RE: scsi_set_medium_removal timeout issue

[Zengtao (B)]

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?

Zengtao 

>Alan Stern
>
>> I found there are two methods to workaround the issue:
>> 1. Change the timeout value of host scsi command
>> PREVENT_ALLOW_MEDIUM_REMOVAL to to about 60 seconds from 10
>seconds.
>> 2. Remove the fsg_lun_fsync_sub in the device's Mass storage gadget
>driver.
>>
>> Thanks
>>
>> Regards
>> zentao