linux-kernel - Re: [PATCH -next] block/wbt: fix negative inflight counter when remove scsi device

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Date:   Tue, 14 Dec 2021 12:25:07 +0800
From:   QiuLaibin <qiulaibin@...wei.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     <axboe@...nel.dk>, <yi.zhang@...wei.com>,
        <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] block/wbt: fix negative inflight counter when
 remove scsi device


On 2021/12/14 1:16, Christoph Hellwig wrote:
> On Mon, Dec 13, 2021 at 12:09:07PM +0800, Laibin Qiu wrote:
>> Submit_bio
>>                                                           scsi_remove_device
>>                                                           sd_remove
>>                                                           del_gendisk
>>                                                           blk_unregister_queue
>>                                                           elv_unregister_queue
>>                                                           wbt_enable_default
>>                                                           <= Set rwb->enable_state (ON)
>> q_qos_track
>> <= rwb->enable_state (ON)
>> ^^^^^^ this request will mark WBT_TRACKED without inflight add and will
>> lead to drop rqw->inflight to -1 in wbt_done() which will trigger IO hung.
>>
>> Fix this by judge whether QUEUE_FLAG_REGISTERED is marked to distinguish
>> scsi remove scene.
>> Fixes: 76a8040817b4b ("blk-wbt: make sure throttle is enabled properly")
>> Signed-off-by: Laibin Qiu <qiulaibin@...wei.com>
>> ---
>>   block/blk-wbt.c | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/block/blk-wbt.c b/block/blk-wbt.c
>> index 3ed71b8da887..537f77bb1365 100644
>> --- a/block/blk-wbt.c
>> +++ b/block/blk-wbt.c
>> @@ -637,6 +637,10 @@ void wbt_enable_default(struct request_queue *q)
>>   {
>>   	struct rq_qos *rqos = wbt_rq_qos(q);
>>   
>> +	/* Queue not registered? Maybe shutting down... */
>> +	if (!blk_queue_registered(q))
>> +		return;
> 
> Wouldn't it make more sense to simply not call wbt_enable_default from
> elv_unregister_queue?
> .
> 

Refer to your opinion, I will post another version of V2.
Please take a look again.