linux-kernel - Re: [PATCH] usb: hub: Fix unhandled return value of usb_autopm_get

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Message-ID: <20200225191241.GA32410@lxhi-065.adit-jv.com>
Date:   Tue, 25 Feb 2020 20:12:41 +0100
From:   Eugeniu Rosca <erosca@...adit-jv.com>
To:     Alan Stern <stern@...land.harvard.edu>
CC:     <linux-usb@...r.kernel.org>, <linux-renesas-soc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "Lee, Chiasheng" <chiasheng.lee@...el.com>,
        Mathieu Malaterre <malat@...ian.org>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Hardik Gajjar <hgajjar@...adit-jv.com>,
        <scan-admin@...erity.com>, Eugeniu Rosca <erosca@...adit-jv.com>,
        Eugeniu Rosca <roscaeugeniu@...il.com>
Subject: Re: [PATCH] usb: hub: Fix unhandled return value of
 usb_autopm_get_interface()

Hi Alan,

Many thanks for the prompt review.

On Tue, Feb 25, 2020 at 10:32:32AM -0500, Alan Stern wrote:
> On Tue, 25 Feb 2020, Eugeniu Rosca wrote:
> > +		int r = usb_autopm_get_interface(intf);
> > +
> > +		if (!r)
> > +			hub->quirk_disable_autosuspend = 1;
> > +		else
> > +			dev_dbg(&intf->dev, "disable autosuspend err=%d\n", r);
> >  	}
> >  
> >  	if (hub_configure(hub, &desc->endpoint[0].desc) >= 0)
> 
> This change is not necessary, because the resume operation cannot fail
> at this point (interfaces are always powered-up during probe).

Agreed to avoid unneeded complexity.

> A better solution would be to call usb_autpm_get_interface_no_resume()
> instead.

Pushed to https://lore.kernel.org/lkml/20200225183057.31953-1-erosca@de.adit-jv.com

> 
> On the other hand, the other places that call
> usb_autopm_get_interface() without checking should be audited.  Some of
> them almost certainly need to be fixed.

A quick 'git grep' outputs below list of auditable candidates [1].

With no relevant devices at hand, I would avoid touching these drivers,
since oftentimes even legitimate patches introduce regressions w/o
testing.

If anybody volunteers with testing, I guess it should be quick to
either convert usb_autpm_get_interface to *_no_resume variant or
handle the return value in place in below instances.

[1] (v5.6-rc3) git grep -En "[^=]\s+usb_autopm_get_interface\("
  drivers/input/touchscreen/usbtouchscreen.c:1788:  usb_autopm_get_interface(intf);
  drivers/media/usb/stkwebcam/stk-webcam.c:628:     usb_autopm_get_interface(dev->interface);
  drivers/net/usb/hso.c:1308:                       usb_autopm_get_interface(serial->parent->interface);
  drivers/net/usb/r8152.c:5231:                     usb_autopm_get_interface(tp->intf);
  sound/usb/usx2y/us122l.c:192:                     usb_autopm_get_interface(iface);

-- 
Best Regards
Eugeniu Rosca