Hi,

I observed system hangs when using OpenVPN across suspend/resume
under heavy network load.

The issue can be reproduced with:
1. Establish an OpenVPN connection
2. Generate traffic with iperf3
3. Add CPU/memory pressure with stress-ng
4. Suspend and resume the system

After resume, the system may become unresponsive. SysRq output shows
tasks spinning on sk->sk_lock.slock, and RCU stall warnings are
observed.

Kernel logs and stack traces:
kernel: watchdog: BUG: soft lockup - CPU#4 stuck for 22s! [stress-ng-cpu:11506]
kernel: CPU#4 Utilization every 4000ms during lockup:
kernel:         #1:   0% system,        100% softirq,          1% hardirq,          0% idle
kernel:         #2:   0% system,        100% softirq,          0% hardirq,          0% idle
kernel:         #3:   0% system,        100% softirq,          1% hardirq,          0% idle
kernel:         #4:   0% system,        100% softirq,          0% hardirq,          0% idle
kernel:         #5:   0% system,        100% softirq,          0% hardirq,          0% idle
kernel: CPU: 4 UID: 1000 PID: 11506 Comm: stress-ng-cpu Tainted: G     U              7.0.2-2-cachyos #1 PREEMPT  136cb9373f01c1def72b1b5def9dd1fcc7884035
kernel: Tainted: [U]=USER
kernel: Hardware name: Framework Laptop 13 (AMD Ryzen 7040Series)/FRANMDCP05, BIOS 03.18 01/08/2026
kernel: RIP: 0010:native_queued_spin_lock_slowpath+0x5a/0x260
kernel: Code: 08 0f 92 c0 b9 ff 00 ff ff 23 0f 89 c2 c1 e2 08 09 ca 81 fa 00 01 00 00 73 5a 85 c9 74 0e 66 90 80 3f 00 74 07 f3 90 80 3f 00 <75> f9 66 c7 07 01 00 65 48 ff 05 3f c6 d8 01 5b 41 5e 41 5f 5d e9
kernel: RSP: 0000:ffffcf548d9bb758 EFLAGS: 00000202
kernel: RAX: 0000000000000000 RBX: ffff8ec75f9f4d48 RCX: 0000000000000001
kernel: RDX: 0000000000000001 RSI: 0000000000000001 RDI: ffff8ec75f9f4d48
kernel: RBP: 0000000000000000 R08: 0000000000000000 R09: ffff8ec8547abd80
kernel: R10: 0000000000000020 R11: 0000000000000020 R12: ffff8ec75f9f4c00
kernel: R13: ffff8ec862d9d400 R14: ffff8ec753ade400 R15: ffff8ec771548800
kernel: FS:  00007f9b4fcd0b00(0000) GS:ffff8eccfe99c000(0000) knlGS:0000000000000000
kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
kernel: CR2: 00007ffb7e1f8e38 CR3: 0000000166ced000 CR4: 0000000000f50ef0
kernel: PKRU: 55555554
kernel: Call Trace:
kernel:  <TASK>
kernel:  _raw_spin_lock+0x2a/0x40
kernel:  ovpn_tcp_send_skb+0x4c/0x130 [ovpn 03847a96bef64ed5cc535ef1935e53bb388bcced]
kernel:  ovpn_encrypt_post+0x95/0x1f0 [ovpn 03847a96bef64ed5cc535ef1935e53bb388bcced]
kernel:  ovpn_send+0x15f/0x230 [ovpn 03847a96bef64ed5cc535ef1935e53bb388bcced]
kernel:  ovpn_net_xmit+0x30f/0x560 [ovpn 03847a96bef64ed5cc535ef1935e53bb388bcced]
kernel:  dev_hard_start_xmit+0x93/0x140
kernel:  __dev_queue_xmit+0x99b/0xa80
kernel:  ? __dev_queue_xmit+0x6f/0xa80
kernel:  ? srso_alias_return_thunk+0x5/0xfbef5
kernel:  ? nf_hook_slow+0x4b/0xd0
kernel:  ? __pfx_ip_finish_output+0x10/0x10
kernel:  ? srso_alias_return_thunk+0x5/0xfbef5
kernel:  ? nf_hook+0x9c/0xb0
kernel:  ip_finish_output2+0x189/0x320
kernel:  dst_output+0x99/0xd0
kernel:  __ip_queue_xmit+0x209/0x350
kernel:  __tcp_transmit_skb+0x4cb/0xba0
kernel:  ? srso_alias_return_thunk+0x5/0xfbef5
kernel:  ? __alloc_skb+0x2b6/0x340
kernel:  ? srso_alias_return_thunk+0x5/0xfbef5
kernel:  ? skb_split+0x5f/0x3c0
kernel:  tcp_write_xmit+0xad3/0x1a50
kernel:  ? __pfx_tcp_write_timer+0x10/0x10
kernel:  tcp_send_loss_probe+0x94/0x2b0
kernel:  ? __pfx_tcp_write_timer+0x10/0x10
kernel:  tcp_write_timer+0x67/0xb0
kernel:  __run_timer_base+0x33d/0x500
kernel:  tmigr_handle_remote+0x3da/0x3e0
kernel:  run_timer_softirq.cold+0x47/0x394
kernel:  ? srso_alias_return_thunk+0x5/0xfbef5
kernel:  ? __pfx_tick_nohz_handler+0x10/0x10
kernel:  ? srso_alias_return_thunk+0x5/0xfbef5
kernel:  ? ktime_get+0x48/0xa0
kernel:  ? srso_alias_return_thunk+0x5/0xfbef5
kernel:  ? clockevents_program_event+0xaa/0xf0
kernel:  ? srso_alias_return_thunk+0x5/0xfbef5
kernel:  ? srso_alias_return_thunk+0x5/0xfbef5
kernel:  irq_exit_rcu+0x1ad/0x290
kernel:  sysvec_apic_timer_interrupt+0x33/0x80
kernel:  asm_sysvec_apic_timer_interrupt+0x1a/0x20
kernel: RIP: 0033:0x559fc1ece66f
kernel: Code: 44 89 c8 c0 e8 03 44 31 c0 83 e0 01 66 41 d1 e8 f7 d8 66 25 08 84 44 31 c0 45 89 c8 41 c0 e8 04 41 31 c0 41 83 e0 01 41 f7 d8 <66> 41 81 e0 08 84 66 d1 e8 41 31 c0 44 89 c8 c0 e8 05 44 31 c0 83
kernel: RSP: 002b:00007ffe1344e860 EFLAGS: 00000297
kernel: RAX: 00000000ffff5912 RBX: 000000000000000a RCX: 00007ffe1344ebcb
kernel: RDX: 00007ffe1344ea27 RSI: 00007ffe1344ec60 RDI: 0000559fc318d450
kernel: RBP: 00007ffe1344edf0 R08: 00000000ffffffff R09: 00000000000000b4
kernel: R10: 0000559fc333b3e0 R11: 0000000000000000 R12: 00007f9b4fcc6258
kernel: R13: 0000000000000000 R14: 0000559fc316ed00 R15: 0000559fc3337e00
kernel:  </TASK>


Dao Zhong Ma (1):
  ovpn: tcp - defer TX from softirq to workqueue to avoid RCU stalls

 drivers/net/ovpn/tcp.c | 80 +++++++++++++++++++++++++++++++-----------
 1 file changed, 59 insertions(+), 21 deletions(-)

--
2.54.0