linux-kernel - Re: [PATCH v5 1/7] scsi: ufs: Add "wb_on" sysfs node to control WB on/off

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Date:   Tue, 22 Dec 2020 21:57:12 +0100
From:   Bean Huo <huobean@...il.com>
To:     Can Guo <cang@...eaurora.org>,
        Stanley Chu <stanley.chu@...iatek.com>
Cc:     alim.akhtar@...sung.com, avri.altman@....com,
        asutoshd@...eaurora.org, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, beanhuo@...ron.com, bvanassche@....org,
        tomas.winkler@...el.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/7] scsi: ufs: Add "wb_on" sysfs node to control WB
 on/off

On Tue, 2020-12-22 at 14:12 +0800, Can Guo wrote:
> > > +            return -EOPNOTSUPP;
> > > +
> > > +    if (kstrtouint(buf, 0, &wb_enable))
> > > +            return -EINVAL;
> > > +
> > > +    if (wb_enable != 0 && wb_enable != 1)
> > > +            return -EINVAL;
> > > +
> > > +    pm_runtime_get_sync(hba->dev);
> > > +    res = ufshcd_wb_ctrl(hba, wb_enable);
> > 
> > May this operation race with UFS shutdown flow?
> > 
> > To be more clear, ufshcd_wb_ctrl() here may be executed after host 
> > clock
> > is disabled by shutdown flow?
> > 
> > If yes, we need to avoid it.
> 
> I have the same doubt - can user still access sysfs nodes after
> system
> starts to run shutdown routines? If yes, then we need to remove all
> UFS
> sysfs nodes in ufshcd_shutdown().
> 

No, we shouldn't do in this way, user space complains this. I think
the nodes in the sysfs can be shileded write, but the nodes shouldn't
be flash of its presence frequently.

Thanks,
Bean 


> Thanks,
> 
> Can Guo.