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

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Message-ID: <c4d0005d-ae34-40d4-80a0-67ca904cdae1@suse.cz>
Date: Fri, 28 Feb 2025 15:42:02 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: "Uladzislau Rezki (Sony)" <urezki@...il.com>, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: 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 2/28/25 13:13, 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>

stable is sufficient, no need for greg himself too

> Cc: Keith Busch <kbusch@...nel.org>
> Closes: https://www.spinics.net/lists/kernel/msg5563270.html

lore pls :)

> 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>

fixed locally and pushed to slab/for-next-fixes
thanks!