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: 85d, last: 23h33m
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 519d 594d 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 472d 472d 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 187d 211d 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 91d 91d 0/2 upstream: reported on 2026/03/23 00:03
linux-5.15 INFO: rcu detected stall in __tun_chr_ioctl (2) 1 11 14d 210d 0/3 upstream: reported on 2025/11/23 13:35

Sample crash report:
rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 0-.... } 2691 jiffies s: 316969 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: 26423 Comm: syz.3.5828 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:native_save_fl arch/x86/include/asm/irqflags.h:29 [inline]
RIP: 0010:arch_local_save_flags arch/x86/include/asm/irqflags.h:70 [inline]
RIP: 0010:lockdep_hardirqs_off+0x45/0x100 kernel/locking/lockdep.c:4407
Code: 00 0f 84 90 00 00 00 48 89 fb 65 8b 05 8c 93 d7 75 a9 00 00 f0 00 74 68 83 3d 76 b5 94 0c 00 75 15 48 c7 04 24 00 00 00 00 9c <8f> 04 24 f7 04 24 00 02 00 00 75 79 65 8b 05 88 9a d7 75 85 c0 74
RSP: 0018:ffffc90000007d20 EFLAGS: 00000046
RAX: 0000000000000000 RBX: ffffffff8a2ab8da RCX: 4d61b8f15aafab00
RDX: 0000000000000000 RSI: ffffffff8a8c17c0 RDI: ffffffff8adee1a0
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS:  00007ff93fdf36c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f14cd808ff8 CR3: 0000000058fb6000 CR4: 00000000003506f0
DR0: 0000200000000300 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 irqentry_enter+0x27/0x50 kernel/entry/common.c:-1
 sysvec_irq_work+0xa/0xc0 arch/x86/kernel/irq_work.c:17
 asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:728
RIP: 0010:variable_ffs arch/x86/include/asm/bitops.h:319 [inline]
RIP: 0010:handle_softirqs+0x1b7/0x910 kernel/softirq.c:584
Code: 89 7c 24 2c 0f b7 db 48 c7 c7 80 0d 8b 8a e8 e0 af db 08 65 66 c7 05 66 62 b4 7e 00 00 e8 b1 47 39 00 fb 49 c7 c5 c0 a0 80 8c <89> 5c 24 34 b8 ff ff ff ff 0f bc 44 24 34 41 89 c6 41 ff c6 0f 84
RSP: 0018:ffffc90000007e20 EFLAGS: 00000282
RAX: 4d61b8f15aafab00 RBX: 0000000000000200 RCX: 4d61b8f15aafab00
RDX: dffffc0000000000 RSI: ffffffff8a8c17a0 RDI: ffffffff8adee1a0
RBP: ffffc90000007f30 R08: ffffffff90af224f R09: 1ffffffff215e449
R10: dffffc0000000000 R11: fffffbfff215e44a R12: dffffc0000000000
R13: ffffffff8c80a0c0 R14: ffff88802d0b1e00 R15: 000000000000000a
 __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:rcu_read_unlock_special+0x65/0x510 kernel/rcu/tree_plugin.h:630
Code: 41 48 c7 44 24 48 d3 60 40 8c 48 c7 44 24 50 f0 eb 6c 81 48 8d 5c 24 40 48 c1 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 e2 82 95 7e 41 f7 c6 00 00
RSP: 0018:ffffc900033e73e0 EFLAGS: 00000a06
RAX: f2f2f2f8f1f1f1f1 RBX: 1ffff9200067ce84 RCX: 0000000000080000
RDX: ffffc900139ed000 RSI: 000000000006e462 RDI: ffff88802d0b1e00
RBP: ffffc900033e74d8 R08: ffff88801b41123f R09: 1ffff11003682247
R10: dffffc0000000000 R11: ffffed1003682248 R12: 1ffff11005a16447
R13: dffffc0000000000 R14: ffff88802d0b2240 R15: dffffc0000000000
 __rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:426
 rcu_read_unlock include/linux/rcupdate.h:823 [inline]
 page_ext_put+0x91/0xb0 mm/page_ext.c:182
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1487 [inline]
 free_pcp_prepare mm/page_alloc.c:1537 [inline]
 free_unref_page_prepare+0x8e5/0x9e0 mm/page_alloc.c:3414
 free_unref_page+0x2e/0x3f0 mm/page_alloc.c:3509
 free_slab mm/slub.c:2036 [inline]
 discard_slab mm/slub.c:2042 [inline]
 __unfreeze_partials+0x188/0x1e0 mm/slub.c:2591
 put_cpu_partial+0x17c/0x250 mm/slub.c:2667
 qlink_free mm/kasan/quarantine.c:168 [inline]
 qlist_free_all+0x76/0xe0 mm/kasan/quarantine.c:187
 kasan_quarantine_reduce+0x144/0x160 mm/kasan/quarantine.c:294
 __kasan_slab_alloc+0x1e/0x80 mm/kasan/common.c:306
 kasan_slab_alloc include/linux/kasan.h:201 [inline]
 slab_post_alloc_hook+0x4b/0x490 mm/slab.h:737
 slab_alloc_node mm/slub.c:3359 [inline]
 slab_alloc mm/slub.c:3367 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3374 [inline]
 kmem_cache_alloc+0x18b/0x2f0 mm/slub.c:3383
 kmem_cache_zalloc include/linux/slab.h:689 [inline]
 __kernfs_new_node+0xe1/0x7f0 fs/kernfs/dir.c:614
 kernfs_new_node+0x148/0x250 fs/kernfs/dir.c:690
 kernfs_create_dir_ns+0x40/0x120 fs/kernfs/dir.c:1046
 internal_create_group+0x21a/0xce0 fs/sysfs/group.c:136
 dpm_sysfs_add+0x66/0x270 drivers/base/power/sysfs.c:702
 device_add+0x745/0x1050 drivers/base/core.c:3654
 netdev_register_kobject+0x184/0x320 net/core/net-sysfs.c:2013
 register_netdevice+0x133a/0x1b80 net/core/dev.c:10243
 tun_set_iff+0x82b/0xea0 drivers/net/tun.c:2854
 __tun_chr_ioctl+0x770/0x1ed0 drivers/net/tun.c:3117
 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: 0033:0x7ff93ef9ce59
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:00007ff93fdf3028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007ff93f215fa0 RCX: 00007ff93ef9ce59
RDX: 0000200000000140 RSI: 00000000400454ca RDI: 0000000000000003
RBP: 00007ff93f032e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff93f216038 R14: 00007ff93f215fa0 R15: 00007fffadf9f4b8
 </TASK>

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/06/21 03:24 linux-6.1.y fdb6fcb41cc7 43bfcdb0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-perf INFO: rcu detected stall in __tun_chr_ioctl
2026/06/13 06:25 linux-6.1.y 228da13e907e 1d2f3589 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-perf INFO: rcu detected stall in __tun_chr_ioctl
2026/05/13 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.