linux-kernel - Re: [PATCH v4 0/4] reparent the THP split queue

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Message-ID: <4a134193-ee55-434c-98a9-ca3052bab11b@linux.dev>
Date: Sat, 11 Oct 2025 08:51:21 +0800
From: Qi Zheng <qi.zheng@...ux.dev>
To: Zi Yan <ziy@...dia.com>, akpm@...ux-foundation.org
Cc: hannes@...xchg.org, hughd@...gle.com, mhocko@...e.com,
 roman.gushchin@...ux.dev, shakeel.butt@...ux.dev, muchun.song@...ux.dev,
 david@...hat.com, lorenzo.stoakes@...cle.com, harry.yoo@...cle.com,
 baolin.wang@...ux.alibaba.com, Liam.Howlett@...cle.com, npache@...hat.com,
 ryan.roberts@....com, dev.jain@....com, baohua@...nel.org,
 lance.yang@...ux.dev, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 cgroups@...r.kernel.org, Qi Zheng <zhengqi.arch@...edance.com>
Subject: Re: [PATCH v4 0/4] reparent the THP split queue

Hi Zi,

On 10/11/25 12:25 AM, Zi Yan wrote:
> On 3 Oct 2025, at 12:53, Qi Zheng wrote:
> 

[snip]

>>
> 
> Hi Qi,
> 
> I got CPU soft locks when run "echo 3 | sudo tee /proc/sys/vm/drop_caches"
> with today's mm-new on a freshly booted system. Reverting Patch 3 (and Patch 4)
> of your patchset solves the issue.
> 
> My config file is attached. My kernel relevant kernel parameters are:
> "cgroup_no_v1=all transparent_hugepage=always thp_shmem=2M:always".
> The machine is a 8GB 8-core x86_64 VM.

Thanks for your report. I'm on vacation and will be back in two days,
I'll try to reproduce it locally and fix it.

And hi Andrew, please help drop this patch set from mm-new first.

Thanks,
Qi

> 
> The kernel log:
> 
> [   36.441539] watchdog: BUG: soft lockup - CPU#0 stuck for 26s! [tee:810]
> [   36.441549] Modules linked in:
> [   36.441566] CPU: 0 UID: 0 PID: 810 Comm: tee Not tainted 6.17.0-mm-everything-2024-01-29-07-19-no-mglru+ #526 PREEMPT(voluntary)
> [   36.441570] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
> [   36.441574] RIP: 0010:_raw_spin_unlock_irqrestore+0x19/0x40
> [   36.441592] Code: 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 53 48 89 f3 e8 92 68 fd fe 80 e7 02 74 06 fb 0f 1f 44 00 00 <65> ff 0d d0 5f 7e 01 74 06 5b c3 cc cc cc cc 0f 1f 44 00 00 5b c3
> [   36.441594] RSP: 0018:ffffc900029afb60 EFLAGS: 00000202
> [   36.441598] RAX: 0000000000000001 RBX: 0000000000000286 RCX: ffff888101168670
> [   36.441601] RDX: 0000000000000001 RSI: 0000000000000286 RDI: ffff888101168658
> [   36.441602] RBP: 0000000000000001 R08: ffff88813ba44ec0 R09: 0000000000000000
> [   36.441603] R10: 00000000000001a8 R11: 0000000000000000 R12: ffff8881011685e0
> [   36.441604] R13: 0000000000000000 R14: ffff888101168000 R15: ffffc900029afd60
> [   36.441606] FS:  00007f7fe3655740(0000) GS:ffff8881b7e5d000(0000) knlGS:0000000000000000
> [   36.441607] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   36.441608] CR2: 0000563d4d439bf0 CR3: 000000010873c006 CR4: 0000000000370ef0
> [   36.441614] Call Trace:
> [   36.441616]  <TASK>
> [   36.441619]  deferred_split_scan+0x1e0/0x480
> [   36.441627]  ? _raw_spin_unlock_irqrestore+0xe/0x40
> [   36.441630]  ? kvfree_rcu_queue_batch+0x96/0x1c0
> [   36.441634]  ? do_raw_spin_unlock+0x46/0xd0
> [   36.441639]  ? kfree_rcu_monitor+0x1da/0x2c0
> [   36.441641]  ? list_lru_count_one+0x47/0x90
> [   36.441644]  do_shrink_slab+0x153/0x360
> [   36.441649]  shrink_slab+0xd3/0x390
> [   36.441652]  drop_slab+0x7d/0x130
> [   36.441655]  drop_caches_sysctl_handler+0x98/0xb0
> [   36.441660]  proc_sys_call_handler+0x1c7/0x2c0
> [   36.441664]  vfs_write+0x221/0x450
> [   36.441669]  ksys_write+0x6c/0xe0
> [   36.441672]  do_syscall_64+0x50/0x200
> [   36.441675]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
> [   36.441678] RIP: 0033:0x7f7fe36e7687
> [   36.441685] Code: 48 89 fa 4c 89 df e8 58 b3 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
> [   36.441686] RSP: 002b:00007ffdffcbba10 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
> [   36.441688] RAX: ffffffffffffffda RBX: 00007f7fe3655740 RCX: 00007f7fe36e7687
> [   36.441689] RDX: 0000000000000002 RSI: 00007ffdffcbbbb0 RDI: 0000000000000003
> [   36.441690] RBP: 00007ffdffcbbbb0 R08: 0000000000000000 R09: 0000000000000000
> [   36.441691] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000002
> [   36.441692] R13: 0000558d40be64c0 R14: 00007f7fe383de80 R15: 0000000000000002
> [   36.441694]  </TASK>
> [   64.441531] watchdog: BUG: soft lockup - CPU#0 stuck for 53s! [tee:810]
> [   64.441537] Modules linked in:
> [   64.441545] CPU: 0 UID: 0 PID: 810 Comm: tee Tainted: G             L      6.17.0-mm-everything-2024-01-29-07-19-no-mglru+ #526 PREEMPT(voluntary)
> [   64.441548] Tainted: [L]=SOFTLOCKUP
> [   64.441552] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
> [   64.441555] RIP: 0010:_raw_spin_unlock_irqrestore+0x19/0x40
> [   64.441565] Code: 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 53 48 89 f3 e8 92 68 fd fe 80 e7 02 74 06 fb 0f 1f 44 00 00 <65> ff 0d d0 5f 7e 01 74 06 5b c3 cc cc cc cc 0f 1f 44 00 00 5b c3
> [   64.441566] RSP: 0018:ffffc900029afb60 EFLAGS: 00000202
> [   64.441568] RAX: 0000000000000001 RBX: 0000000000000286 RCX: ffff888101168670
> [   64.441570] RDX: 0000000000000001 RSI: 0000000000000286 RDI: ffff888101168658
> [   64.441571] RBP: 0000000000000001 R08: ffff88813ba44ec0 R09: 0000000000000000
> [   64.441572] R10: 00000000000001a8 R11: 0000000000000000 R12: ffff8881011685e0
> [   64.441573] R13: 0000000000000000 R14: ffff888101168000 R15: ffffc900029afd60
> [   64.441574] FS:  00007f7fe3655740(0000) GS:ffff8881b7e5d000(0000) knlGS:0000000000000000
> [   64.441576] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   64.441577] CR2: 0000563d4d439bf0 CR3: 000000010873c006 CR4: 0000000000370ef0
> [   64.441581] Call Trace:
> [   64.441583]  <TASK>
> [   64.441591]  deferred_split_scan+0x1e0/0x480
> [   64.441598]  ? _raw_spin_unlock_irqrestore+0xe/0x40
> [   64.441599]  ? kvfree_rcu_queue_batch+0x96/0x1c0
> [   64.441603]  ? do_raw_spin_unlock+0x46/0xd0
> [   64.441607]  ? kfree_rcu_monitor+0x1da/0x2c0
> [   64.441610]  ? list_lru_count_one+0x47/0x90
> [   64.441613]  do_shrink_slab+0x153/0x360
> [   64.441618]  shrink_slab+0xd3/0x390
> [   64.441621]  drop_slab+0x7d/0x130
> [   64.441624]  drop_caches_sysctl_handler+0x98/0xb0
> [   64.441629]  proc_sys_call_handler+0x1c7/0x2c0
> [   64.441632]  vfs_write+0x221/0x450
> [   64.441638]  ksys_write+0x6c/0xe0
> [   64.441641]  do_syscall_64+0x50/0x200
> [   64.441645]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
> [   64.441648] RIP: 0033:0x7f7fe36e7687
> [   64.441654] Code: 48 89 fa 4c 89 df e8 58 b3 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
> [   64.441656] RSP: 002b:00007ffdffcbba10 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
> [   64.441658] RAX: ffffffffffffffda RBX: 00007f7fe3655740 RCX: 00007f7fe36e7687
> [   64.441659] RDX: 0000000000000002 RSI: 00007ffdffcbbbb0 RDI: 0000000000000003
> [   64.441660] RBP: 00007ffdffcbbbb0 R08: 0000000000000000 R09: 0000000000000000
> [   64.441661] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000002
> [   64.441662] R13: 0000558d40be64c0 R14: 00007f7fe383de80 R15: 0000000000000002
> [   64.441663]  </TASK>
> 
> 
> 
> --
> Best Regards,
> Yan, Zi