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

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Date:   Tue, 25 Feb 2020 14:39:23 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Eugeniu Rosca <erosca@...adit-jv.com>
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 <roscaeugeniu@...il.com>
Subject: Re: [PATCH] usb: hub: Fix unhandled return value of usb_autopm_get_interface()

On Tue, 25 Feb 2020, Eugeniu Rosca wrote:

> 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);

Your regular expression isn't right because it doesn't match lines
where the usb_autopm_get_interface() is preceded only by one whitespace
character (i.e., a tab).  It also will match lines where there are two
space characters between the = sign and the function name.  I think
what you want is more like "(^|[^=[:space:]])\s*" at the start of the
RE.

A revised search finds line 997 in drivers/usb/core/hub.c and lines
216, 269 in drivers/usb/core/port.c.  (I didn't try looking in any
other directories.)  AFAICT all three of these should check the return
value, although a error message in the kernel log probably isn't
needed.

Do you want to fix those instances up also, maybe merging them in with
the existing patch?

Alan Stern