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Date: Wed, 12 Apr 2023 08:50:29 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: "Zhang, Qiang1" <qiang1.zhang@...el.com>,
Boqun Feng <boqun.feng@...il.com>,
Qi Zheng <zhengqi.arch@...edance.com>
Cc: "42.hyeyoo@...il.com" <42.hyeyoo@...il.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"roman.gushchin@...ux.dev" <roman.gushchin@...ux.dev>,
"iamjoonsoo.kim@....com" <iamjoonsoo.kim@....com>,
"rientjes@...gle.com" <rientjes@...gle.com>,
"penberg@...nel.org" <penberg@...nel.org>,
"cl@...ux.com" <cl@...ux.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Zhao Gongyi <zhaogongyi@...edance.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Thomas Gleixner <tglx@...utronix.de>,
RCU <rcu@...r.kernel.org>,
"Paul E . McKenney" <paulmck@...nel.org>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] mm: slub: annotate kmem_cache_node->list_lock as
raw_spinlock
On 4/12/23 08:44, Zhang, Qiang1 wrote:
>>
>>
>> On 2023/4/11 22:19, Vlastimil Babka wrote:
>>> On 4/11/23 16:08, Qi Zheng wrote:
>>>>
>>>>
>>>> On 2023/4/11 21:40, Vlastimil Babka wrote:
>>>>> On 4/11/23 15:08, Qi Zheng wrote:
>>>>>> The list_lock can be held in the critical section of
>>>>>> raw_spinlock, and then lockdep will complain about it
>>>>>> like below:
>>>>>>
>>>>>> =============================
>>>>>> [ BUG: Invalid wait context ]
>>>>>> 6.3.0-rc6-next-20230411 #7 Not tainted
>>>>>> -----------------------------
>>>>>> swapper/0/1 is trying to lock:
>>>>>> ffff888100055418 (&n->list_lock){....}-{3:3}, at: ___slab_alloc+0x73d/0x1330
>>>>>> other info that might help us debug this:
>>>>>> context-{5:5}
>>>>>> 2 locks held by swapper/0/1:
>>>>>> #0: ffffffff824e8160 (rcu_tasks.cbs_gbl_lock){....}-{2:2}, at: cblist_init_generic+0x22/0x2d0
>>>>>> #1: ffff888136bede50 (&ACCESS_PRIVATE(rtpcp, lock)){....}-{2:2}, at: cblist_init_generic+0x232/0x2d0
>>>>>> stack backtrace:
>>>>>> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.3.0-rc6-next-20230411 #7
>>>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
>>>>>> Call Trace:
>>>>>> <TASK>
>>>>>> dump_stack_lvl+0x77/0xc0
>>>>>> __lock_acquire+0xa65/0x2950
>>>>>> ? arch_stack_walk+0x65/0xf0
>>>>>> ? arch_stack_walk+0x65/0xf0
>>>>>> ? unwind_next_frame+0x602/0x8d0
>>>>>> lock_acquire+0xe0/0x300
>>>>>> ? ___slab_alloc+0x73d/0x1330
>>>>>> ? find_usage_forwards+0x39/0x50
>>>>>> ? check_irq_usage+0x162/0xa70
>>>>>> ? __bfs+0x10c/0x2c0
>>>>>> _raw_spin_lock_irqsave+0x4f/0x90
>>>>>> ? ___slab_alloc+0x73d/0x1330
>>>>>> ___slab_alloc+0x73d/0x1330
>>>>>> ? fill_pool+0x16b/0x2a0
>>>>>> ? look_up_lock_class+0x5d/0x160
>>>>>> ? register_lock_class+0x48/0x500
>>>>>> ? __lock_acquire+0xabc/0x2950
>>>>>> ? fill_pool+0x16b/0x2a0
>>>>>> kmem_cache_alloc+0x358/0x3b0
>>>>>> ? __lock_acquire+0xabc/0x2950
>>>>>> fill_pool+0x16b/0x2a0
>>>>>> ? __debug_object_init+0x292/0x560
>>>>>> ? lock_acquire+0xe0/0x300
>>>>>> ? cblist_init_generic+0x232/0x2d0
>>>>>> __debug_object_init+0x2c/0x560
>>
>> This "__debug_object_init" is because INIT_WORK() is called in
>> cblist_init_generic(), so..
>>
>>>>>> cblist_init_generic+0x147/0x2d0
>>>>>> rcu_init_tasks_generic+0x15/0x190
>>>>>> kernel_init_freeable+0x6e/0x3e0
>>>>>> ? rest_init+0x1e0/0x1e0
>>>>>> kernel_init+0x1b/0x1d0
>>>>>> ? rest_init+0x1e0/0x1e0
>>>>>> ret_from_fork+0x1f/0x30
>>>>>> </TASK>
>>>>>>
>>>>>> The fill_pool() can only be called in the !PREEMPT_RT kernel
>>>>>> or in the preemptible context of the PREEMPT_RT kernel, so
>>>>>> the above warning is not a real issue, but it's better to
>>>>>> annotate kmem_cache_node->list_lock as raw_spinlock to get
>>>>>> rid of such issue.
>>>>>
>>>>> + CC some RT and RCU people
>>>>
>>>> Thanks.
>>>>
>>>>>
>>>>> AFAIK raw_spinlock is not just an annotation, but on RT it changes the
>>>>> implementation from preemptible mutex to actual spin lock, so it would be
>>>>
>>>> Yeah.
>>>>
>>>>> rather unfortunate to do that for a spurious warning. Can it be somehow
>>>>> fixed in a better way?
>>
>> ... probably a better fix is to drop locks and call INIT_WORK(), or make
>> the cblist_init_generic() lockless (or part lockless), given it's just
>> initializing the cblist, it's probably doable. But I haven't taken a
>> careful look yet.
>>
>
>
> This is just one of the paths that triggers an invalid wait, the following paths can also trigger:
>
> [ 129.914547] [ BUG: Invalid wait context ]
> [ 129.914775] 6.3.0-rc1-yocto-standard+ #2 Not tainted
> [ 129.915044] -----------------------------
> [ 129.915272] kworker/2:0/28 is trying to lock:
> [ 129.915516] ffff88815660f570 (&c->lock){-.-.}-{3:3}, at: ___slab_alloc+0x68/0x12e0
> [ 129.915967] other info that might help us debug this:
> [ 129.916241] context-{5:5}
> [ 129.916392] 3 locks held by kworker/2:0/28:
> [ 129.916642] #0: ffff888100084d48 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x515/0xba0
> [ 129.917145] #1: ffff888100c17dd0 ((work_completion)(&(&krcp->monitor_work)->work)){+.+.}-{0:0}, at: process_on0
> [ 129.917758] #2: ffff8881565f8508 (krc.lock){....}-{2:2}, at: kfree_rcu_monitor+0x29f/0x810
> [ 129.918207] stack backtrace:
> [ 129.918374] CPU: 2 PID: 28 Comm: kworker/2:0 Not tainted 6.3.0-rc1-yocto-standard+ #2
> [ 129.918784] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.1-0-g3208b098f51a-prebuilt.qemu.o4
> [ 129.919397] Workqueue: events kfree_rcu_monitor
> [ 129.919662] Call Trace:
> [ 129.919812] <TASK>
> [ 129.919941] dump_stack_lvl+0x64/0xb0
> [ 129.920171] dump_stack+0x10/0x20
> [ 129.920372] __lock_acquire+0xeb8/0x3a80
> [ 129.920603] ? ret_from_fork+0x2c/0x50
> [ 129.920824] ? __pfx___lock_acquire+0x10/0x10
> [ 129.921068] ? unwind_next_frame.part.0+0x1ba/0x3c0
> [ 129.921343] ? ret_from_fork+0x2c/0x50
> [ 129.921573] ? __this_cpu_preempt_check+0x13/0x20
> [ 129.921847] lock_acquire+0x194/0x480
> [ 129.922060] ? ___slab_alloc+0x68/0x12e0
> [ 129.922293] ? __pfx_lock_acquire+0x10/0x10
> [ 129.922529] ? __pfx_mark_lock.part.0+0x10/0x10
> [ 129.922778] ? __kasan_check_read+0x11/0x20
> [ 129.922998] ___slab_alloc+0x9a/0x12e0
> [ 129.923222] ? ___slab_alloc+0x68/0x12e0
> [ 129.923452] ? __pfx_mark_lock.part.0+0x10/0x10
> [ 129.923706] ? __kasan_check_read+0x11/0x20
> [ 129.923937] ? fill_pool+0x22a/0x370
> [ 129.924161] ? __lock_acquire+0xf5b/0x3a80
> [ 129.924387] ? fill_pool+0x22a/0x370
> [ 129.924590] __slab_alloc.constprop.0+0x5b/0x90
> [ 129.924832] kmem_cache_alloc+0x296/0x3d0
> [ 129.925073] ? fill_pool+0x22a/0x370
> [ 129.925291] fill_pool+0x22a/0x370
> [ 129.925495] ? __pfx_fill_pool+0x10/0x10
> [ 129.925718] ? __pfx___lock_acquire+0x10/0x10
> [ 129.926034] ? __kasan_check_read+0x11/0x20
> [ 129.926269] ? check_chain_key+0x200/0x2b0
> [ 129.926503] __debug_object_init+0x82/0x8c0
> [ 129.926734] ? __pfx_lock_release+0x10/0x10
> [ 129.926984] ? __pfx___debug_object_init+0x10/0x10
> [ 129.927249] ? __kasan_check_read+0x11/0x20
> [ 129.927498] ? do_raw_spin_unlock+0x9c/0x100
> [ 129.927758] debug_object_activate+0x2d1/0x2f0
> [ 129.928022] ? __pfx_debug_object_activate+0x10/0x10
> [ 129.928300] ? __this_cpu_preempt_check+0x13/0x20
> [ 129.928583] __call_rcu_common.constprop.0+0x94/0xeb0
> [ 129.928897] ? __this_cpu_preempt_check+0x13/0x20
> [ 129.929186] ? __pfx_rcu_work_rcufn+0x10/0x10
> [ 129.929459] ? __pfx___call_rcu_common.constprop.0+0x10/0x10
> [ 129.929803] ? __pfx_lock_acquired+0x10/0x10
> [ 129.930067] ? __pfx_do_raw_spin_trylock+0x10/0x10
> [ 129.930363] ? kfree_rcu_monitor+0x29f/0x810
> [ 129.930627] call_rcu+0xe/0x20
> [ 129.930821] queue_rcu_work+0x4f/0x60
> [ 129.931050] kfree_rcu_monitor+0x5d3/0x810
> [ 129.931302] ? __pfx_kfree_rcu_monitor+0x10/0x10
> [ 129.931587] ? __this_cpu_preempt_check+0x13/0x20
> [ 129.931878] process_one_work+0x607/0xba0
> [ 129.932129] ? __pfx_process_one_work+0x10/0x10
> [ 129.932408] ? worker_thread+0xd6/0x710
> [ 129.932653] worker_thread+0x2d4/0x710
> [ 129.932888] ? __pfx_worker_thread+0x10/0x10
> [ 129.933154] kthread+0x18b/0x1c0
> [ 129.933363] ? __pfx_kthread+0x10/0x10
> [ 129.933598] ret_from_fork+0x2c/0x50
> [ 129.933825] </TASK>
>
> Maybe no need to convert ->list_lock to raw_spinlock.
>
> --- a/lib/debugobjects.c
> +++ b/lib/debugobjects.c
> @@ -562,10 +562,10 @@ __debug_object_init(void *addr, const struct debug_obj_descr *descr, int onstack
> unsigned long flags;
>
> /*
> - * On RT enabled kernels the pool refill must happen in preemptible
> + * The pool refill must happen in preemptible
> * context:
> */
> - if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible())
> + if (preemptible())
> fill_pool();
+CC Peterz
Aha so this is in fact another case where the code is written with
actual differences between PREEMPT_RT and !PREEMPT_RT in mind, but
CONFIG_PROVE_RAW_LOCK_NESTING always assumes PREEMPT_RT?
> db = get_bucket((unsigned long) addr);
>
>
>
> Thanks
> Zqiang
>
>>
>>
>> Regards,
>> Boqun
>>
>>>>
>>>> It's indeed unfortunate for the warning in the commit message. But
>>>> functions like kmem_cache_alloc(GFP_ATOMIC) may indeed be called
>>>> in the critical section of raw_spinlock or in the hardirq context, which
>>>
>>> Hmm, I thought they may not, actually.
>>>
>>>> will cause problem in the PREEMPT_RT kernel. So I still think it is
>>>> reasonable to convert kmem_cache_node->list_lock to raw_spinlock type.
>>>
>>> It wouldn't be the complete solution anyway. Once we allow even a GFP_ATOMIC
>>> slab allocation for such context, it means also page allocation can happen
>>> to refill the slabs, so lockdep will eventually complain about zone->lock,
>>> and who knows what else.
>>
>> Oh, indeed. :(
>>
>>>
>>>> In addition, there are many fix patches for this kind of warning in the
>>>> git log, so I also think there should be a general and better solution. :)
>>>
>>> Maybe, but given above, I doubt it's this one.
>>>
>>>>
>>>>>
>>>>
>>>
>>
>> --
>> Thanks,
>> Qi
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