[v6.1] INFO: rcu detected stall in tcp_write_timer (2)

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Mar 5, 2026, 10:16:22 PM (2 days ago) Mar 5
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Hello,

syzbot found the following issue on:

HEAD commit: f2ddafa93a25 Linux 6.1.166
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=17a8fb5a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0605c5af04d7603
dashboard link: https://syzkaller.appspot.com/bug?extid=8e8fec64822c9c0eb31a
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9f94eb2783d1/disk-f2ddafa9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b8cfb93aeed4/vmlinux-f2ddafa9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d2dd53c6d41c/bzImage-f2ddafa9.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8e8fec...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 0-.... } 2654 jiffies s: 25937 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: 13438 Comm: syz.4.3173 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:__irq_exit_rcu+0x0/0x230 kernel/softirq.c:670
Code: 16 ff ff ff 66 0f 1f 44 00 00 e8 1b 00 00 00 48 c7 c7 40 08 8b 8a e8 5f a9 dd 08 65 ff 0d 8c 04 b3 7e c3 0f 1f 80 00 00 00 00 <55> 48 89 e5 41 57 41 56 41 55 41 54 53 48 83 e4 e0 48 83 ec 60 65
RSP: 0018:ffffc90000006f30 EFLAGS: 00000086
RAX: 0000000000000000 RBX: ffffc90000006f58 RCX: e4110b4135399600
RDX: 0000000000000000 RSI: ffffffff8a88f1c0 RDI: ffffffff8adf0f60
RBP: 0000000000000000 R08: ffffffff8e1fd76f R09: 1ffffffff1c3faed
R10: dffffc0000000000 R11: fffffbfff1c3faee R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS: 00007f6b9e7916c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd0a51e9e80 CR3: 0000000060597000 CR4: 00000000003506f0
DR0: 0000200000000300 DR1: 0000200000000300 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
<IRQ>
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+0x52/0xc0 arch/x86/kernel/apic/apic.c:1118
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:rcu_dynticks_curr_cpu_in_eqs include/linux/context_tracking.h:122 [inline]
RIP: 0010:rcu_is_watching+0x36/0xa0 kernel/rcu/tree.c:721
Code: e8 4f aa c0 08 89 c3 83 f8 08 73 60 49 bf 00 00 00 00 00 fc ff df 4c 8d 34 dd 80 09 65 8c 4c 89 f0 48 c1 e8 03 42 80 3c 38 00 <74> 08 4c 89 f7 e8 b0 ed 66 00 48 c7 c3 08 58 03 00 49 03 1e 48 89
RSP: 0018:ffffc90000007000 EFLAGS: 00000246
RAX: 1ffffffff18ca130 RBX: 0000000000000000 RCX: e4110b4135399600
RDX: 0000000000000000 RSI: ffffffff8adf0f40 RDI: ffffffff8adf0f00
RBP: ffffc90000007128 R08: ffffffff8e1fd76f R09: 1ffffffff1c3faed
R10: dffffc0000000000 R11: fffffbfff1c3faee R12: 0000000000000000
R13: 1ffff92000000e10 R14: ffffffff8c650980 R15: dffffc0000000000
trace_lock_acquire include/trace/events/lock.h:24 [inline]
lock_acquire+0xe3/0x4a0 kernel/locking/lockdep.c:5633
rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
rcu_read_lock include/linux/rcupdate.h:791 [inline]
trace_call_bpf+0xe0/0x6b0 kernel/trace/bpf_trace.c:134
perf_trace_run_bpf_submit+0x79/0x1c0 kernel/events/core.c:9997
perf_trace_lock_acquire+0x33f/0x3e0 include/trace/events/lock.h:24
trace_lock_acquire include/trace/events/lock.h:24 [inline]
lock_acquire+0x452/0x4a0 kernel/locking/lockdep.c:5633
rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
rcu_read_lock include/linux/rcupdate.h:791 [inline]
is_bpf_text_address+0x43/0x2a0 kernel/bpf/core.c:735
kernel_text_address+0x9c/0xd0 kernel/extable.c:125
__kernel_text_address+0x9/0x30 kernel/extable.c:79
unwind_get_return_address+0x49/0x80 arch/x86/kernel/unwind_orc.c:323
arch_stack_walk+0xf2/0x140 arch/x86/kernel/stacktrace.c:26
stack_trace_save+0xa6/0xf0 kernel/stacktrace.c:122
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
kasan_save_free_info+0x2d/0x50 mm/kasan/generic.c:516
____kasan_slab_free+0x126/0x1e0 mm/kasan/common.c:237
kasan_slab_free include/linux/kasan.h:177 [inline]
slab_free_hook mm/slub.c:1729 [inline]
slab_free_freelist_hook+0x131/0x1a0 mm/slub.c:1755
slab_free mm/slub.c:3687 [inline]
__kmem_cache_free+0xb6/0x1f0 mm/slub.c:3700
skb_free_head net/core/skbuff.c:762 [inline]
skb_release_data+0x5db/0x7c0 net/core/skbuff.c:791
skb_release_all net/core/skbuff.c:856 [inline]
__kfree_skb+0x4c/0x60 net/core/skbuff.c:870
tcp_write_queue_purge+0x13f/0x2f0 net/ipv4/tcp.c:3122
tcp_done_with_error+0x3f/0xc0 net/ipv4/tcp_input.c:4408
tcp_write_err net/ipv4/tcp_timer.c:70 [inline]
tcp_probe_timer net/ipv4/tcp_timer.c:396 [inline]
tcp_write_timer_handler+0x655/0x900 net/ipv4/tcp_timer.c:663
tcp_write_timer+0x126/0x280 net/ipv4/tcp_timer.c:676
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:preempt_schedule_irq+0xb6/0x160 kernel/sched/core.c:6874
Code: 00 00 43 c6 44 37 04 f8 74 0b 0f 0b 48 f7 03 08 00 00 00 74 7f bf 01 00 00 00 e8 f5 42 23 f7 e8 b0 35 53 f7 fb bf 01 00 00 00 <e8> 75 b9 ff ff 43 c6 44 37 08 00 48 c7 44 24 40 00 00 00 00 9c 8f
RSP: 0018:ffffc900049bf2c0 EFLAGS: 00000282
RAX: e4110b4135399600 RBX: 0000000000000000 RCX: e4110b4135399600
RDX: dffffc0000000000 RSI: ffffffff8a8c1220 RDI: 0000000000000001
RBP: ffffc900049bf370 R08: ffffffff90af624f R09: 1ffffffff215ec49
R10: dffffc0000000000 R11: fffffbfff215ec4a R12: 0000000000000000
R13: 0000000000000000 R14: dffffc0000000000 R15: 1ffff92000937e58
irqentry_exit+0x63/0x70 kernel/entry/common.c:439
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:put_cpu_partial+0x1b0/0x250 mm/slub.c:2666
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 7c 21 5a 08 f7 c5 00 02 00 00 74 c0 fb 4d 85 e4 <75> bf eb c8 e8 67 fd 3a 02 85 c0 0f 84 e9 fe ff ff 83 3d 00 28 4d
RSP: 0018:ffffc900049bf438 EFLAGS: 00000246
RAX: e4110b4135399600 RBX: ffff888017441b40 RCX: e4110b4135399600
RDX: dffffc0000000000 RSI: ffffffff8a8c1220 RDI: ffffffff8adf0f60
RBP: 0000000000000282 R08: ffffffff90af624f R09: 1ffffffff215ec49
R10: dffffc0000000000 R11: fffffbfff215ec4a R12: 0000000000000000
R13: 0000000000000000 R14: ffff88802e76d940 R15: ffff8880b8e3e740
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/0x480 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+0x123/0x2f0 mm/slub.c:3383
kmem_cache_zalloc include/linux/slab.h:689 [inline]
__kernfs_new_node+0xe1/0x810 fs/kernfs/dir.c:614
kernfs_new_node+0x148/0x250 fs/kernfs/dir.c:690
__kernfs_create_file+0x47/0x2e0 fs/kernfs/file.c:1068
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
create_dir lib/kobject.c:68 [inline]
kobject_add_internal+0x663/0xcc0 lib/kobject.c:231
kobject_add_varg lib/kobject.c:366 [inline]
kobject_init_and_add+0x128/0x190 lib/kobject.c:449
netdev_queue_add_kobject net/core/net-sysfs.c:1664 [inline]
netdev_queue_update_kobjects+0x200/0x480 net/core/net-sysfs.c:1716
register_queue_kobjects net/core/net-sysfs.c:1777 [inline]
netdev_register_kobject+0x273/0x320 net/core/net-sysfs.c:2017
register_netdevice+0x12dc/0x1b00 net/core/dev.c:10230
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: 0033:0x7f6b9d99c799
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:00007f6b9e791028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f6b9dc16090 RCX: 00007f6b9d99c799
RDX: 0000200000000000 RSI: 00000000400454ca RDI: 0000000000000008
RBP: 00007f6b9da32bd9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6b9dc16128 R14: 00007f6b9dc16090 R15: 00007ffd5eb41d18
</TASK>


---
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