linux-kernel - Re: [PATCH v1 2/2] mm/slab/kvfree_rcu: Switch to WQ_MEM

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <14620f80-33e1-4755-8178-5dc7e860689e@nvidia.com>
Date: Thu, 6 Mar 2025 13:26:37 -0500
From: Joel Fernandes <joelagnelf@...dia.com>
To: paulmck@...nel.org
Cc: "Uladzislau Rezki (Sony)" <urezki@...il.com>, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>, Vlastimil Babka <vbabka@...e.cz>,
 RCU <rcu@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
 Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>,
 David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Hyeonggon Yoo <42.hyeyoo@...il.com>,
 Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>, stable@...r.kernel.org,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Keith Busch <kbusch@...nel.org>
Subject: Re: [PATCH v1 2/2] mm/slab/kvfree_rcu: Switch to WQ_MEM_RECLAIM wq



On 3/4/2025 9:55 AM, Paul E. McKenney wrote:
> On Mon, Mar 03, 2025 at 11:08:24AM -0500, Joel Fernandes wrote:
>> On Fri, Feb 28, 2025 at 01:13:56PM +0100, Uladzislau Rezki (Sony) wrote:
>>> Currently kvfree_rcu() APIs use a system workqueue which is
>>> "system_unbound_wq" to driver RCU machinery to reclaim a memory.
>>>
>>> Recently, it has been noted that the following kernel warning can
>>> be observed:
>>>
>>> <snip>
>>> workqueue: WQ_MEM_RECLAIM nvme-wq:nvme_scan_work is flushing !WQ_MEM_RECLAIM events_unbound:kfree_rcu_work
>>>   WARNING: CPU: 21 PID: 330 at kernel/workqueue.c:3719 check_flush_dependency+0x112/0x120
>>>   Modules linked in: intel_uncore_frequency(E) intel_uncore_frequency_common(E) skx_edac(E) ...
>>>   CPU: 21 UID: 0 PID: 330 Comm: kworker/u144:6 Tainted: G            E      6.13.2-0_g925d379822da #1
>>>   Hardware name: Wiwynn Twin Lakes MP/Twin Lakes Passive MP, BIOS YMM20 02/01/2023
>>>   Workqueue: nvme-wq nvme_scan_work
>>>   RIP: 0010:check_flush_dependency+0x112/0x120
>>>   Code: 05 9a 40 14 02 01 48 81 c6 c0 00 00 00 48 8b 50 18 48 81 c7 c0 00 00 00 48 89 f9 48 ...
>>>   RSP: 0018:ffffc90000df7bd8 EFLAGS: 00010082
>>>   RAX: 000000000000006a RBX: ffffffff81622390 RCX: 0000000000000027
>>>   RDX: 00000000fffeffff RSI: 000000000057ffa8 RDI: ffff88907f960c88
>>>   RBP: 0000000000000000 R08: ffffffff83068e50 R09: 000000000002fffd
>>>   R10: 0000000000000004 R11: 0000000000000000 R12: ffff8881001a4400
>>>   R13: 0000000000000000 R14: ffff88907f420fb8 R15: 0000000000000000
>>>   FS:  0000000000000000(0000) GS:ffff88907f940000(0000) knlGS:0000000000000000
>>>   CR2: 00007f60c3001000 CR3: 000000107d010005 CR4: 00000000007726f0
>>>   PKRU: 55555554
>>>   Call Trace:
>>>    <TASK>
>>>    ? __warn+0xa4/0x140
>>>    ? check_flush_dependency+0x112/0x120
>>>    ? report_bug+0xe1/0x140
>>>    ? check_flush_dependency+0x112/0x120
>>>    ? handle_bug+0x5e/0x90
>>>    ? exc_invalid_op+0x16/0x40
>>>    ? asm_exc_invalid_op+0x16/0x20
>>>    ? timer_recalc_next_expiry+0x190/0x190
>>>    ? check_flush_dependency+0x112/0x120
>>>    ? check_flush_dependency+0x112/0x120
>>>    __flush_work.llvm.1643880146586177030+0x174/0x2c0
>>>    flush_rcu_work+0x28/0x30
>>>    kvfree_rcu_barrier+0x12f/0x160
>>>    kmem_cache_destroy+0x18/0x120
>>>    bioset_exit+0x10c/0x150
>>>    disk_release.llvm.6740012984264378178+0x61/0xd0
>>>    device_release+0x4f/0x90
>>>    kobject_put+0x95/0x180
>>>    nvme_put_ns+0x23/0xc0
>>>    nvme_remove_invalid_namespaces+0xb3/0xd0
>>>    nvme_scan_work+0x342/0x490
>>>    process_scheduled_works+0x1a2/0x370
>>>    worker_thread+0x2ff/0x390
>>>    ? pwq_release_workfn+0x1e0/0x1e0
>>>    kthread+0xb1/0xe0
>>>    ? __kthread_parkme+0x70/0x70
>>>    ret_from_fork+0x30/0x40
>>>    ? __kthread_parkme+0x70/0x70
>>>    ret_from_fork_asm+0x11/0x20
>>>    </TASK>
>>>   ---[ end trace 0000000000000000 ]---
>>> <snip>
>>>
>>> To address this switch to use of independent WQ_MEM_RECLAIM
>>> workqueue, so the rules are not violated from workqueue framework
>>> point of view.
>>>
>>> Apart of that, since kvfree_rcu() does reclaim memory it is worth
>>> to go with WQ_MEM_RECLAIM type of wq because it is designed for
>>> this purpose.
>>>
>>> Cc: <stable@...r.kernel.org>
>>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>> Cc: Keith Busch <kbusch@...nel.org>
>>> Closes: https://www.spinics.net/lists/kernel/msg5563270.html
>>> Fixes: 6c6c47b063b5 ("mm, slab: call kvfree_rcu_barrier() from kmem_cache_destroy()"),
>>> Reported-by: Keith Busch <kbusch@...nel.org>
>>> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
>>
>> BTW, there is a path in RCU-tasks that involves queuing work on system_wq
>> which is !WQ_RECLAIM. While I don't anticipate an issue such as the one fixed
>> by this patch, I am wondering if we should move these to their own WQ_RECLAIM
>> queues for added robustness since otherwise that will result in CB invocation
>> (And thus memory freeing delays). Paul?
> 
> For RCU Tasks, the memory traffic has been much lower.  But maybe someday
> someone will drop a million trampolines all at once.  But let's see that
> problem before we fix some random problem that we believe will happen,
> but which proves to be only slightly related to the problem that actually
> does happen.  ;-)
> 


Fair enough. ;-)

thanks,

- Joel