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 23:11:43 +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 21:57 +0100, Bean Huo wrote:
> > > 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.


Hi Can
Got your point, you don't want user space to interrupt UFS by sysyfs if
UFS is in power down mode. if this is true, insteading of removing all
sysfs node in ufshcd_shutdown, maybe just add this checkup before
accessing UFS device descriptors/flag/attributes/LU:

for example, for the device descriptor:


diff --git a/drivers/scsi/ufs/ufs-sysfs.c b/drivers/scsi/ufs/ufs-
sysfs.c       
index b3bf7fca00e5..881fe1c24a9f 100644
--- a/drivers/scsi/ufs/ufs-sysfs.c
+++ b/drivers/scsi/ufs/ufs-sysfs.c
@@ -262,6 +262,9 @@ static ssize_t ufs_sysfs_read_desc_param(struct
ufs_hba *hba,
        u8 desc_buf[8] = {0};
        int ret;
 
+       if (!ufshcd_is_ufs_dev_active(hba) ||
!ufshcd_is_link_active(hba))
+               return -EACCES;
+

Bean