcupdate.h:1195 [inline]
unwind_next_frame+0xd4/0x2390 arch/x86/kernel/unwind_orc.c:479
arch_stack_walk+0x11c/0x150 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
poison_slab_object mm/kasan/common.c:253 [inline]
__kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:2540 [inline]
slab_free mm/slub.c:6668 [inline]
kfree+0x1c0/0x660 mm/slub.c:6876
devinet_sysctl_unregister net/ipv4/devinet.c:2729 [inline]
inetdev_destroy net/ipv4/devinet.c:334 [inline]
inetdev_event+0x78e/0x15b0 net/ipv4/devinet.c:1655
notifier_call_chain+0x19d/0x3a0 kernel/notifier.c:85
call_netdevice_notifiers_extack net/core/dev.c:2269 [inline]
call_netdevice_notifiers net/core/dev.c:2283 [inline]
unregister_netdevice_many_notify+0x1867/0x2340 net/core/dev.c:12400
unregister_netdevice_many net/core/dev.c:12463 [inline]
default_device_exit_batch+0x964/0x9e0 net/core/dev.c:13055
ops_exit_list net/core/net_namespace.c:205 [inline]
ops_undo_list+0x525/0x990 net/core/net_namespace.c:252
cleanup_net+0x4d8/0x7a0 net/core/net_namespace.c:696
process_one_work+0x93a/0x15a0 kernel/workqueue.c:3279
process_scheduled_works kernel/workqueue.c:3362 [inline]
worker_thread+0x9b0/0xee0 kernel/workqueue.c:3443
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
</TASK>
rcu: rcu_preempt kthread starved for 10553 jiffies! g11645 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt state:R running task stack:27736 pid:16 tgid:16 ppid:2 task_flags:0x208040 flags:0x00080000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5256 [inline]
__schedule+0x14bc/0x5000 kernel/sched/core.c:6863
__schedule_loop kernel/sched/core.c:6945 [inline]
schedule+0x165/0x360 kernel/sched/core.c:6960
schedule_timeout+0x12b/0x270 kernel/time/sleep_timeout.c:99
rcu_gp_fqs_loop+0x301/0x1540 kernel/rcu/tree.c:2083
rcu_gp_kthread+0x99/0x390 kernel/rcu/tree.c:2285
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
</TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:pv_native_safe_halt+0x13/0x20 arch/x86/kernel/paravirt.c:82
Code: 13 ee 02 00 cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 73 c0 0c 00 f3 0f 1e fa fb f4 <c3> cc cc cc cc cc cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90
RSP: 0018:ffffc90000197de0 EFLAGS: 000002c6
RAX: 2bdaeed9ae4cb000 RBX: ffffffff8197971a RCX: 2bdaeed9ae4cb000
RDX: 0000000000000001 RSI: ffffffff8d791c9e RDI: ffffffff8bc07c60
RBP: ffffc90000197f10 R08: ffff8880b87336db R09: 1ffff110170e66db
R10: dffffc0000000000 R11: ffffed10170e66dc R12: ffffffff8f820770
R13: 1ffff110039dcb70 R14: 0000000000000001 R15: 0000000000000001
FS: 0000000000000000(0000) GS:ffff888125f34000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffee7189228 CR3: 00000000753b0000 CR4: 00000000003526f0
Call Trace:
<TASK>
arch_safe_halt arch/x86/include/asm/paravirt.h:107 [inline]
default_idle+0x13/0x20 arch/x86/kernel/process.c:767
default_idle_call+0x73/0xb0 kernel/sched/idle.c:122
cpuidle_idle_call kernel/sched/idle.c:191 [inline]
do_idle+0x1ea/0x520 kernel/sched/idle.c:332
cpu_startup_entry+0x44/0x60 kernel/sched/idle.c:430
start_secondary+0x101/0x110 arch/x86/kernel/smpboot.c:312
common_startup_64+0x13e/0x147
</TASK>


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