[v6.6] INFO: rcu detected stall in __tun_chr_ioctl (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d1cfde2d5d15 Linux 6.6.143
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=164ab9fa580000
kernel config: https://syzkaller.appspot.com/x/.config?x=441765643cbfb8d
dashboard link: https://syzkaller.appspot.com/bug?extid=8b4ff2a7f5a77cb64934
compiler: Debian clang version 22.1.6 (++20260514074242+fc4aad7b5db3-1~exp1~20260514074407.73), Debian LLD 22.1.6

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/65f04d62b48f/disk-d1cfde2d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6a803b737439/vmlinux-d1cfde2d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e621f8d5e524/bzImage-d1cfde2d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8b4ff2...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 0-....: (1 GPs behind) idle=c3d4/1/0x4000000000000000 softirq=24447/24449 fqs=5247
rcu: hardirqs softirqs csw/system
rcu: number: 1341643 0 0
rcu: cputime: 16103 36376 63 ==> 52490(ms)
rcu: (t=10501 jiffies g=29753 q=2398 ncpus=2)
CPU: 0 PID: 7811 Comm: syz.3.600 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:lock_acquire+0x208/0x420 kernel/locking/lockdep.c:5758
Code: f7 84 24 80 00 00 00 00 02 00 00 43 c6 44 3c 04 f8 0f 85 f0 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 04 3c 00 00 00 00 43 c7 44 3c 08 00 00 00 00 65 48 8b 04 25
RSP: 0018:ffffc900000078e0 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 473184ae8b70bd00
RDX: 0000000000000000 RSI: ffffffff8acadce0 RDI: ffffffff8b1c7be0
RBP: ffffc900000079e8 R08: dffffc0000000000 R09: 1ffffffff22378a0
R10: dffffc0000000000 R11: fffffbfff22378a1 R12: 1ffff92000000f28
R13: ffffffff8d131da0 R14: 0000000000000246 R15: dffffc0000000000
FS: 00007f7bd03306c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7d25def4b8 CR3: 0000000026235000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 00000000000f0602
Call Trace:
<IRQ>
rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
rcu_read_lock include/linux/rcupdate.h:786 [inline]
__rhashtable_remove_fast include/linux/rhashtable.h:1084 [inline]
rhashtable_remove_fast include/linux/rhashtable.h:1122 [inline]
inet_frag_kill+0x303/0x10d0 net/ipv4/inet_fragment.c:280
ipq_kill net/ipv4/ip_fragment.c:123 [inline]
ip_expire+0x19f/0x770 net/ipv4/ip_fragment.c:157
call_timer_fn+0x189/0x540 kernel/time/timer.c:1701
expire_timers kernel/time/timer.c:1752 [inline]
__run_timers+0x570/0x810 kernel/time/timer.c:2023
run_timer_softirq+0x67/0xf0 kernel/time/timer.c:2036
handle_softirqs+0x27d/0x820 kernel/softirq.c:578
__do_softirq kernel/softirq.c:612 [inline]
invoke_softirq kernel/softirq.c:452 [inline]
__irq_exit_rcu+0xd3/0x190 kernel/softirq.c:661
irq_exit_rcu+0x9/0x20 kernel/softirq.c:673
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1088
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:finish_task_switch+0x267/0x8f0 kernel/sched/core.c:5255
Code: 26 09 85 c0 0f 84 30 01 00 00 48 85 db 0f 85 4f 01 00 00 0f 1f 44 00 00 4c 89 e7 e8 93 3b 30 09 e8 7e 0b 30 00 fb 4c 8b 65 b8 <49> 8d bc 24 f8 15 00 00 48 89 f8 48 c1 e8 03 42 0f b6 04 30 84 c0
RSP: 0018:ffffc9000fdbf580 EFLAGS: 00000282
RAX: 473184ae8b70bd00 RBX: 0000000000000000 RCX: 473184ae8b70bd00
RDX: dffffc0000000000 RSI: ffffffff8acacb60 RDI: ffffffff8b1c7be0
RBP: ffffc9000fdbf5d0 R08: ffffffff911bc507 R09: 1ffffffff22378a0
R10: dffffc0000000000 R11: fffffbfff22378a1 R12: ffff88802b94da00
R13: 1ffff110171c79a9 R14: dffffc0000000000 R15: ffff8880b8e3cd48
context_switch kernel/sched/core.c:5384 [inline]
__schedule+0x15b6/0x4660 kernel/sched/core.c:6700
schedule+0xbd/0x170 kernel/sched/core.c:6774
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:6833
__mutex_lock_common kernel/locking/mutex.c:679 [inline]
__mutex_lock+0x673/0xc80 kernel/locking/mutex.c:747
pcpu_alloc+0x287/0x1880 mm/percpu.c:1771
dev_map_notification+0x18f/0x9b0 kernel/bpf/devmap.c:1112
notifier_call_chain+0x18f/0x380 kernel/notifier.c:93
call_netdevice_notifiers_extack net/core/dev.c:2077 [inline]
call_netdevice_notifiers net/core/dev.c:2091 [inline]
register_netdevice+0x1670/0x1ba0 net/core/dev.c:10351
tun_set_iff+0x82b/0xea0 drivers/net/tun.c:2865
__tun_chr_ioctl+0x7e0/0x2070 drivers/net/tun.c:3134
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:871 [inline]
__se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f7bcf39de59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f7bd0330028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f7bcf625fa0 RCX: 00007f7bcf39de59
RDX: 0000200000000200 RSI: 00000000400454ca RDI: 000000000000000e
RBP: 00007f7bcf433e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7bcf626038 R14: 00007f7bcf625fa0 R15: 00007ffc2ef5dda8
</TASK>


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