Re: [PATCH 6.12 28/70] mptcp: fix soft lockup in mptcp_recvmsg()

[Li Xiasong <lixiasong1@huawei.com>]

Hi,

One clarification to my previous email:

The `v6.18.32` kernel used in my test was built with commit
`58b58b9ba89c` ("mptcp: fix soft lockup in mptcp_recvmsg()") reverted.
So the reproduction result I reported for `v6.18.32` is based on a
kernel without that patch.

Regards,
Li Xiasong

On 5/27/2026 6:22 PM, Li Xiasong wrote:
> Hi, Jiping
> 
> On 5/27/2026 11:05 AM, Jiping Ma wrote:
>> Hi, Xiasong
>>
>> Could you share how to reproduce the issue?
>> I used the following code to reproduce it, and do the test in v6.18.32. but the test results are the same with and without the fix(I revert the commit 58b58b9ba89c43914eea90c18928e51852d10c24).
>> The client task will be waked up after 10 minutes.  There is not soft lockup.
>>
> 
> Thanks for sharing the reproducer.
> 
> Your test program itself looks fine to me, and I can reproduce the issue
> with the reproducer you provided in my test environment.[0]
> 
> I think the reproduction result depends on the kernel preemption model.
> The issue is easier to trigger with a non-preemptible kernel
> (e.g. `PREEMPT_NONE`). On other preemption configurations, it may be
> harder to reproduce, but the program can still be observed consuming
> nearly 100% system CPU. So the same test can show different behavior
> under different `CONFIG_PREEMPT*` settings.
> 
> Also, if you want to reproduce this on `6.6.y` or `6.12.y`, based on
> the previous analysis, have the sender transmit two packets with an
> interval between them.
> 
> Hope this helps.
> 
> [0] Relevant dmesg log:
> Linux ubuntu 6.18.32+ #15 SMP PREEMPT_DYNAMIC Wed May 27 15:25:52 CST 2026 x86_64 x86_64 x86_64 GNU/Linux
> root@ubuntu:~# [  960.743413] watchdog: BUG: soft lockup - CPU#5 stuck for 261s! [client:1260]
> [  960.743433] Modules linked in:
> [  960.743463] CPU: 5 UID: 0 PID: 1260 Comm: client Not tainted 6.18.32+ #15 PREEMPT(none)
> [  960.743469] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> [  960.743474] RIP: 0010:_raw_spin_lock_bh+0x1b/0x60
> [  960.743518] Code: 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 65 81 05 d0 a2 a1 01 01 02 00 00 31 c0 ba 01 00 00 00 f0 0f b1 17 <75> 1b 31 c0 31 d2 31 c9 31 f6 31 ff 45 31 c0 45 31 c9 45 31 d2 45
> [  960.743521] RSP: 0018:ffffc9000259fb08 EFLAGS: 00000246
> [  960.743524] RAX: 0000000000000000 RBX: ffff888106efc480 RCX: 0000000000000000
> [  960.743529] RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffff888106efc5c0
> [  960.743531] RBP: ffffc9000259fb68 R08: 0000000000000000 R09: 0000000000000000
> [  960.743533] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> [  960.743535] R13: ffff888106efc5c0 R14: ffff888106efc528 R15: 0000000000000000
> [  960.743537] FS:  000079482a7b7740(0000) GS:ffff8881b70e7000(0000) knlGS:0000000000000000
> [  960.743540] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  960.743542] CR2: 00005a8d794c3008 CR3: 00000001033ea000 CR4: 00000000000006f0
> [  960.743547] Call Trace:
> [  960.743550]  <TASK>
> [  960.743552]  ? sk_wait_data+0xc2/0x1a0
> [  960.743564]  ? __pfx_woken_wake_function+0x10/0x10
> [  960.743571]  mptcp_recvmsg+0x623/0x9a0
> [  960.743578]  ? __wake_up+0x45/0x70
> [  960.743582]  inet_recvmsg+0x124/0x130
> [  960.743588]  ? apparmor_socket_recvmsg+0x25/0x40
> [  960.743595]  ? security_socket_recvmsg+0x1a9/0x1d0
> [  960.743602]  sock_recvmsg+0xb7/0xc0
> [  960.743608]  __sys_recvfrom+0xd2/0x170
> [  960.743612]  ? ksys_write+0x69/0xf0
> [  960.743618]  ? __x64_sys_write+0x19/0x30
> [  960.743622]  ? x64_sys_call+0x18fc/0x2760
> [  960.743628]  ? do_syscall_64+0xb8/0x1300
> [  960.743635]  ? do_syscall_64+0xb8/0x1300
> [  960.743640]  __x64_sys_recvfrom+0x24/0x40
> [  960.743642]  x64_sys_call+0x2694/0x2760
> [  960.743646]  do_syscall_64+0x80/0x1300
> [  960.743650]  ? count_memcg_events+0xed/0x1e0
> [  960.743655]  ? handle_mm_fault+0x210/0x2f0
> [  960.743661]  ? do_user_addr_fault+0x300/0x8d0
> [  960.743666]  ? irqentry_exit_to_user_mode+0x2e/0x330
> [  960.743670]  ? irqentry_exit+0x43/0x50
> [  960.743672]  ? exc_page_fault+0x93/0x1b0
> [  960.743675]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
> [  960.743678] RIP: 0033:0x79482a49eba6
> [  960.743691] Code: 00 00 48 8b 15 53 12 17 00 64 89 02 48 c7 c2 ff ff ff ff 48 8b 5d f8 c9 48 89 d0 c3 0f 1f 84 00 00 00 00 00 48 8b 45 10 0f 05 <48> 63 d0 3d 00 f0 ff ff 77 10 48 8b 5d f8 48 89 d0 c9 c3 0f 1f 80
> [  960.743693] RSP: 002b:00007ffd26c7bdc0 EFLAGS: 00000202 ORIG_RAX: 000000000000002d
> [  960.743696] RAX: ffffffffffffffda RBX: 000079482a7b7740 RCX: 000079482a49eba6
> [  960.743698] RDX: 0000000000000400 RSI: 00007ffd26c7be20 RDI: 0000000000000003
> [  960.743699] RBP: 00007ffd26c7bdd0 R08: 0000000000000000 R09: 0000000000000000
> [  960.743701] R10: 0000000000000102 R11: 0000000000000202 R12: 0000000000000001
> [  960.743702] R13: 0000000000000000 R14: 00005a8d75ae6d78 R15: 000079482a806000
> [  960.743707]  </TASK>