linux-kernel - Re: [PATCH RFC 8/9] block, bfq: move forward __bfq_weights_tree

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Date:   Sat, 11 Dec 2021 10:18:53 +0800
From:   "yukuai (C)" <yukuai3@...wei.com>
To:     Paolo Valente <paolo.valente@...aro.org>
CC:     Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        <cgroups@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, <yi.zhang@...wei.com>
Subject: Re: [PATCH RFC 8/9] block, bfq: move forward
 __bfq_weights_tree_remove()

在 2021/12/10 18:00, Paolo Valente 写道:
> 
> 
>> Il giorno 27 nov 2021, alle ore 11:11, Yu Kuai <yukuai3@...wei.com> ha scritto:
>>
>> Prepare to decrease 'num_groups_with_pending_reqs' earlier.
>>
>> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
>> ---
>> block/bfq-iosched.c | 13 +++++--------
>> 1 file changed, 5 insertions(+), 8 deletions(-)
>>
>> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
>> index e3c31db4bffb..4239b3996e23 100644
>> --- a/block/bfq-iosched.c
>> +++ b/block/bfq-iosched.c
>> @@ -882,6 +882,10 @@ void bfq_weights_tree_remove(struct bfq_data *bfqd,
>> {
>> 	struct bfq_entity *entity = bfqq->entity.parent;
>>
>> +	bfqq->ref++;
>> +	__bfq_weights_tree_remove(bfqd, bfqq,
>> +				  &bfqd->queue_weights_tree);
>> +
>> 	for_each_entity(entity) {
>> 		struct bfq_sched_data *sd = entity->my_sched_data;
>>
>> @@ -916,14 +920,7 @@ void bfq_weights_tree_remove(struct bfq_data *bfqd,
>> 		}
>> 	}
>>
>> -	/*
>> -	 * Next function is invoked last, because it causes bfqq to be
>> -	 * freed if the following holds: bfqq is not in service and
>> -	 * has no dispatched request. DO NOT use bfqq after the next
>> -	 * function invocation.
>> -	 */
>> -	__bfq_weights_tree_remove(bfqd, bfqq,
>> -				  &bfqd->queue_weights_tree);
>> +	bfq_put_queue(bfqq);
>> }
>>
> 
> why it is not dangerous any longer to invoke __bfq_weights_tree_remove earlier, and the comment can be removed?

Hi, Paolo

Here I grab an additional ref to the bfqq, thus the bfqq is ensured not
to be free before bfq_put_queue() at the end of the function.

Maybe some comments is more appropriate.

Thanks,
Kuai
> 
> Paolo
> 
>> /*
>> -- 
>> 2.31.1
>>
> 
> .
>