linux-kernel - Re: [PATCH v19 2/3] scsi: ufs: L2P map management for HPB read

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Date:   Mon, 08 Feb 2021 16:34:33 +0800
From:   Can Guo <cang@...eaurora.org>
To:     daejun7.park@...sung.com
Cc:     Greg KH <gregkh@...uxfoundation.org>, avri.altman@....com,
        jejb@...ux.ibm.com, martin.petersen@...cle.com,
        asutoshd@...eaurora.org, stanley.chu@...iatek.com,
        huobean@...il.com, bvanassche@....org,
        ALIM AKHTAR <alim.akhtar@...sung.com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sung-Jun Park <sungjun07.park@...sung.com>,
        yongmyung lee <ymhungry.lee@...sung.com>,
        Jinyoung CHOI <j-young.choi@...sung.com>,
        BoRam Shin <boram.shin@...sung.com>,
        SEUNGUK SHIN <seunguk.shin@...sung.com>
Subject: Re: [PATCH v19 2/3] scsi: ufs: L2P map management for HPB read

On 2021-02-08 16:03, Daejun Park wrote:
>> @@ -342,13 +1208,14 @@ void ufshpb_suspend(struct ufs_hba *hba)
>> >  	struct scsi_device *sdev;
>> >
>> >  	shost_for_each_device(sdev, hba->host) {
>> > -		hpb = sdev->hostdata;
>> > +		hpb = ufshpb_get_hpb_data(sdev);
>> >  		if (!hpb)
>> >  			continue;
>> >
>> >  		if (ufshpb_get_state(hpb) != HPB_PRESENT)
>> >  			continue;
>> >  		ufshpb_set_state(hpb, HPB_SUSPEND);
>> > +		ufshpb_cancel_jobs(hpb);
>> 
>> Here may have a dead lock problem - in the case of runtime suspend,
>> when ufshpb_suspend() is invoked, all of hba's children scsi devices
>> are in RPM_SUSPENDED state. When this line tries to cancel a running
>> map work, i.e. when ufshpb_get_map_req() calls below lines, it will
>> be stuck at blk_queue_enter().
>> 
>> req = blk_get_request(hpb->sdev_ufs_lu->request_queue,
>> 		      REQ_OP_SCSI_IN, 0);
>> 
>> Please check block layer power management, and see also commit 
>> d55d15a33
>> ("scsi: block: Do not accept any requests while suspended").
> 
> I am agree with your comment.
> How about add BLK_MQ_REQ_NOWAIT flag on blk_get_request() to avoid 
> hang?
> 

That won't work - BLK_MQ_REQ_NOWAIT allows one to fast fail from 
blk_mq_get_tag(),
but blk_queue_enter() comes before __blk_mq_alloc_request();

Regards,

Can Guo.

> Thanks,
> Daejun