[v6.1] INFO: rcu detected stall in chrdev_open (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4931e0e1673d Linux 6.1.170
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=14efda36580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0605c5af04d7603
dashboard link: https://syzkaller.appspot.com/bug?extid=8134f525d5bd4936c0d9
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cd62baf6f839/disk-4931e0e1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/28b9d34fdc6c/vmlinux-4931e0e1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5056ec0ca104/bzImage-4931e0e1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8134f5...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 0-.... } 2653 jiffies s: 116673 root: 0x1/.
rcu: blocking rcu_node structures (internal RCU debug):
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 27867 Comm: syz.1.5512 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:asm_sysvec_irq_work+0x0/0x20 arch/x86/include/asm/idtentry.h:722
Code: e9 b5 03 00 00 90 90 90 90 90 0f 01 ca fc 6a ff e8 b5 02 00 00 48 89 c4 48 89 e7 e8 ea b0 ed ff e9 95 03 00 00 90 90 90 90 90 <0f> 01 ca fc 6a ff e8 95 02 00 00 48 89 c4 48 89 e7 e8 ba b5 ed ff
RSP: 0018:ffffc90000007a98 EFLAGS: 00000006
RAX: 9484ab7c60fcca00 RBX: 1ffff92000000f60 RCX: 9484ab7c60fcca00
RDX: dffffc0000000000 RSI: ffffffff8a8c1120 RDI: ffffffff8adf1320
RBP: ffffc90000007bb0 R08: ffffffff90af9277 R09: 1ffffffff215f24e
R10: dffffc0000000000 R11: fffffbfff215f24f R12: 0000000000000246
R13: dffffc0000000000 R14: ffff8880b8e3b900 R15: 0000000000000001
FS: 00007f143f6686c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fab03d456b8 CR3: 0000000031bd6000 CR4: 00000000003506f0
DR0: 0000200000000300 DR1: 0000200000000300 DR2: 0000200000000300
DR3: 0000200000000300 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
<IRQ>
RIP: 0010:rcu_read_unlock_special+0x7f/0x510 kernel/rcu/tree_plugin.h:685
Code: eb 03 48 b8 f1 f1 f1 f1 f8 f2 f2 f2 4a 89 04 2b 42 c7 44 2b 08 f8 f3 f3 f3 65 44 8b 35 d2 33 95 7e 41 f7 c6 00 00 f0 00 74 40 <48> c7 44 24 40 0e 36 e0 45 4a c7 04 2b 00 00 00 00 42 c7 44 2b 08
RSP: 0018:ffffc90000007ac0 EFLAGS: 00000206
__rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:426
rcu_read_unlock include/linux/rcupdate.h:823 [inline]
ieee80211_iterate_active_interfaces_atomic+0x156/0x170 net/mac80211/util.c:826
mac80211_hwsim_beacon+0xb7/0x1b0 drivers/net/wireless/mac80211_hwsim.c:2147
__run_hrtimer kernel/time/hrtimer.c:1747 [inline]
__hrtimer_run_queues+0x54a/0xd50 kernel/time/hrtimer.c:1811
hrtimer_run_softirq+0x183/0x2a0 kernel/time/hrtimer.c:1828
handle_softirqs+0x2a1/0x930 kernel/softirq.c:596
__do_softirq kernel/softirq.c:630 [inline]
invoke_softirq kernel/softirq.c:470 [inline]
__irq_exit_rcu+0x13b/0x230 kernel/softirq.c:679
irq_exit_rcu+0x5/0x20 kernel/softirq.c:691
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1118
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:arch_stack_walk+0x115/0x140 arch/x86/kernel/stacktrace.c:30
Code: 89 ff e8 ce 8e 08 00 48 85 c0 74 1e 48 89 df 48 89 c6 41 ff d6 84 c0 74 11 4c 89 ff e8 d4 8f 08 00 83 bd 78 ff ff ff 00 75 d5 <65> 48 8b 04 25 28 00 00 00 48 3b 45 d8 75 0d 48 83 c4 68 5b 41 5c
RSP: 0018:ffffc900049ff4a8 EFLAGS: 00000246
RAX: 0000000000000000 RBX: ffffc900049ff560 RCX: 9484ab7c60fcca00
RDX: 0000000000000000 RSI: ffffffff8a8c22a0 RDI: ffffffff8adf1320
RBP: ffffc900049ff530 R08: ffffffff8e1ff3ef R09: 1ffffffff1c3fe7d
R10: dffffc0000000000 R11: fffffbfff1c3fe7e R12: ffff88802fff5940
R13: dffffc0000000000 R14: ffffffff817122e0 R15: ffffc900049ff4a8
stack_trace_save+0xa6/0xf0 kernel/stacktrace.c:122
ref_tracker_alloc+0x1a3/0x4b0 lib/ref_tracker.c:91
netns_tracker_alloc include/net/net_namespace.h:328 [inline]
get_net_track include/net/net_namespace.h:344 [inline]
sk_alloc+0x1ad/0x340 net/core/sock.c:2120
tun_chr_open+0x75/0x4d0 drivers/net/tun.c:3456
misc_open+0x31f/0x390 drivers/char/misc.c:145
chrdev_open+0x5c5/0x6a0 fs/char_dev.c:414
do_dentry_open+0x7e9/0x10d0 fs/open.c:882
do_open fs/namei.c:3634 [inline]
path_openat+0x2635/0x2ee0 fs/namei.c:3791
do_filp_open+0x1f1/0x430 fs/namei.c:3818
do_sys_openat2+0x150/0x4b0 fs/open.c:1320
do_sys_open fs/open.c:1336 [inline]
__do_sys_openat fs/open.c:1352 [inline]
__se_sys_openat fs/open.c:1347 [inline]
__x64_sys_openat+0x135/0x160 fs/open.c:1347
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f143e79cdd9
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:00007f143f668028 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f143ea15fa0 RCX: 00007f143e79cdd9
RDX: 0000000000000800 RSI: 00002000000000c0 RDI: ffffffffffffff9c
RBP: 00007f143e832d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f143ea16038 R14: 00007f143ea15fa0 R15: 00007ffd60e6b4c8
</TASK>


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