Messages in this thread | | | Date | Wed, 12 Apr 2023 14:45:33 +0800 | Subject | Re: [PATCH] mm: slub: annotate kmem_cache_node->list_lock as raw_spinlock | From | Qi Zheng <> |
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On 2023/4/12 13:51, Boqun Feng wrote: > On Tue, Apr 11, 2023 at 10:25:06PM +0800, Qi Zheng 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..
Yes, a more precise call stack is as follows:
cblist_init_generic --> INIT_WORK --> lockdep_init_map --> lockdep_init_map_type --> register_lock_class --> init_data_structures_once --> init_rcu_head --> debug_object_init --> __debug_object_init
> >>>>>> 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 might be a doable solution for this warning, but I also saw another stacks like the following on v5.15:
[ 30.349171] Call Trace: [ 30.349171] <TASK> [ 30.349171] dump_stack_lvl+0x69/0x97 [ 30.349171] __lock_acquire+0x4a0/0x1aa0 [ 30.349171] lock_acquire+0x275/0x2e0 [ 30.349171] _raw_spin_lock_irqsave+0x4c/0x90 [ 30.349171] ___slab_alloc.constprop.95+0x3ea/0xa80 [ 30.349171] __slab_alloc.isra.89.constprop.94+0x1c/0x30 [ 30.349171] kmem_cache_alloc+0x2bd/0x320 [ 30.349171] fill_pool+0x1b2/0x2d0 [ 30.349171] __debug_object_init+0x2c/0x500 [ 30.349171] debug_object_activate+0x136/0x200 [ 30.349171] add_timer+0x10b/0x170 [ 30.349171] queue_delayed_work_on+0x63/0xa0 [ 30.349171] init_mm_internals+0x226/0x2b0 [ 30.349171] kernel_init_freeable+0x82/0x24e [ 30.349171] kernel_init+0x17/0x140 [ 30.349171] ret_from_fork+0x1f/0x30 [ 30.349171] </TASK>
So I'm a bit confused whether to fix individual cases or should there be a general solution.
Thanks, Qi
> > 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
-- Thanks, Qi
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