linux-kernel - Re: [PATCH] scsi: sd: add runtime pm to open / release

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Date:   Wed, 29 Jul 2020 07:46:35 -0700
From:   James Bottomley <jejb@...ux.ibm.com>
To:     Alan Stern <stern@...land.harvard.edu>,
        Martin Kepplinger <martin.kepplinger@...i.sm>
Cc:     Bart Van Assche <bvanassche@....org>,
        Can Guo <cang@...eaurora.org>, martin.petersen@...cle.com,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...i.sm
Subject: Re: [PATCH] scsi: sd: add runtime pm to open / release

On Wed, 2020-07-29 at 10:32 -0400, Alan Stern wrote:
> On Wed, Jul 29, 2020 at 04:12:22PM +0200, Martin Kepplinger wrote:
> > On 28.07.20 22:02, Alan Stern wrote:
> > > On Tue, Jul 28, 2020 at 09:02:44AM +0200, Martin Kepplinger
> > > wrote:
> > > > Hi Alan,
> > > > 
> > > > Any API cleanup is of course welcome. I just wanted to remind
> > > > you that the underlying problem: broken block device runtime
> > > > pm. Your initial proposed fix "almost" did it and mounting
> > > > works but during file access, it still just looks like a
> > > > runtime_resume is missing somewhere.
> > > 
> > > Well, I have tested that proposed fix several times, and on my
> > > system it's working perfectly.  When I stop accessing a drive it
> > > autosuspends, and when I access it again it gets resumed and
> > > works -- as you would expect.
> > 
> > that's weird. when I mount, everything looks good, "sda1". But as
> > soon as I cd to the mountpoint and do "ls" (on another SD card "ls"
> > works but actual file reading leads to the exact same errors), I
> > get:
> > 
> > [   77.474632] sd 0:0:0:0: [sda] tag#0 UNKNOWN(0x2003) Result:
> > hostbyte=0x00 driverbyte=0x08 cmd_age=0s
> > [   77.474647] sd 0:0:0:0: [sda] tag#0 Sense Key : 0x6 [current]
> > [   77.474655] sd 0:0:0:0: [sda] tag#0 ASC=0x28 ASCQ=0x0
> > [   77.474667] sd 0:0:0:0: [sda] tag#0 CDB: opcode=0x28 28 00 00 00
> > 60 40 00 00 01 00
> 
> This error report comes from the SCSI layer, not the block layer.

That sense code means "NOT READY TO READY CHANGE, MEDIUM MAY HAVE
CHANGED" so it sounds like it something we should be ignoring.  Usually
this signals a problem, like you changed the medium manually (ejected
the CD).  But in this case you can tell us to expect this by setting

sdev->expecting_cc_ua

And we'll retry.  I think you need to set this on all resumed devices.

James