Re: [PATCHv2 16/20] PCI/pciehp: Implement error handling callbacks

[Keith Busch <keith.busch@intel.com>]

On Mon, Sep 10, 2018 at 06:09:26PM +0200, Lukas Wunner wrote:
> On Mon, Sep 10, 2018 at 08:56:42AM -0600, Keith Busch wrote:
> > The sysfs entries still function. Their actions are only temporarily
> > stalled during error handling. Once the slot reset is called, the
> > ctrl->pending_events is queried to take requested actions.
> 
> Okay I see.  Still, releasing the IRQ and requesting it again seems fairly
> heavy-wheight.  Why not just acquire ctrl->reset_lock?

That was looking like a nice way to handle it, but it introduces
circular locking between ctrl->reset_lock and pci_bus_sem:

CPU A                               CPU B
---------------------------------   ------------------------
pci_walk_bus                        pciehp_ist
 down_read(&pci_bus_sem)             down_read(&ctrl->reset_lock);
  pcie_portdrv_error_detected         pciehp_handle_presence_or_link_change
   pciehp_error_detected               pciehp_unconfigure_device
    down_write(&ctrl->reset_lock)       pci_stop_and_remove_bus_devicea
                                         down_write(&pci_bus_sem);