INFO: rcu detected stall in tun_chr_close (4)

Status: upstream: reported on 2026/09/27 14:41
Reported-by: syzbot+c4d0b2c340d3ecbd8c4b@syzkaller.appspotmail.com
First crash: 3d18h, last: 3d18h
▶ ▼ Similar bugs (13)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in tun_chr_close (3) netfilter 1 1 2257d 2257d 0/29 auto-closed as invalid on 2020/10/25 04:38
upstream INFO: rcu detected stall in tun_chr_close (7) mm net 1 2 421d 500d 0/29 auto-obsoleted due to no activity on 2025/11/04 06:54
linux-6.1 INFO: rcu detected stall in tun_chr_close 1 1 51d 51d 0/3 upstream: reported on 2026/08/11 00:09
upstream INFO: rcu detected stall in tun_chr_close (2) netfilter 1 1 2397d 2397d 0/29 closed as invalid on 2020/05/30 17:14
upstream INFO: rcu detected stall in tun_chr_close (4) bpf net 1 3 1717d 1787d 0/29 closed as invalid on 2022/02/08 10:00
upstream INFO: rcu detected stall in tun_chr_close net 1 13 2851d 2932d 0/29 auto-closed as invalid on 2019/06/08 11:01
linux-5.15 INFO: rcu detected stall in tun_chr_close (3) 1 1 174d 174d 0/3 auto-obsoleted due to no activity on 2026/07/18 10:54
linux-5.15 INFO: rcu detected stall in tun_chr_close (2) 1 1 754d 754d 0/3 auto-obsoleted due to no activity on 2024/12/15 18:42
linux-5.15 INFO: rcu detected stall in tun_chr_close 1 1 991d 991d 0/3 auto-obsoleted due to no activity on 2024/04/23 00:30
upstream INFO: rcu detected stall in tun_chr_close (5) net 1 1 1215d 1215d 0/29 auto-obsoleted due to no activity on 2023/09/01 17:23
upstream INFO: rcu detected stall in tun_chr_close (6) net mm 1 19 598d 836d 0/29 auto-obsoleted due to no activity on 2025/05/11 04:14
upstream BUG: workqueue lockup (5) prio:low kernel 1 syz, C done 17866 5h14m 2451d 0/29 upstream: reported C repro on 2020/01/14 22:04
android-5-15 BUG: soft lockup in tun_chr_close 1 3 863d 893d 0/2 auto-obsoleted due to no activity on 2024/08/19 06:38

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	0-...!: (1 ticks this GP) idle=277/1/0x4000000000000002 softirq=87486/87486 fqs=0 
	(detected by 1, t=10502 jiffies, g=112973, q=2882)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 32403 Comm: syz.5.5146 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:rcu_read_lock include/linux/rcupdate.h:741 [inline]
RIP: 0010:__perf_output_begin kernel/events/ring_buffer.c:163 [inline]
RIP: 0010:perf_output_begin_forward+0xc4/0xa30 kernel/events/ring_buffer.c:271
Code: 00 e8 e0 a6 c9 ff e8 7b 55 00 00 e8 86 7e 25 08 41 89 c7 31 ff 89 c6 e8 da 5b dd ff 45 85 ff 74 10 e8 d0 f8 c8 ff 84 c0 74 0e <e8> 67 58 dd ff eb 58 e8 60 58 dd ff eb 51 e8 59 7e 25 08 41 89 c7
RSP: 0018:ffffc900000074a0 EFLAGS: 00000002
RAX: 000000000000d201 RBX: ffff888069afbbb0 RCX: 048301827c569100
RDX: 0000000000000100 RSI: ffffffff8a7a48a0 RDI: ffffffff8a7a4860
RBP: ffffc900000075d0 R08: dffffc0000000000 R09: 1ffffffff203e218
R10: dffffc0000000000 R11: fffffbfff203e219 R12: 1ffff92000000ea4
R13: ffffc90000007620 R14: 0000000000000008 R15: 0000000000000001
FS:  000055557cc5c500(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055556aa714e8 CR3: 0000000065047000 CR4: 00000000003506f0
DR0: 0000200000000300 DR1: 0000200000000300 DR2: 0000200000000300
DR3: 0000200000000300 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 __perf_event_output kernel/events/core.c:7814 [inline]
 perf_event_output_forward+0x19b/0x2e0 kernel/events/core.c:7832
 __perf_event_overflow+0x35f/0x550 kernel/events/core.c:9525
 perf_swevent_overflow kernel/events/core.c:9601 [inline]
 perf_swevent_event+0x4b8/0x540 kernel/events/core.c:9639
 perf_tp_event+0x324/0xbe0 kernel/events/core.c:10057
 perf_trace_run_bpf_submit+0xf3/0x1c0 kernel/events/core.c:10031
 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 42 0b 9d 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:ffffc90000007c60 EFLAGS: 00000206
RAX: 048301827c569100 RBX: 1ffff92000000f90 RCX: 048301827c569100
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a48c0
RBP: ffffc90000007d30 R08: ffffffff901f10cf R09: 1ffffffff203e219
R10: dffffc0000000000 R11: fffffbfff203e21a R12: ffffffff8c323400
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]
 rebalance_domains+0x88d/0x9b0 kernel/sched/fair.c:10660
 handle_softirqs+0x336/0x830 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:should_resched arch/x86/include/asm/preempt.h:103 [inline]
RIP: 0010:__local_bh_enable_ip+0x13e/0x1c0 kernel/softirq.c:408
Code: 8a e8 66 0e 78 08 65 66 8b 05 4e 61 ba 7e 66 85 c0 75 54 bf 01 00 00 00 e8 cf 21 09 00 e8 aa 08 36 00 fb 65 8b 05 fa 37 b9 7e <85> c0 75 05 e8 39 45 b7 ff 48 c7 04 24 0e 36 e0 45 4b c7 04 37 00
RSP: 0018:ffffc90002f2f860 EFLAGS: 00000286
RAX: 0000000080000000 RBX: 0000000000000201 RCX: 048301827c569100
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a48c0
RBP: ffffc90002f2f8f8 R08: ffffffff901f10cf R09: 1ffffffff203e219
R10: dffffc0000000000 R11: fffffbfff203e21a R12: ffffffff880559a4
R13: 0000000000000004 R14: dffffc0000000000 R15: 1ffff920005e5f0c
 spin_unlock_bh include/linux/spinlock.h:409 [inline]
 some_qdisc_is_busy net/sched/sch_generic.c:1280 [inline]
 dev_deactivate_many+0xa54/0xc00 net/sched/sch_generic.c:1325
 __dev_close_many+0x164/0x2b0 net/core/dev.c:1621
 dev_close_many+0x21c/0x400 net/core/dev.c:1659
 unregister_netdevice_many+0x4b8/0x1a40 net/core/dev.c:11136
 unregister_netdevice_queue+0x2e1/0x320 net/core/dev.c:11093
 unregister_netdevice include/linux/netdevice.h:3047 [inline]
 __tun_detach+0xdb7/0x1580 drivers/net/tun.c:686
 tun_detach drivers/net/tun.c:702 [inline]
 tun_chr_close+0x109/0x1b0 drivers/net/tun.c:3454
 __fput+0x212/0x8c0 fs/file_table.c:311
 task_work_run+0x125/0x1a0 kernel/task_work.c:188
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop+0x10f/0x130 kernel/entry/common.c:184
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:217
 __syscall_exit_to_user_mode_work kernel/entry/common.c:299 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:310
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7ff3c6b7a159
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:00007ffc7dbef488 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007ff3c6e03da0 RCX: 00007ff3c6b7a159
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007ff3c6e03da0 R08: 0000000000000006 R09: 0000000000000000
R10: 00007ff3c6e03cb0 R11: 0000000000000246 R12: 0000000000113b64
R13: 00007ff3c6e01fac R14: 00000000001139ce R15: 00007ffc7dbef590
 </TASK>
rcu: rcu_preempt kthread timer wakeup didn't happen for 10501 jiffies! g112973 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
rcu: 	Possible timer handling issue on cpu=0 timer-softirq=52800
rcu: rcu_preempt kthread starved for 10502 jiffies! g112973 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=0
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:I stack:27536 pid:   15 ppid:     2 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11c3/0x4350 kernel/sched/core.c:6395
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 schedule_timeout+0x184/0x2d0 kernel/time/timer.c:2117
 rcu_gp_fqs_loop+0x2be/0x11f0 kernel/rcu/tree.c:1972
 rcu_gp_kthread+0x9a/0x370 kernel/rcu/tree.c:2145
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 32403 Comm: syz.5.5146 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:check_kcov_mode kernel/kcov.c:171 [inline]
RIP: 0010:__sanitizer_cov_trace_pc+0x2a/0x60 kernel/kcov.c:205
Code: 48 8b 04 24 65 48 8b 0d 14 5b 89 7e 65 8b 15 15 5b 89 7e 81 e2 00 01 ff 00 74 11 81 fa 00 01 00 00 75 35 83 b9 34 16 00 00 00 <74> 2c 8b 91 10 16 00 00 83 fa 02 75 21 48 8b 91 18 16 00 00 48 8b
RSP: 0018:ffffc90000007490 EFLAGS: 00000046
RAX: ffffffff8197abe8 RBX: 0000000000000000 RCX: ffff888027e53b80
RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000000
RBP: dffffc0000000000 R08: ffffc90000007657 R09: ffffc90000007620
R10: dffffc0000000000 R11: fffff52000000ecb R12: ffff88803bdcc302
R13: ffffc90000007840 R14: ffff88803bdcc1a8 R15: ffffc90000007686
FS:  000055557cc5c500(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055556aa714e8 CR3: 0000000065047000 CR4: 00000000003506f0
DR0: 0000200000000300 DR1: 0000200000000300 DR2: 0000200000000300
DR3: 0000200000000300 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 __perf_event_header__init_id+0x368/0x4f0 kernel/events/core.c:7122
 perf_prepare_sample+0x158/0x1cb0 kernel/events/core.c:7634
 __perf_event_output kernel/events/core.c:7812 [inline]
 perf_event_output_forward+0x185/0x2e0 kernel/events/core.c:7832
 __perf_event_overflow+0x35f/0x550 kernel/events/core.c:9525
 perf_swevent_overflow kernel/events/core.c:9601 [inline]
 perf_swevent_event+0x4b8/0x540 kernel/events/core.c:9639
 perf_tp_event+0x324/0xbe0 kernel/events/core.c:10057
 perf_trace_run_bpf_submit+0xf3/0x1c0 kernel/events/core.c:10031
 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 42 0b 9d 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:ffffc90000007c60 EFLAGS: 00000206
RAX: 048301827c569100 RBX: 1ffff92000000f90 RCX: 048301827c569100
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a48c0
RBP: ffffc90000007d30 R08: ffffffff901f10cf R09: 1ffffffff203e219
R10: dffffc0000000000 R11: fffffbfff203e21a R12: ffffffff8c323400
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]
 rebalance_domains+0x88d/0x9b0 kernel/sched/fair.c:10660
 handle_softirqs+0x336/0x830 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:should_resched arch/x86/include/asm/preempt.h:103 [inline]
RIP: 0010:__local_bh_enable_ip+0x13e/0x1c0 kernel/softirq.c:408
Code: 8a e8 66 0e 78 08 65 66 8b 05 4e 61 ba 7e 66 85 c0 75 54 bf 01 00 00 00 e8 cf 21 09 00 e8 aa 08 36 00 fb 65 8b 05 fa 37 b9 7e <85> c0 75 05 e8 39 45 b7 ff 48 c7 04 24 0e 36 e0 45 4b c7 04 37 00
RSP: 0018:ffffc90002f2f860 EFLAGS: 00000286
RAX: 0000000080000000 RBX: 0000000000000201 RCX: 048301827c569100
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a48c0
RBP: ffffc90002f2f8f8 R08: ffffffff901f10cf R09: 1ffffffff203e219
R10: dffffc0000000000 R11: fffffbfff203e21a R12: ffffffff880559a4
R13: 0000000000000004 R14: dffffc0000000000 R15: 1ffff920005e5f0c
 spin_unlock_bh include/linux/spinlock.h:409 [inline]
 some_qdisc_is_busy net/sched/sch_generic.c:1280 [inline]
 dev_deactivate_many+0xa54/0xc00 net/sched/sch_generic.c:1325
 __dev_close_many+0x164/0x2b0 net/core/dev.c:1621
 dev_close_many+0x21c/0x400 net/core/dev.c:1659
 unregister_netdevice_many+0x4b8/0x1a40 net/core/dev.c:11136
 unregister_netdevice_queue+0x2e1/0x320 net/core/dev.c:11093
 unregister_netdevice include/linux/netdevice.h:3047 [inline]
 __tun_detach+0xdb7/0x1580 drivers/net/tun.c:686
 tun_detach drivers/net/tun.c:702 [inline]
 tun_chr_close+0x109/0x1b0 drivers/net/tun.c:3454
 __fput+0x212/0x8c0 fs/file_table.c:311
 task_work_run+0x125/0x1a0 kernel/task_work.c:188
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop+0x10f/0x130 kernel/entry/common.c:184
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:217
 __syscall_exit_to_user_mode_work kernel/entry/common.c:299 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:310
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7ff3c6b7a159
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:00007ffc7dbef488 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007ff3c6e03da0 RCX: 00007ff3c6b7a159
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007ff3c6e03da0 R08: 0000000000000006 R09: 0000000000000000
R10: 00007ff3c6e03cb0 R11: 0000000000000246 R12: 0000000000113b64
R13: 00007ff3c6e01fac R14: 00000000001139ce R15: 00007ffc7dbef590
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/27 14:41 linux-5.15.y 0248c33e835e a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in tun_chr_close
* Struck through repros no longer work on HEAD.