Re: [PATCH v11 4/4] xfs: replace mrlock_t with rw_semaphores

[Pavel Reichl <preichl@redhat.com>]

On 10/13/20 1:04 PM, Brian Foster wrote:
> On Mon, Oct 12, 2020 at 10:44:38PM +0200, Pavel Reichl wrote:
>>
>>
>> On 10/12/20 6:04 PM, Brian Foster wrote:
>>> ...
>>>> @@ -2863,8 +2875,20 @@ xfs_btree_split(
>>>>  	args.done = &done;
>>>>  	args.kswapd = current_is_kswapd();
>>>>  	INIT_WORK_ONSTACK(&args.work, xfs_btree_split_worker);
>>>> +	/*
>>>> +	 * Update lockdep's ownership information to reflect that we
>>>> +	 * will be transferring the ilock from this thread to the
>>>> +	 * worker.
>>>> +	 */
>>>
>>> Can we update this comment to explain why we need to do this? E.g., I'm
>>> assuming there's a lockdep splat somewhere down in the split worker
>>> without it, but it's not immediately clear where and so it might not be
>>> obvious if we're ever able to remove this.
>>
>> Hi, would something like this work for you?
>>
>> 	/*
>> +	 * Update lockdep's ownership information to reflect that we
>> +	 * will be transferring the ilock from this thread to the
>> +	 * worker (xfs_btree_split_worker() run via queue_work()).
>> +	 * If the ownership transfer would not happen lockdep would
>> +	 * assert in the worker thread because the ilock would be owned
>> +	 * by the original thread.
>> +	 */
>>
> 
> That doesn't really answer the question. Do you have a record of the
> lockdep error message that occurs without this state transfer, by
> chance?
> 
> Brian

Hi, please see this mail from Darrick - he hit the issue first - http://mail.spinics.net/lists/linux-xfs/msg38967.html

> 
>>
>