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: 47d, last: 1d09h
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 481d 556d 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 434d 434d 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 149d 173d 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 53d 53d 0/2 upstream: reported on 2026/03/23 00:03
linux-5.15 INFO: rcu detected stall in __tun_chr_ioctl (2) 1 10 16d 172d 0/3 upstream: reported on 2025/11/23 13:35

Sample crash report:
rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 0-.... } 2656 jiffies s: 36965 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: 13677 Comm: syz.0.2970 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:trace_irq_enable_rcuidle+0xbb/0x140 include/trace/events/preemptirq.h:40
Code: b7 8c e8 68 2b e3 ff 89 c5 e8 01 f3 21 00 4c 8b 3d 1a fe 82 0c 4d 85 ff 74 28 49 83 c7 08 4c 89 f8 48 c1 e8 03 42 80 3c 20 00 <74> 08 4c 89 ff e8 2b a2 4a 00 49 8b 3f 4c 89 f6 48 89 da e8 2d fa
RSP: 0018:ffffc900000079d8 EFLAGS: 00000046
RAX: 1ffff1100471fd03 RBX: 0000000000000000 RCX: ffff88801eab3b80
RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000001 R08: ffff8880b8e3580b R09: 1ffff110171c6b01
R10: dffffc0000000000 R11: ffffed10171c6b02 R12: dffffc0000000000
R13: 0000000000000000 R14: ffffffff8a400e86 R15: ffff8880238fe818
FS:  00007f1a9dbb36c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f876d2a0000 CR3: 000000002776d000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000200000000300 DR2: 0000200000000300
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 trace_hardirqs_on+0x24/0x40 kernel/trace/trace_preemptirq.c:44
 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:ffffc90000007ac0 EFLAGS: 00000206
RAX: 4a2c8d63fc2bdb00 RBX: 1ffff92000000f60 RCX: 4a2c8d63fc2bdb00
RDX: dffffc0000000000 RSI: ffffffff8a8c1120 RDI: ffffffff8adf1320
RBP: ffffc90000007bb0 R08: ffffffff90af924f R09: 1ffffffff215f249
R10: dffffc0000000000 R11: fffffbfff215f24a R12: 0000000000000246
R13: dffffc0000000000 R14: ffff8880b8e3b900 R15: 0000000000000001
 __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:rwsem_write_trylock+0x0/0x1c0 kernel/locking/rwsem.c:257
Code: 03 02 00 00 00 75 02 5b c3 48 89 df be 08 00 00 00 e8 64 b4 6f 00 f0 48 83 23 fd 5b c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 <55> 48 89 e5 41 57 41 56 41 55 41 54 53 48 83 e4 e0 48 83 ec 60 48
RSP: 0018:ffffc900038cf778 EFLAGS: 00000292
RAX: 4a2c8d63fc2bdb00 RBX: ffff8880174734d8 RCX: 4a2c8d63fc2bdb00
RDX: 0000000000000000 RSI: ffffffff8a8c22a0 RDI: ffff8880174734d8
RBP: ffffffff8d54eea0 R08: dffffc0000000000 R09: 1ffffffff215f249
R10: dffffc0000000000 R11: fffffbfff215f24a R12: dffffc0000000000
R13: ffff8881452f26d0 R14: ffff8880174734d8 R15: ffff888053830d98
 __down_write_common kernel/locking/rwsem.c:1313 [inline]
 __down_write kernel/locking/rwsem.c:1323 [inline]
 down_write+0x42/0x60 kernel/locking/rwsem.c:1574
 kernfs_add_one+0x95/0x8f0 fs/kernfs/dir.c:768
 __kernfs_create_file+0x233/0x2e0 fs/kernfs/file.c:1097
 sysfs_add_file_mode_ns+0x234/0x2f0 fs/sysfs/file.c:294
 create_files fs/sysfs/group.c:64 [inline]
 internal_create_group+0x493/0xcf0 fs/sysfs/group.c:148
 internal_create_groups fs/sysfs/group.c:188 [inline]
 sysfs_create_groups+0x55/0x120 fs/sysfs/group.c:214
 device_add_groups drivers/base/core.c:2752 [inline]
 device_add_attrs+0x1ae/0x830 drivers/base/core.c:2911
 device_add+0x64b/0xfb0 drivers/base/core.c:3648
 netdev_register_kobject+0x184/0x320 net/core/net-sysfs.c:2013
 register_netdevice+0x12dc/0x1b10 net/core/dev.c:10243
 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: 0033:0x7f1a9cd9ce59
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:00007f1a9dbb3028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f1a9d016090 RCX: 00007f1a9cd9ce59
RDX: 0000200000000000 RSI: 00000000400454ca RDI: 0000000000000006
RBP: 00007f1a9ce32d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1a9d016128 R14: 00007f1a9d016090 R15: 00007ffede620688
 </TASK>

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/05/13 16:16 linux-6.1.y ad16b162f21d fec2a7ee .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-perf INFO: rcu detected stall in __tun_chr_ioctl
2026/04/18 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.