Re: [RFC PATCH] block: Make request_queue lockdep splats show up earlier

[Bart Van Assche <bvanassche@acm.org>]

On 3/17/25 11:13 AM, Thomas Hellström wrote:
> On Mon, 2025-03-17 at 10:37 -0700, Bart Van Assche wrote:
>> On 3/17/25 10:11 AM, Thomas Hellström wrote:
>>> diff --git a/block/blk-core.c b/block/blk-core.c
>>> index d6c4fa3943b5..4aa439309406 100644
>>> --- a/block/blk-core.c
>>> +++ b/block/blk-core.c
>>> @@ -455,6 +455,12 @@ struct request_queue *blk_alloc_queue(struct
>>> queue_limits *lim, int node_id)
>>>    	lockdep_init_map(&q->q_lockdep_map, "&q-
>>>> q_usage_counter(queue)",
>>>    			 &q->q_lock_cls_key, 0);
>>>    
>>> +	/* Prime io_lockdep_map as reclaim tainted */
>>> +	fs_reclaim_acquire(GFP_KERNEL);
>>> +	rwsem_acquire_read(&q->io_lockdep_map, 0, 0, _RET_IP_);
>>> +	rwsem_release(&q->io_lockdep_map, _RET_IP_);
>>> +	fs_reclaim_release(GFP_KERNEL);
>>> +
>>>    	q->nr_requests = BLKDEV_DEFAULT_RQ;
>>>    
>>>    	return q;
>>
>> Hmm ... my understanding is that it is fine if FS code calls block
>> layer
>> code but also that block layer code never should call FS code.
> 
> That added code only mimics the locking sequence that happens during
> reclaim with the existing code to register the locking order expected
> by the reclaim code. If anything violates that, lockdep splat [2] will
> appear.
> 
> So I'm not quite following your comment?
Shouldn't the above code be added in the VFS code rather than in the
block layer?

Thanks,

Bart.