Re: [ 02/38] PCI/PM: Fix deadlock when unbinding device if parentin D3cold

[Huang Ying]

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.

Best Regards,
Huang Ying


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