[v6.6] INFO: rcu detected stall in tun_chr_write_iter
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syzbot
Jul 2, 2026, 7:03:30 PM (2 days ago) Jul 2
to syzkaller...@googlegroups.com
Hello,
syzbot found the following issue on:
HEAD commit: d1cfde2d5d15 Linux 6.6.143
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=15f52c0a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=938110aa66424b94
dashboard link: https://syzkaller.appspot.com/bug?extid=b5fe56e1db1079d6c11e
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/fb0f102e0a80/disk-d1cfde2d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/928fc5f681d8/vmlinux-d1cfde2d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fc3e26207ef8/bzImage-d1cfde2d.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b5fe56...@syzkaller.appspotmail.com
rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 1-....: (10498 ticks this GP) idle=8024/1/0x4000000000000000 softirq=53835/53836 fqs=3107
rcu: hardirqs softirqs csw/system
rcu: number: 906373 0 0
rcu: cputime: 8706 18272 19 ==> 26980(ms)
rcu: (t=10500 jiffies g=63853 q=627 ncpus=2)
CPU: 1 PID: 15098 Comm: syz.3.3241 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:lock_is_held_type+0x13e/0x190 kernel/locking/lockdep.c:5830
Code: 75 40 48 c7 04 24 00 00 00 00 9c 8f 04 24 f7 04 24 00 02 00 00 75 46 41 f7 c5 00 02 00 00 74 01 fb 65 48 8b 04 25 28 00 00 00 <48> 3b 44 24 08 75 3c 89 e8 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f
RSP: 0018:ffffc900001f0328 EFLAGS: 00000206
RAX: c4e772bc0b111600 RBX: ffff888018fcda00 RCX: c4e772bc0b111600
RDX: 0000000000000100 RSI: ffffffff8acadce0 RDI: ffffffff8b1cf820
RBP: 0000000000000000 R08: ffff888018fcda00 R09: 000000000000000b
R10: 000000000000000a R11: 0000000000000100 R12: 0000000000000007
R13: 0000000000000246 R14: ffffffff8e3d5f88 R15: ffff888018fce5f8
FS: 00007f05635086c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000100000000 CR3: 0000000076d31000 CR4: 00000000003506e0
DR0: 0000200000000300 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
<IRQ>
lock_is_held include/linux/lockdep.h:288 [inline]
lockdep_rtnl_is_held+0x1b/0x30 net/core/rtnetlink.c:176
__in6_dev_get include/net/addrconf.h:323 [inline]
ipv6_dev_get_saddr+0x256/0xbb0 net/ipv6/addrconf.c:1866
ip6_route_get_saddr include/net/ip6_route.h:148 [inline]
ip6_dst_lookup_tail+0x107e/0x1660 net/ipv6/ip6_output.c:1138
icmpv6_route_lookup+0xfe/0x600 net/ipv6/icmp.c:363
icmp6_send+0x11b0/0x1b60 net/ipv6/icmp.c:604
__icmpv6_send include/linux/icmpv6.h:28 [inline]
icmpv6_send include/linux/icmpv6.h:49 [inline]
ip6_link_failure+0x3b/0x4c0 net/ipv6/route.c:2839
dst_link_failure include/net/dst.h:437 [inline]
ndisc_error_report+0x112/0x160 net/ipv6/ndisc.c:733
neigh_invalidate+0x23b/0x460 net/core/neighbour.c:1064
neigh_timer_handler+0x911/0xff0 net/core/neighbour.c:1151
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:preempt_schedule_irq+0xba/0x150 kernel/sched/core.c:7010
Code: 00 00 43 c6 44 37 04 f8 74 0b 0f 0b 48 f7 03 08 00 00 00 74 6f bf 01 00 00 00 e8 51 81 c8 f6 e8 8c 6d f9 f6 fb bf 01 00 00 00 <e8> 31 b4 ff ff 43 c6 44 37 08 00 48 c7 44 24 40 00 00 00 00 9c 8f
RSP: 0018:ffffc9000b4b7420 EFLAGS: 00000282
RAX: c4e772bc0b111600 RBX: 0000000000000000 RCX: c4e772bc0b111600
RDX: dffffc0000000000 RSI: ffffffff8acacb60 RDI: 0000000000000001
RBP: ffffc9000b4b74d0 R08: ffffffff911e752f R09: 1ffffffff223cea5
R10: dffffc0000000000 R11: fffffbfff223cea6 R12: 0000000000000000
R13: 0000000000000000 R14: dffffc0000000000 R15: 1ffff92001696e84
irqentry_exit+0x67/0x70 kernel/entry/common.c:438
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:put_cpu_partial+0x1b0/0x250 mm/slub.c:2742
Code: 3b 44 24 18 0f 85 b4 00 00 00 48 83 c4 20 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 ec aa ac 08 f7 c5 00 02 00 00 74 c0 fb 4d 85 e4 <75> bf eb c8 e8 17 b8 4e 02 85 c0 0f 84 e9 fe ff ff 83 3d a8 b5 ad
RSP: 0018:ffffc9000b4b7598 EFLAGS: 00000246
RAX: c4e772bc0b111600 RBX: ffff888141a5f640 RCX: c4e772bc0b111600
RDX: dffffc0000000000 RSI: ffffffff8acacb60 RDI: ffffffff8b1cf820
RBP: 0000000000000282 R08: ffffffff911e752f R09: 1ffffffff223cea5
R10: dffffc0000000000 R11: fffffbfff223cea6 R12: 0000000000000000
R13: 0000000000000001 R14: ffff888018fcda00 R15: ffff8880b8f44400
__slab_free+0x319/0x400 mm/slub.c:3700
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:767
slab_alloc_node mm/slub.c:3495 [inline]
kmem_cache_alloc_node+0x1af/0x310 mm/slub.c:3540
__alloc_skb+0x103/0x2c0 net/core/skbuff.c:643
alloc_skb include/linux/skbuff.h:1316 [inline]
alloc_skb_with_frags+0xcd/0x7a0 net/core/skbuff.c:6340
sock_alloc_send_pskb+0x883/0x9a0 net/core/sock.c:2830
tun_alloc_skb drivers/net/tun.c:1532 [inline]
tun_get_user+0xa53/0x3d40 drivers/net/tun.c:1853
tun_chr_write_iter+0x119/0x200 drivers/net/tun.c:2055
call_write_iter include/linux/fs.h:2018 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x474/0x9a0 fs/read_write.c:584
ksys_write+0x151/0x260 fs/read_write.c:637
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: 0033:0x7f056259de59
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:00007f0563508028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f0562825fa0 RCX: 00007f056259de59
RDX: 000000000000fdef RSI: 00002000000004c0 RDI: 00000000000000c8
RBP: 00007f0562633e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0562826038 R14: 00007f0562825fa0 R15: 00007fffa689edc8
</TASK>
---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title
If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)
If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report
If you want to undo deduplication, reply with:
#syz undup
syzbot found the following issue on:
HEAD commit: d1cfde2d5d15 Linux 6.6.143
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=15f52c0a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=938110aa66424b94
dashboard link: https://syzkaller.appspot.com/bug?extid=b5fe56e1db1079d6c11e
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/fb0f102e0a80/disk-d1cfde2d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/928fc5f681d8/vmlinux-d1cfde2d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fc3e26207ef8/bzImage-d1cfde2d.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b5fe56...@syzkaller.appspotmail.com
rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 1-....: (10498 ticks this GP) idle=8024/1/0x4000000000000000 softirq=53835/53836 fqs=3107
rcu: hardirqs softirqs csw/system
rcu: number: 906373 0 0
rcu: cputime: 8706 18272 19 ==> 26980(ms)
rcu: (t=10500 jiffies g=63853 q=627 ncpus=2)
CPU: 1 PID: 15098 Comm: syz.3.3241 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:lock_is_held_type+0x13e/0x190 kernel/locking/lockdep.c:5830
Code: 75 40 48 c7 04 24 00 00 00 00 9c 8f 04 24 f7 04 24 00 02 00 00 75 46 41 f7 c5 00 02 00 00 74 01 fb 65 48 8b 04 25 28 00 00 00 <48> 3b 44 24 08 75 3c 89 e8 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f
RSP: 0018:ffffc900001f0328 EFLAGS: 00000206
RAX: c4e772bc0b111600 RBX: ffff888018fcda00 RCX: c4e772bc0b111600
RDX: 0000000000000100 RSI: ffffffff8acadce0 RDI: ffffffff8b1cf820
RBP: 0000000000000000 R08: ffff888018fcda00 R09: 000000000000000b
R10: 000000000000000a R11: 0000000000000100 R12: 0000000000000007
R13: 0000000000000246 R14: ffffffff8e3d5f88 R15: ffff888018fce5f8
FS: 00007f05635086c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000100000000 CR3: 0000000076d31000 CR4: 00000000003506e0
DR0: 0000200000000300 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
<IRQ>
lock_is_held include/linux/lockdep.h:288 [inline]
lockdep_rtnl_is_held+0x1b/0x30 net/core/rtnetlink.c:176
__in6_dev_get include/net/addrconf.h:323 [inline]
ipv6_dev_get_saddr+0x256/0xbb0 net/ipv6/addrconf.c:1866
ip6_route_get_saddr include/net/ip6_route.h:148 [inline]
ip6_dst_lookup_tail+0x107e/0x1660 net/ipv6/ip6_output.c:1138
icmpv6_route_lookup+0xfe/0x600 net/ipv6/icmp.c:363
icmp6_send+0x11b0/0x1b60 net/ipv6/icmp.c:604
__icmpv6_send include/linux/icmpv6.h:28 [inline]
icmpv6_send include/linux/icmpv6.h:49 [inline]
ip6_link_failure+0x3b/0x4c0 net/ipv6/route.c:2839
dst_link_failure include/net/dst.h:437 [inline]
ndisc_error_report+0x112/0x160 net/ipv6/ndisc.c:733
neigh_invalidate+0x23b/0x460 net/core/neighbour.c:1064
neigh_timer_handler+0x911/0xff0 net/core/neighbour.c:1151
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:preempt_schedule_irq+0xba/0x150 kernel/sched/core.c:7010
Code: 00 00 43 c6 44 37 04 f8 74 0b 0f 0b 48 f7 03 08 00 00 00 74 6f bf 01 00 00 00 e8 51 81 c8 f6 e8 8c 6d f9 f6 fb bf 01 00 00 00 <e8> 31 b4 ff ff 43 c6 44 37 08 00 48 c7 44 24 40 00 00 00 00 9c 8f
RSP: 0018:ffffc9000b4b7420 EFLAGS: 00000282
RAX: c4e772bc0b111600 RBX: 0000000000000000 RCX: c4e772bc0b111600
RDX: dffffc0000000000 RSI: ffffffff8acacb60 RDI: 0000000000000001
RBP: ffffc9000b4b74d0 R08: ffffffff911e752f R09: 1ffffffff223cea5
R10: dffffc0000000000 R11: fffffbfff223cea6 R12: 0000000000000000
R13: 0000000000000000 R14: dffffc0000000000 R15: 1ffff92001696e84
irqentry_exit+0x67/0x70 kernel/entry/common.c:438
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:put_cpu_partial+0x1b0/0x250 mm/slub.c:2742
Code: 3b 44 24 18 0f 85 b4 00 00 00 48 83 c4 20 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 ec aa ac 08 f7 c5 00 02 00 00 74 c0 fb 4d 85 e4 <75> bf eb c8 e8 17 b8 4e 02 85 c0 0f 84 e9 fe ff ff 83 3d a8 b5 ad
RSP: 0018:ffffc9000b4b7598 EFLAGS: 00000246
RAX: c4e772bc0b111600 RBX: ffff888141a5f640 RCX: c4e772bc0b111600
RDX: dffffc0000000000 RSI: ffffffff8acacb60 RDI: ffffffff8b1cf820
RBP: 0000000000000282 R08: ffffffff911e752f R09: 1ffffffff223cea5
R10: dffffc0000000000 R11: fffffbfff223cea6 R12: 0000000000000000
R13: 0000000000000001 R14: ffff888018fcda00 R15: ffff8880b8f44400
__slab_free+0x319/0x400 mm/slub.c:3700
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:767
slab_alloc_node mm/slub.c:3495 [inline]
kmem_cache_alloc_node+0x1af/0x310 mm/slub.c:3540
__alloc_skb+0x103/0x2c0 net/core/skbuff.c:643
alloc_skb include/linux/skbuff.h:1316 [inline]
alloc_skb_with_frags+0xcd/0x7a0 net/core/skbuff.c:6340
sock_alloc_send_pskb+0x883/0x9a0 net/core/sock.c:2830
tun_alloc_skb drivers/net/tun.c:1532 [inline]
tun_get_user+0xa53/0x3d40 drivers/net/tun.c:1853
tun_chr_write_iter+0x119/0x200 drivers/net/tun.c:2055
call_write_iter include/linux/fs.h:2018 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x474/0x9a0 fs/read_write.c:584
ksys_write+0x151/0x260 fs/read_write.c:637
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: 0033:0x7f056259de59
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:00007f0563508028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f0562825fa0 RCX: 00007f056259de59
RDX: 000000000000fdef RSI: 00002000000004c0 RDI: 00000000000000c8
RBP: 00007f0562633e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0562826038 R14: 00007f0562825fa0 R15: 00007fffa689edc8
</TASK>
---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title
If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)
If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report
If you want to undo deduplication, reply with:
#syz undup
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