Re: BUG: MAX_LOCKDEP_KEYS too low!

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 23/01/2021 02:30, Tetsuo Handa wrote:
> On 2021/01/22 22:28, Tetsuo Handa wrote:
>> On 2021/01/22 21:10, Dmitry Vyukov wrote:
>>> On Fri, Jan 22, 2021 at 1:03 PM Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
>>>>
>>>>
>>>>
>>>> On 22/01/2021 21:30, Tetsuo Handa wrote:
>>>>> On 2021/01/22 18:16, Dmitry Vyukov wrote:
>>>>>> The reproducer only does 2 bpf syscalls, so something is slowly leaking in bpf.
>>>>>> My first suspect would be one of these. Since workqueue is async, it
>>>>>> may cause such slow drain that happens only when tasks are spawned
>>>>>> fast. I don't know if there is a procfs/debugfs introspection file to
>>>>>> monitor workqueue lengths to verify this hypothesis.
>>>>>
>>>>> If you can reproduce locally, you can call show_workqueue_state()
>>>>> (part of SysRq-t) when hitting the limit.
>>>>>
>>>>> --- a/kernel/locking/lockdep.c
>>>>> +++ b/kernel/locking/lockdep.c
>>>>> @@ -1277,6 +1277,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
>>>>>
>>>>>                   print_lockdep_off("BUG: MAX_LOCKDEP_KEYS too low!");
>>>>>                   dump_stack();
>>>>> +               show_workqueue_state();
>>>>>                   return NULL;
>>>>>           }
>>>>>           nr_lock_classes++;
>>>>>
>>>>
>>>>
>>>>
>>>> Here is the result:
>>>> https://pastebin.com/rPn0Cytu
>>>
>>> Do you mind posting this publicly?
>>> Yes, it seems that bpf_map_free_deferred is the problem (11138
>>> outstanding callbacks).
>>>
>>
>> Wow. Horribly stuck queue. I guess BPF wants to try WQ created by
>>
>>    alloc_workqueue("bpf_free_wq", WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 0);
>>
>> rather than system_wq . You can add Tejun Heo <tj@kernel.org> for WQ.
>>
>> Anyway, please post your result to ML.



https://pastebin.com/JfrmzguK is with the patch below applied. Seems 
less output. Interestingly when I almost hit "send", OOM kicked in and 
tried killing a bunch of "maxlockdep" processes (my test case):

[  891.037315] [  31007]     0 31007      281        5    49152        0 
          1000 maxlockdep
[  891.037540] [  31009]     0 31009      281        5    49152        0 
          1000 maxlockdep
[  891.037760] [  31012]     0 31012      281        5    49152        0 
          1000 maxlockdep
[  891.037980] [  31013]     0 31013      281        5    47104        0 
             0 maxlockdep
[  891.038210] [  31014]     0 31014      281        5    49152        0 
          1000 maxlockdep
[  891.038429] [  31018]     0 31018      281        5    47104        0 
             0 maxlockdep
[  891.038652] [  31019]     0 31019      281        5    49152        0 
          1000 maxlockdep
[  891.038874] [  31020]     0 31020      281        5    49152        0 
          1000 maxlockdep
[  891.039095] [  31021]     0 31021      281        5    49152        0 
          1000 maxlockdep
[  891.039317] [  31022]     0 31022      281        5    47104        0 
             0 maxlockdep




And (re)adding LKML and Tejun as suggested. Thanks,


>>
> 
> Does this patch (which is only compile tested) reduce number of pending works
> when hitting "BUG: MAX_LOCKDEP_KEYS too low!" ?
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 07cb5d15e743..c6c6902090f0 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -41,6 +41,7 @@ struct bpf_local_storage_map;
>   struct kobject;
>   struct mem_cgroup;
>   
> +extern struct workqueue_struct *bpf_free_wq;
>   extern struct idr btf_idr;
>   extern spinlock_t btf_idr_lock;
>   extern struct kobject *btf_kobj;
> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> index 1f8453343bf2..8b1cf6aab089 100644
> --- a/kernel/bpf/arraymap.c
> +++ b/kernel/bpf/arraymap.c
> @@ -994,7 +994,7 @@ static void prog_array_map_clear(struct bpf_map *map)
>   	struct bpf_array_aux *aux = container_of(map, struct bpf_array,
>   						 map)->aux;
>   	bpf_map_inc(map);
> -	schedule_work(&aux->work);
> +	queue_work(bpf_free_wq, &aux->work);
>   }
>   
>   static struct bpf_map *prog_array_map_alloc(union bpf_attr *attr)
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index 96555a8a2c54..f272844163df 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -160,7 +160,7 @@ static void cgroup_bpf_release_fn(struct percpu_ref *ref)
>   	struct cgroup *cgrp = container_of(ref, struct cgroup, bpf.refcnt);
>   
>   	INIT_WORK(&cgrp->bpf.release_work, cgroup_bpf_release);
> -	queue_work(system_wq, &cgrp->bpf.release_work);
> +	queue_work(bpf_free_wq, &cgrp->bpf.release_work);
>   }
>   
>   /* Get underlying bpf_prog of bpf_prog_list entry, regardless if it's through
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 261f8692d0d2..9d76c0d77687 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -34,6 +34,15 @@
>   #include <linux/log2.h>
>   #include <asm/unaligned.h>
>   
> +struct workqueue_struct *bpf_free_wq;
> +
> +static int __init bpf_free_wq_init(void)
> +{
> +	bpf_free_wq = alloc_workqueue("bpf_free_wq", WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 0);
> +	return 0;
> +}
> +subsys_initcall(bpf_free_wq_init);
> +
>   /* Registers */
>   #define BPF_R0	regs[BPF_REG_0]
>   #define BPF_R1	regs[BPF_REG_1]
> @@ -2152,7 +2161,7 @@ void bpf_prog_free(struct bpf_prog *fp)
>   	if (aux->dst_prog)
>   		bpf_prog_put(aux->dst_prog);
>   	INIT_WORK(&aux->work, bpf_prog_free_deferred);
> -	schedule_work(&aux->work);
> +	queue_work(bpf_free_wq, &aux->work);
>   }
>   EXPORT_SYMBOL_GPL(bpf_prog_free);
>   
> diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
> index 747313698178..6507cc8263fc 100644
> --- a/kernel/bpf/cpumap.c
> +++ b/kernel/bpf/cpumap.c
> @@ -515,7 +515,7 @@ static void __cpu_map_entry_replace(struct bpf_cpu_map *cmap,
>   	if (old_rcpu) {
>   		call_rcu(&old_rcpu->rcu, __cpu_map_entry_free);
>   		INIT_WORK(&old_rcpu->kthread_stop_wq, cpu_map_kthread_stop);
> -		schedule_work(&old_rcpu->kthread_stop_wq);
> +		queue_work(bpf_free_wq, &old_rcpu->kthread_stop_wq);
>   	}
>   }
>   
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index e5999d86c76e..084b903b4ee6 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -477,7 +477,7 @@ static void __bpf_map_put(struct bpf_map *map, bool do_idr_lock)
>   		bpf_map_free_id(map, do_idr_lock);
>   		btf_put(map->btf);
>   		INIT_WORK(&map->work, bpf_map_free_deferred);
> -		schedule_work(&map->work);
> +		queue_work(bpf_free_wq, &map->work);
>   	}
>   }
>   
> @@ -2343,7 +2343,7 @@ void bpf_link_put(struct bpf_link *link)
>   
>   	if (in_atomic()) {
>   		INIT_WORK(&link->work, bpf_link_put_deferred);
> -		schedule_work(&link->work);
> +		queue_work(bpf_free_wq, &link->work);
>   	} else {
>   		bpf_link_free(link);
>   	}
> 

-- 
Alexey