RE: scsi_set_medium_removal timeout issue

[Alan Stern]

On Wed, 31 Oct 2018, Zengtao (B) wrote:

> Hi:
> 
> >-----Original Message-----
> >From: Alan Stern [mailto:stern@xxxxxxxxxxxxxxxxxxx]
> >Sent: Tuesday, October 30, 2018 10:08 PM
> >To: Zengtao (B) <prime.zeng@xxxxxxxxxxxxx>
> >Cc: jejb@xxxxxxxxxxxxxxxxxx; martin.petersen@xxxxxxxxxx;
> >gregkh@xxxxxxxxxxxxxxxxxxx; linux-scsi@xxxxxxxxxxxxxxx;
> >linux-kernel@xxxxxxxxxxxxxxx; linux-usb@xxxxxxxxxxxxxxx;
> >usb-storage@xxxxxxxxxxxxxxxxxxxxxxxx
> >Subject: Re: scsi_set_medium_removal timeout issue
> >
> >On Tue, 30 Oct 2018, Zengtao (B) wrote:
> >
> >> Hi
> >>
> >> I have recently met a scsi_set_medium_removal timeout issue, and it's
> >> related  to both SCSI and USB MASS storage.
> >> Since i am not an expert in either scsi or usb mass storage, i am
> >> writing to report the issue and ask for a solution from you guys.
> >>
> >> My test scenario is as follow:
> >> 1.Linux HOST-----Linux mass storage gadget(the back store is a flash
> >partition).
> >> 2.Host mount the device.
> >> 3.Host writes some data to the Mass storage device.
> >> 4.Host Unmount the device.
> >> Both Linux kernels(Host and Device) are Linux 4.9.
> >> Some has reported the same issue a long time ago, but it remains there.
> >> https://www.spinics.net/lists/linux-usb/msg53739.html
> >>
> >> For the issue itself, there is my observation:
> >> In the step 4, the Host will issue an
> >PREVENT_ALLOW_MEDIUM_REMOVAL scsi command.
> >> and and timeout happens due to the device 's very slow
> >fsg_lun_fsync_sub.
> >
> >Something is wrong here.  Before sending PREVENT-ALLOW MEDIUM
> >REMOVAL, the host should issue SYNCHRONIZE CACHE.  This will force
> >fsg_lun_fsync_sub to run, and the host should allow a long timeout for
> >this command.  Then when PREVENT-ALLOW MEDIUM REMOVAL is sent,
> >nothing will need to be flushed.
> >
> 
> Definitely, I haven't seen the SYNCHRONIZE CACHE from the host, it directly
> issued the PREVENT-ALLOW MEDIUM REMOVAL, so maybe something wrong
> with the scsi layer or something wrong with the mass storage class driver?

Or it could be something else.  Can you please post the dmesg log from
the host, showing what happens when the device is first plugged in?

Alan Stern