linux-kernel - Re: [PATCH v3 1/1] xhci: Prevent runtime pm from autosuspending during initialization

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Date:	Tue, 04 Mar 2014 13:50:55 +0200
From:	Mathias Nyman <mathias.nyman@...ux.intel.com>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	sarah.a.sharp@...ux.intel.com, dan.j.williams@...el.com,
	stable@...r.kernel.org, David Cohen <david.a.cohen@...ux.intel.com>
Subject: Re: [PATCH v3 1/1] xhci: Prevent runtime pm from autosuspending during
 initialization

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.

> 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

David, can you elaborate on the platform?

>> xhci-platform driver is not using usb_hcd_pci_probe to set up
>> busses and should not need to have it's usage count increased during probe.
>
> I didn't think we had any in-kernel users of the xhci-platform driver,
> has that changed and I missed a new platform being added?
>

Not that I'm aware of. I just wanted to point out that this issue is 
only a matter on pci enumerated xhci hosts.

-Mathias

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