linux-kernel - Re: [RFC/PATCH] usb/xhci: avoid kernel panic on xhci

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Date:	Wed, 8 Jan 2014 11:53:34 -0800
From:	David Cohen <david.a.cohen@...ux.intel.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	sarah.a.sharp@...ux.intel.com, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, jianqian <jianqiang.tang@...el.com>
Subject: Re: [RFC/PATCH] usb/xhci: avoid kernel panic on xhci_suspend()

On Wed, Jan 08, 2014 at 10:48:06AM -0500, Alan Stern wrote:
> On Tue, 7 Jan 2014, Greg KH wrote:
> 
> > On Tue, Jan 07, 2014 at 05:44:26PM -0800, David Cohen wrote:
> > > From: jianqian <jianqiang.tang@...el.com>
> > > 
> > > There is a possible kernel panic faced on xhci_suspend().
> > > Due to kernel modified the hub autosupend_delay to 0s, after usb1 root
> > > hub finishes initialization, it will trigger runtime_suspend and then
> > > it will trigger xhci runtime suspend. But at that time, if
> > > xhci->shared_hcd is still doing initialization, it is possible to face
> > > null pointer kernel panic in xhci_suspend() function.
> > > 
> > > This patch checks if xhci->shared_hcd is null to avoid panic.
> > 
> > That sounds like this is a race that should be fixed properly, not just
> > papered over, right?
> 
> That was my reaction too.  The best way to solve the problem is to 
> prevent the USB-2 root hub from suspending until after the USB-3 root 
> hub has been registered.

That makes sense. Thanks for the feedback.
I'll check for a new approach.

Br, David Cohen

> 
> Alan Stern
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