linux-kernel - Re: [PATCH] usb: uas: fix usb subsystem hang after power off hub port

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Date:   Fri, 8 Mar 2019 12:33:14 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Oliver Neukum <oneukum@...e.com>
cc:     Kento.A.Kobayashi@...y.com, <gregkh@...uxfoundation.org>,
        <usb-storage@...ts.one-eyed-alien.net>,
        <linux-kernel@...r.kernel.org>, <linux-scsi@...r.kernel.org>,
        <linux-usb@...r.kernel.org>
Subject: Re: [PATCH] usb: uas: fix usb subsystem hang after power off hub
 port

On Fri, 8 Mar 2019, Oliver Neukum wrote:

> On Fr, 2019-03-08 at 09:13 +0000, Kento.A.Kobayashi@...y.com wrote:
> > The usb_reset_and_verify_device included in usb_reset_device fails
> > with -ENODEV after power off hub port, and the -ENODEV error will
> > be reported to uas_eh_bus_reset_handler and upper layer, so it
> > doesn't need to do rebind if -ENODEV happens.
> 
> Hi,
> 
> no I am sorry, that is an assumption you just cannot make.
> Anything can trigger a reset. That being SCSI is the common
> case certainly, but not the only case. And in those cases
> we cannot depend on upper layers doing the right thing, if
> we just ignore an error.
> 
> NACK
> 
> 	Sorry
> 		Oliver

Note that the reset routines in usb-storage do not make any exceptions
for -ENODEV.

Alan Stern