Re: [PATCH v1 2/2] mm/slab/kvfree_rcu: Switch to WQ_MEM_RECLAIM wq

[Uladzislau Rezki <urezki@gmail.com>]

On Fri, Feb 28, 2025 at 03:42:02PM +0100, Vlastimil Babka wrote:
> 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@vger.kernel.org>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 
> stable is sufficient, no need for greg himself too
> 
> > Cc: Keith Busch <kbusch@kernel.org>
> > Closes: https://www.spinics.net/lists/kernel/msg5563270.html
> 
> lore pls :)
> 
Thanks, got it. I tried but did not find the link :)

> > Fixes: 6c6c47b063b5 ("mm, slab: call kvfree_rcu_barrier() from kmem_cache_destroy()"),
> > Reported-by: Keith Busch <kbusch@kernel.org>
> > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> 
> fixed locally and pushed to slab/for-next-fixes
> thanks!
>
Thanks!

--
Uladzislau Rezki