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SubjectRe: [ 02/38] PCI/PM: Fix deadlock when unbinding device if parent in D3cold
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@intel.com>
> > >
> > > 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@intel.com>
> > 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?

thanks,

greg k-h


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