Re: [ 02/38] PCI/PM: Fix deadlock when unbinding device if parent inD3cold

[Greg Kroah-Hartman]

On Mon, Nov 26, 2012 at 10:55:05AM -0800, Greg Kroah-Hartman wrote:
> On Fri, Nov 23, 2012 at 11:09:37AM +0800, Huang Ying wrote:
> > On Fri, 2012-11-23 at 02:35 +0000, Ben Hutchings wrote:
> > > On Wed, 2012-11-21 at 16:39 -0800, Greg Kroah-Hartman wrote:
> > > > 3.0-stable review patch.  If anyone has any objections, please let me know.
> > > > 
> > > > ------------------
> > > > 
> > > > From: Huang Ying <ying.huang@xxxxxxxxx>
> > > > 
> > > > commit 90b5c1d7c45eeb622302680ff96ed30c1a2b6f0e upstream.
> > > > 
> > > > If a PCI device and its parents are put into D3cold, unbinding the
> > > > device will trigger deadlock as follow:
> > > > 
> > > > - driver_unbind
> > > >   - device_release_driver
> > > >     - device_lock(dev)				<--- previous lock here
> > > >     - __device_release_driver
> > > >       - pm_runtime_get_sync
> > > >         ...
> > > >           - rpm_resume(dev)
> > > >             - rpm_resume(dev->parent)
> > > >               ...
> > > >                 - pci_pm_runtime_resume
> > > >                   ...
> > > >                   - pci_set_power_state
> > > >                     - __pci_start_power_transition
> > > >                       - pci_wakeup_bus(dev->parent->subordinate)
> > > >                         - pci_walk_bus
> > > >                           - device_lock(dev)	<--- deadlock here
> > > > 
> > > > 
> > > > If we do not do device_lock in pci_walk_bus, we can avoid deadlock.
> > > > Device_lock in pci_walk_bus is introduced in commit:
> > > > d71374dafbba7ec3f67371d3b7e9f6310a588808, corresponding email thread
> > > > is: https://lkml.org/lkml/2006/5/26/38.  The patch author Zhang Yanmin
> > > > said device_lock is added to pci_walk_bus because:
> > > > 
> > > >   Some error handling functions call pci_walk_bus. For example, PCIe
> > > >   aer. Here we lock the device, so the driver wouldn't detach from the
> > > >   device, as the cb might call driver's callback function.
> > > > 
> > > > So I fixed the deadlock as follows:
> > > > 
> > > > - remove device_lock from pci_walk_bus
> > > > - add device_lock into callback if callback will call driver's callback
> > > > 
> > > > I checked pci_walk_bus users one by one, and found only PCIe aer needs
> > > > device lock.
> > > [...]
> > > 
> > > What about eeh_report_error() in
> > > arch/powerpc/platforms/pseries/eeh_driver.c?
> > 
> > En...  Because pci_walk_bus() invocation is removed in 3.7, so this
> > patch is only valid for 3.7.  We need another version for 3.6.
> > 
> > > Also, is the deadlock even possible before this change in Linux 3.6?
> > > 
> > > commit 448bd857d48e69b33ef323739dc6d8ca20d4cda7
> > > Author: Huang Ying <ying.huang@xxxxxxxxx>
> > > Date:   Sat Jun 23 10:23:51 2012 +0800
> > > 
> > >     PCI/PM: add PCIe runtime D3cold support
> > 
> > Before this, there will be no deadlock.  So we do not need fixes before
> > Linux 3.6.
> 
> So the first patch mentioned here should not be included in the 3.0 and
> 3.4 stable kernel releases?

Ok, I've dropped the patch from 3.0 and 3.4-stable trees now.

For 3.6, what should I do?

thanks,

greg k-h
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