INFO: rcu detected stall in __tun_chr_ioctl (2)

Status: upstream: reported on 2026/07/02 11:58
Reported-by: syzbot+8b4ff2a7f5a77cb64934@syzkaller.appspotmail.com
First crash: 101d, last: 21d
▶ ▼ Similar bugs (7)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in __tun_chr_ioctl mm 1 4 632d 707d 0/29 auto-obsoleted due to no activity on 2025/04/18 05:25
linux-5.15 INFO: rcu detected stall in __tun_chr_ioctl 1 1 584d 584d 0/3 auto-obsoleted due to no activity on 2025/06/14 12:09
linux-6.1 INFO: rcu detected stall in __tun_chr_ioctl 1 3 299d 323d 0/3 auto-obsoleted due to no activity on 2026/03/26 13:49
linux-6.6 INFO: rcu detected stall in __tun_chr_ioctl 1 1 203d 203d 0/2 auto-obsoleted due to no activity on 2026/07/01 00:03
linux-6.1 INFO: rcu detected stall in __tun_chr_ioctl (2) 1 8 26d 197d 0/3 upstream: reported on 2026/03/28 18:58
upstream INFO: rcu detected stall in __tun_chr_ioctl (2) prio:normal mm 1 34 15d 44d 0/29 closed as invalid on 2026/10/06 02:14
linux-5.15 INFO: rcu detected stall in __tun_chr_ioctl (2) 1 24 5d05h 322d 0/3 upstream: reported on 2025/11/23 13:35

Sample crash report:
rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-....: (1 GPs behind) idle=1484/1/0x4000000000000000 softirq=11026/11028 fqs=129
rcu: 	         hardirqs   softirqs   csw/system
rcu: 	 number:  1711260          5            0
rcu: 	cputime:    38069       4231           14   ==> 42330(ms)
rcu: 	(t=10503 jiffies g=9849 q=1218 ncpus=2)
CPU: 1 PID: 5892 Comm: syz.1.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:neigh_event_send_probe include/net/neighbour.h:462 [inline]
RIP: 0010:neigh_event_send include/net/neighbour.h:473 [inline]
RIP: 0010:neigh_resolve_output+0x2a/0x710 net/core/neighbour.c:1552
Code: f3 0f 1e fa 55 41 57 41 56 41 55 41 54 53 48 81 ec 90 00 00 00 48 89 f3 49 89 fe 49 bd 00 00 00 00 00 fc ff df e8 56 f4 fe f8 <48> c7 c0 00 f2 e0 8c 48 c1 e8 03 42 80 3c 28 00 74 0c 48 c7 c7 00
RSP: 0018:ffffc900001f06b8 EFLAGS: 00000246
RAX: ffffffff888896fa RBX: ffff888030f4d000 RCX: ffff88802d0cbc00
RDX: 0000000000000100 RSI: ffff888030f4d000 RDI: ffff88802c3e8800
RBP: ffffc900001f08b0 R08: ffffffff911eb607 R09: 1ffffffff223d6c0
R10: dffffc0000000000 R11: fffffbfff223d6c1 R12: ffff888030f4d000
R13: dffffc0000000000 R14: ffff88802c3e8800 R15: dffffc0000000000
FS:  00007feab67f66c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f95ac5eb840 CR3: 00000000793b9000 CR4: 00000000003506e0
Call Trace:
 <IRQ>
 neigh_output include/net/neighbour.h:547 [inline]
 ip6_finish_output2+0xf7a/0x1690 net/ipv6/ip6_output.c:143
 dst_output include/net/dst.h:470 [inline]
 NF_HOOK include/linux/netfilter.h:304 [inline]
 ndisc_send_skb+0xbb9/0x1480 net/ipv6/ndisc.c:513
 addrconf_rs_timer+0x36b/0x640 net/ipv6/addrconf.c:4036
 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:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xc0/0x120 kernel/locking/spinlock.c:194
Code: c7 44 24 20 00 00 00 00 9c 8f 44 24 20 f7 44 24 20 00 02 00 00 41 c6 04 07 f8 75 4b f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> 3b f7 c1 f6 65 8b 05 ec b4 68 75 85 c0 74 3c 48 c7 04 24 0e 36
RSP: 0018:ffffc90004d67580 EFLAGS: 00000206
RAX: dffffc0000000004 RBX: 0000000000000a02 RCX: 404831e3703c8600
RDX: dffffc0000000000 RSI: ffffffff8acacce0 RDI: 0000000000000001
RBP: ffffc90004d67608 R08: ffffffff911eb52f R09: 1ffffffff223d6a5
R10: dffffc0000000000 R11: fffffbfff223d6a6 R12: dffffc0000000000
R13: ffff88803004c000 R14: ffffffff9753d0c0 R15: 1ffff920009aceb0
 __debug_check_no_obj_freed lib/debugobjects.c:1054 [inline]
 debug_check_no_obj_freed+0x47b/0x520 lib/debugobjects.c:1075
 free_pages_prepare mm/page_alloc.c:1188 [inline]
 free_unref_page_prepare+0x1ed/0x8f0 mm/page_alloc.c:2366
 free_unref_page+0x32/0x2e0 mm/page_alloc.c:2459
 __slab_free+0x35a/0x400 mm/slub.c:3736
 qlink_free mm/kasan/quarantine.c:166 [inline]
 qlist_free_all+0x75/0xd0 mm/kasan/quarantine.c:185
 kasan_quarantine_reduce+0x143/0x160 mm/kasan/quarantine.c:292
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:306
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6a/0x4d0 mm/slab.h:770
 slab_alloc_node mm/slub.c:3495 [inline]
 __kmem_cache_alloc_node+0x194/0x250 mm/slub.c:3534
 kmalloc_trace+0x2a/0xe0 mm/slab_common.c:1098
 kmalloc include/linux/slab.h:600 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 ref_tracker_alloc+0x163/0x4b0 lib/ref_tracker.c:203
 __netdev_tracker_alloc include/linux/netdevice.h:4159 [inline]
 netdev_hold include/linux/netdevice.h:4188 [inline]
 rx_queue_add_kobject net/core/net-sysfs.c:1083 [inline]
 net_rx_queue_update_kobjects+0x172/0x590 net/core/net-sysfs.c:1141
 register_queue_kobjects net/core/net-sysfs.c:1801 [inline]
 netdev_register_kobject+0x235/0x320 net/core/net-sysfs.c:2046
 register_netdevice+0x12aa/0x1ba0 net/core/dev.c:10342
 tun_set_iff+0x82b/0xea0 drivers/net/tun.c:2876
 __tun_chr_ioctl+0x7e0/0x2070 drivers/net/tun.c:3145
 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: 0033:0x7feab859e159
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:00007feab67f6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007feab8825fa0 RCX: 00007feab859e159
RDX: 0000200000000040 RSI: 00000000400454ca RDI: 0000000000000005
RBP: 00007feab863506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007feab8826038 R14: 00007feab8825fa0 R15: 00007ffdd88e3db8
 </TASK>

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/21 06:31 linux-6.6.y 79643295eba1 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in __tun_chr_ioctl
2026/07/09 04:20 linux-6.6.y da47cbc25466 b9f1ceaa .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in __tun_chr_ioctl
2026/07/02 11:57 linux-6.6.y d1cfde2d5d15 27192279 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in __tun_chr_ioctl
* Struck through repros no longer work on HEAD.