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Date: Tue, 4 Mar 2014 09:35:02 -0800
From: David Cohen <david.a.cohen@linux.intel.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Mathias Nyman <mathias.nyman@linux.intel.com>, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org, sarah.a.sharp@linux.intel.com,
        dan.j.williams@intel.com, stable@vger.kernel.org
Subject: Re: [PATCH v3 1/1] xhci: Prevent runtime pm from autosuspending
 during initialization
Message-ID: <20140304173502.GA22202@psi-dev26.jf.intel.com>
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Hi Greg,

On Tue, Mar 04, 2014 at 09:04:58AM -0800, Greg KH wrote:
> On Tue, Mar 04, 2014 at 01:50:55PM +0200, Mathias Nyman wrote:
> > On 03/03/2014 08:37 PM, Greg KH wrote:
> > >On Mon, Mar 03, 2014 at 07:30:17PM +0200, Mathias Nyman wrote:
> > >>xHCI driver has its own pci probe function that will call usb_hcd_pci_probe
> > >>to register its usb-2 bus, and then continue to manually register the
> > >>usb-3 bus. usb_hcd_pci_probe does a pm_runtime_put_noidle at the end and
> > >>might thus trigger a runtime suspend before the usb-3 bus is ready.
> > >
> > >What is the result if that happens?
> > 
> > Crashes. Null pointer dereference in xhci_suspend() when touching
> > xhci->shared_hcd before it's initialized. More info here:
> > 
> > http://marc.info/?l=linux-usb&m=138914518219334&w=2
> > 
> > >
> > >Is this a regression from 3.13?  Or something new for 3.14?
> > >
> > 
> > According to reporter its been around since 3.7
> > 
> > commit 596d789a211d134dc5f94d1e5957248c204ef850
> > USB: set hub's default autosuspend delay as 0
> > 
> > But nobody else than the reporter is able to trigger it.
> 
> Then it can wait for 3.15-rc1, and then go back to the stable trees at
> that time, right?  I'd prefer that as it's not a regression and not
> common.
> 
> > >What platform(s) are affected by this?
> > 
> > David, the reporter (added to cc), mentioned
> > "This bug happened in a platform with 1 usb3 host controller + 1 usb3 OTG
> > controller" run by some Intel internal group
> > 
> > http://marc.info/?l=linux-usb&m=138915969822029&w=2
> 
> That sounds like a "not shipping platform" to me :)

Not quite. You'd find this configuration on Asus T100T. I said "not
quite" because I don't think we can run Linux smoothly on it yet. But...

> 
> Please resend this with patches for 3.15-rc1.

...that sounds fine :)

Br, David

> 
> thanks,
> 
> greg k-h