linux-kernel - Re: [PATCH] USB:UAS:return ENODEV when submit urbs fail with device not attached.

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Date: Thu, 22 Feb 2024 10:47:07 +0100
From: Oliver Neukum <oneukum@...e.com>
To: Weitao Wang <WeitaoWang-oc@...oxin.com>, oneukum@...e.com,
 stern@...land.harvard.edu, gregkh@...uxfoundation.org,
 linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-scsi@...r.kernel.org, usb-storage@...ts.one-eyed-alien.net
Cc: WeitaoWang@...oxin.com
Subject: Re: [PATCH] USB:UAS:return ENODEV when submit urbs fail with device
 not attached.

On 22.02.24 17:54, Weitao Wang wrote:
> In the scenario of entering hibernation with udisk in the system, if the
> udisk was gone or resume fail in the thaw phase of hibernation. Its state
> will be set to NOTATTACHED. However, usb_hub_wq was already freezed and
> can't not handle disconnect event. Then, sync cache SCSI command will be
> sent to this udisk on the poweroff phase of hibernation, that will cause

Wait, this seems like a contradiction. Are we in thaw or are we powering off?

> uas_submit_urbs to be called to submit URB to sense/data/cmd pipe. Then,
> usb_submit_urb return value -ENODEV when device was set to NOTATTACHED
> state. However, uas_submit_urbs always return "SCSI_MLQUEUE_DEVICE_BUSY"
> regardless of the reason for submission failure.That will lead the SCSI
> layer go into an ugly loop and system fail to go into hibernation.

The thing is that the SCSI documentation explicitly tells us to return
either SCSI_MLQUEUE_DEVICE_BUSY or SCSI_MLQUEUE_HOST_BUSY. Now, it makes
sense to tell the SCSI laer that a device or host is gone for good,
if we know that. But we cannot just introduce new error returns on our own.

This needs to be addressed. That means that the SCSI layer or at the
very least the documentation needs to be fixed. Frankly, this is not strictly
speaking a UAS issue. Any thing hotunpluggable should have this issue.

	Regards
		Oliver