[v5.15] INFO: rcu detected stall in tun_chr_write_iter

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: dc027a595035 Linux 5.15.209
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=165d6aae580000
kernel config: https://syzkaller.appspot.com/x/.config?x=353ae28c40b35af5
dashboard link: https://syzkaller.appspot.com/bug?extid=fa0ea0db5038c986b147
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/3d51783ddbbf/disk-dc027a59.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b6879bfcdc05/vmlinux-dc027a59.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e4755824edc0/bzImage-dc027a59.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fa0ea0...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 0-....: (1 GPs behind) idle=5d7/1/0x4000000000000000 softirq=62692/62693 fqs=5243
(detected by 1, t=10502 jiffies, g=92121, q=3830)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 20468 Comm: syz.1.3747 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:arch_irqs_disabled_flags arch/x86/include/asm/irqflags.h:127 [inline]
RIP: 0010:rcu_read_unlock_special+0xe2/0x4a0 kernel/rcu/tree_plugin.h:635
Code: 5d 41 5e 41 5f 5d c3 49 89 ff 42 c6 44 2b 08 00 48 c7 44 24 60 00 00 00 00 9c 8f 44 24 60 4c 8b 64 24 60 42 c6 44 2b 08 f8 fa <41> f7 c4 00 02 00 00 74 0f e8 f0 d5 19 00 66 45 85 f6 0f 84 d8 02
RSP: 0018:ffffc90000007060 EFLAGS: 00000046
RAX: f2f2f2f8f1f1f1f1 RBX: 1ffff92000000e10 RCX: ffff8880226d5940
RDX: 0000000000000100 RSI: ffffffff8a7a09a0 RDI: ffff8880226d5940
RBP: ffffc90000007140 R08: ffffffff8d8a06ef R09: 1ffffffff1b140dd
R10: dffffc0000000000 R11: fffffbfff1b140de R12: 0000000000000046
R13: dffffc0000000000 R14: 0000000000000101 R15: ffff8880226d5940
FS: 00007f68de1be6c0(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffe9e8acff8 CR3: 0000000047769000 CR4: 00000000003506f0
DR0: 0000000000000004 DR1: 0000200000000300 DR2: 0000200000000300
DR3: 0000200000000300 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
__rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:422
rcu_read_unlock include/linux/rcupdate.h:772 [inline]
__perf_event_output kernel/events/core.c:7813 [inline]
perf_event_output_forward+0x255/0x2e0 kernel/events/core.c:7822
__perf_event_overflow+0x364/0x530 kernel/events/core.c:9515
perf_tp_event+0x383/0xbf0 kernel/events/core.c:10047
perf_trace_run_bpf_submit+0xf3/0x1c0 kernel/events/core.c:10021
perf_trace_preemptirq_template+0x2aa/0x360 include/trace/events/preemptirq.h:14
trace_irq_enable_rcuidle+0x108/0x180 include/trace/events/preemptirq.h:40
trace_hardirqs_on+0x57/0x80 kernel/trace/trace_preemptirq.c:44
asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:713
RIP: 0010:rcu_read_unlock_special+0x7f/0x4a0 kernel/rcu/tree_plugin.h:674
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 f2 cc 9c 7e 41 f7 c6 00 00 f0 00 74 40 <48> c7 44 24 20 0e 36 e0 45 4a c7 04 2b 00 00 00 00 42 c7 44 2b 08
RSP: 0018:ffffc900000077c0 EFLAGS: 00000206
RAX: d141f086f343fb00 RBX: 1ffff92000000efc RCX: d141f086f343fb00
RDX: dffffc0000000000 RSI: ffffffff8a2b3180 RDI: ffffffff8a7a09c0
RBP: ffffc900000078a0 R08: ffffffff901d81c7 R09: 1ffffffff203b038
R10: dffffc0000000000 R11: fffffbfff203b039 R12: ffffffff8c323800
R13: dffffc0000000000 R14: 0000000000000246 R15: 0000000000000001
__rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:422
rcu_read_unlock include/linux/rcupdate.h:772 [inline]
ndisc_send_skb+0xde0/0x1500 net/ipv6/ndisc.c:521
addrconf_rs_timer+0x2d1/0x630 net/ipv6/addrconf.c:3956
call_timer_fn+0x17b/0x540 kernel/time/timer.c:1648
expire_timers kernel/time/timer.c:1699 [inline]
__run_timers+0x53e/0x800 kernel/time/timer.c:1970
run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1983
handle_softirqs+0x339/0x830 kernel/softirq.c:576
__do_softirq kernel/softirq.c:610 [inline]
invoke_softirq kernel/softirq.c:450 [inline]
__irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:put_cpu_partial+0x15e/0x190 mm/slub.c:2591
Code: 00 00 48 3b 44 24 08 75 4d 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 1f 85 ff 07 41 f7 c5 00 02 00 00 74 c3 fb 4d 85 ff <75> c2 eb cb 48 c7 c7 d0 29 3f 8c 4c 89 e6 e8 4f 52 46 02 e9 e5 fe
RSP: 0018:ffffc900030cf648 EFLAGS: 00000286
RAX: d141f086f343fb00 RBX: ffff888016c42140 RCX: d141f086f343fb00
RDX: dffffc0000000000 RSI: ffffffff8a2b3180 RDI: ffffffff8a7a09c0
RBP: 0000000000000001 R08: ffff8880b903b30b R09: 1ffff11017207661
R10: dffffc0000000000 R11: ffffed1017207662 R12: 0000000000000000
R13: 0000000000000286 R14: ffff8880b903e000 R15: ffffea0001d99200
qlist_free_all+0x35/0x90 mm/kasan/quarantine.c:176
kasan_quarantine_reduce+0x150/0x160 mm/kasan/quarantine.c:283
__kasan_kmalloc_large+0x16/0xa0 mm/kasan/common.c:533
kasan_kmalloc_large include/linux/kasan.h:274 [inline]
kmalloc_large_node_hook mm/slub.c:1665 [inline]
kmalloc_large_node+0x12e/0x190 mm/slub.c:4433
__kmalloc_node_track_caller+0x22e/0x3a0 mm/slub.c:4949
kmalloc_reserve net/core/skbuff.c:356 [inline]
__alloc_skb+0x22c/0x750 net/core/skbuff.c:427
alloc_skb include/linux/skbuff.h:1162 [inline]
alloc_skb_with_frags+0xa7/0x730 net/core/skbuff.c:6183
sock_alloc_send_pskb+0x87f/0x9a0 net/core/sock.c:2536
tun_alloc_skb drivers/net/tun.c:1510 [inline]
tun_get_user+0x7c8/0x3a70 drivers/net/tun.c:1822
tun_chr_write_iter+0x112/0x1e0 drivers/net/tun.c:2019
call_write_iter include/linux/fs.h:2173 [inline]
new_sync_write fs/read_write.c:507 [inline]
vfs_write+0x745/0xd60 fs/read_write.c:594
ksys_write+0x152/0x260 fs/read_write.c:647
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f68dff64e59
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:00007f68de1be028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f68e01ddfa0 RCX: 00007f68dff64e59
RDX: 000000000000fdef RSI: 0000200000000580 RDI: 00000000000000c8
RBP: 00007f68dfffae6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f68e01de038 R14: 00007f68e01ddfa0 R15: 00007ffe372605f8
</TASK>


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