linux-kernel - RE: [PATCH v3 1/1] scsi: pm: Balance pm_only counter of request queue during system resume

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Message-ID: <BYAPR04MB462931F8DF1112CAF7F80CA4FCAA0@BYAPR04MB4629.namprd04.prod.outlook.com>
Date:   Thu, 30 Apr 2020 09:11:17 +0000
From:   Avri Altman <Avri.Altman@....com>
To:     Bart Van Assche <bvanassche@....org>,
        Can Guo <cang@...eaurora.org>,
        "asutoshd@...eaurora.org" <asutoshd@...eaurora.org>,
        "nguyenb@...eaurora.org" <nguyenb@...eaurora.org>,
        "hongwus@...eaurora.org" <hongwus@...eaurora.org>,
        "rnayak@...eaurora.org" <rnayak@...eaurora.org>,
        "stanley.chu@...iatek.com" <stanley.chu@...iatek.com>,
        "alim.akhtar@...sung.com" <alim.akhtar@...sung.com>,
        "beanhuo@...ron.com" <beanhuo@...ron.com>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "kernel-team@...roid.com" <kernel-team@...roid.com>,
        "saravanak@...gle.com" <saravanak@...gle.com>,
        "salyzyn@...gle.com" <salyzyn@...gle.com>
CC:     "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3 1/1] scsi: pm: Balance pm_only counter of request queue
 during system resume

 
> 
> On 2020-04-29 21:10, Can Guo wrote:
> > During system resume, scsi_resume_device() decreases a request queue's
> > pm_only counter if the scsi device was quiesced before. But after that,
> > if the scsi device's RPM status is RPM_SUSPENDED, the pm_only counter is
> > still held (non-zero). Current scsi resume hook only sets the RPM status
> > of the scsi device and its request queue to RPM_ACTIVE, but leaves the
> > pm_only counter unchanged. This may make the request queue's pm_only
> > counter remain non-zero after resume hook returns, hence those who are
> > waiting on the mq_freeze_wq would never be woken up. Fix this by calling
> > blk_post_runtime_resume() if pm_only is non-zero to balance the pm_only
> > counter which is held by the scsi device's RPM ops.
> 
> How was this issue discovered? How has this patch been tested?

I think this insight was originally gained as part of commit fb276f770118
(scsi: ufs: Enable block layer runtime PM for well-known logical units)

But I will let Can reply on that.

Thanks,
Avri

> 
> Thanks,
> 
> Bart.