powerpc/eeh: Fix invalid cached PE primary bus

BugLink: http://bugs.launchpad.net/bugs/1603449

The PE primary bus cannot be got from its child devices when having
full hotplug in error recovery. The PE primary bus is cached, which
is done in commit <05ba75f8> ("powerpc/eeh: Fix stale cached primary
bus"). In eeh_reset_device(), the flag (EEH_PE_PRI_BUS) is cleared
before the PCI hot remove. eeh_pe_bus_get() then returns NULL as the
PE primary bus in pnv_eeh_reset() and it crashes the kernel eventually.

This fixes the issue by clearing the flag (EEH_PE_PRI_BUS) before the
PCI hot add. With it, the PowerNV EEH reset backend (pnv_eeh_reset())
can get valid PE primary bus through eeh_pe_bus_get().

Fixes: 67086e32 ("powerpc/eeh: powerpc/eeh: Support error recovery for VF PE")
Reported-by: Pridhiviraj Paidipeddi <ppaiddipe@in.ibm.com>
Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
(backported from commit a3aa256b)
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

arch/powerpc/kernel/eeh_driver.c

@@ -583,7 +583,6 @@ static int eeh_reset_device(struct eeh_pe *pe, struct pci_bus *bus)
 	 */
 	eeh_pe_state_mark(pe, EEH_PE_KEEP);
 	if (bus) {
-		eeh_pe_state_clear(pe, EEH_PE_PRI_BUS);
 		pci_lock_rescan_remove();
 		pcibios_remove_pci_devices(bus);
 		pci_unlock_rescan_remove();
@@ -637,6 +636,7 @@ static int eeh_reset_device(struct eeh_pe *pe, struct pci_bus *bus)
 		ssleep(5);
 
 		eeh_pe_traverse(pe, eeh_pe_detach_dev, NULL);
+		eeh_pe_state_clear(pe, EEH_PE_PRI_BUS);
 		pcibios_add_pci_devices(frozen_bus);
 	}
 	eeh_pe_state_clear(pe, EEH_PE_KEEP);