syzbot


INFO: rcu detected stall in __tun_chr_ioctl (2)

Status: upstream: reported on 2026/03/28 18:58
Reported-by: syzbot+d77d02a11256ce87187c@syzkaller.appspotmail.com
First crash: 27d, last: 5d21h
Similar bugs (5)
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 461d 536d 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 414d 414d 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 129d 153d 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 32d 32d 0/2 upstream: reported on 2026/03/23 00:03
linux-5.15 INFO: rcu detected stall in __tun_chr_ioctl (2) 1 9 24d 152d 0/3 upstream: reported on 2025/11/23 13:35

Sample crash report:
rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 1-.... } 2685 jiffies s: 177957 root: 0x2/.
rcu: blocking rcu_node structures (internal RCU debug):
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 12466 Comm: syz.4.12116 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
RIP: 0010:kasan_check_range+0x1b2/0x290 mm/kasan/generic.c:-1
Code: 01 f3 49 89 df 49 8d 5f 07 4d 85 ff 49 0f 49 df 48 83 e3 f8 49 29 df 74 0e 41 80 3b 00 75 69 49 ff c3 49 ff cf 75 f2 5b 41 5c <41> 5e 41 5f 5d c3 45 84 ff 0f 85 91 00 00 00 41 f7 c7 00 ff 00 00
RSP: 0018:ffffc900001e05a0 EFLAGS: 00000056
RAX: 1ffff110171e6801 RBX: ffff8880b8f340f8 RCX: ffffffff818ed26e
RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffff8880b8f340f8
RBP: ffffc900001e0670 R08: ffff8880b8f340ff R09: 1ffff110171e681f
R10: dffffc0000000000 R11: ffffed10171e6820 R12: 1ffff9200003c0b8
R13: 0000000000000000 R14: 1ffff110171e681f R15: 0000000000000001
FS:  00007f7207da96c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f85a6de7158 CR3: 0000000053550000 CR4: 00000000003506e0
DR0: 0000200000000300 DR1: 0000200000000300 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 instrument_atomic_write include/linux/instrumented.h:87 [inline]
 llist_del_all include/linux/llist.h:239 [inline]
 irq_work_run_list kernel/irq_work.c:240 [inline]
 irq_work_run+0x11e/0x2f0 kernel/irq_work.c:251
 __sysvec_irq_work+0xba/0x350 arch/x86/kernel/irq_work.c:22
 instr_sysvec_irq_work arch/x86/kernel/irq_work.c:17 [inline]
 sysvec_irq_work+0x4a/0xc0 arch/x86/kernel/irq_work.c:17
 asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:728
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:ffffc900001e0760 EFLAGS: 00000206
RAX: 6aef1516d0804a00 RBX: 1ffff9200003c0f4 RCX: 6aef1516d0804a00
RDX: dffffc0000000000 RSI: ffffffff8a8c1120 RDI: ffffffff8adf13a0
RBP: ffffc900001e0860 R08: ffffffff90af9337 R09: 1ffffffff215f266
R10: dffffc0000000000 R11: fffffbfff215f267 R12: 0000000000000246
R13: dffffc0000000000 R14: ffff8880b8f3b900 R15: 0000000000000002
 __rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:426
 rcu_read_unlock include/linux/rcupdate.h:823 [inline]
 ndisc_send_skb+0xd9d/0x14e0 net/ipv6/ndisc.c:521
 addrconf_rs_timer+0x2d1/0x630 net/ipv6/addrconf.c:3979
 call_timer_fn+0x1ac/0x670 kernel/time/timer.c:1701
 expire_timers kernel/time/timer.c:1752 [inline]
 __run_timers+0x53e/0x800 kernel/time/timer.c:2023
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:2036
 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:notifier_call_chain kernel/notifier.c:75 [inline]
RIP: 0010:raw_notifier_call_chain+0x36/0x160 kernel/notifier.c:455
Code: ec 18 48 89 54 24 10 48 89 74 24 08 49 89 ff 49 bd 00 00 00 00 00 fc ff df e8 06 28 2b 00 4c 89 f8 48 c1 e8 03 42 80 3c 28 00 <74> 08 4c 89 ff e8 30 34 7c 00 4d 8b 27 4d 85 e4 0f 84 e2 00 00 00
RSP: 0018:ffffc90005797b50 EFLAGS: 00000246
RAX: 1ffffffff2e03c04 RBX: 1ffff92000af2f84 RCX: 0000000000080000
RDX: ffffc900112aa000 RSI: 000000000000360d RDI: 000000000000360e
RBP: ffffc90005797d00 R08: ffff88805bc1d940 R09: 0000000000000005
R10: 0000000000000026 R11: 0000000000000002 R12: dffffc0000000000
R13: dffffc0000000000 R14: ffff888062f54000 R15: ffffffff9701e020
 call_netdevice_notifiers_extack net/core/dev.c:2052 [inline]
 call_netdevice_notifiers net/core/dev.c:2066 [inline]
 register_netdevice+0x128c/0x1b10 net/core/dev.c:10238
 tun_set_iff+0x848/0xed0 drivers/net/tun.c:2851
 __tun_chr_ioctl+0x781/0x1e60 drivers/net/tun.c:3114
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
 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: 0033:0x7f7206f9c819
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:00007f7207da9028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f7207215fa0 RCX: 00007f7206f9c819
RDX: 0000200000000040 RSI: 00000000400454ca RDI: 0000000000000006
RBP: 00007f7207032c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7207216038 R14: 00007f7207215fa0 R15: 00007ffd2d7f9c98
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/04/18 21:34 linux-6.1.y 7c87defbd336 303e2802 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-perf INFO: rcu detected stall in __tun_chr_ioctl
2026/03/28 18:58 linux-6.1.y 1989cd3d56e2 b5ceaad2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-perf INFO: rcu detected stall in __tun_chr_ioctl
* Struck through repros no longer work on HEAD.