powerpc/eeh: Fix stale cached primary bus

powerpc/eeh: Fix stale cached primary bus

When PE is created, its primary bus is cached to pe->bus. At later
point, the cached primary bus is returned from eeh_pe_bus_get().
However, we could get stale cached primary bus and run into kernel
crash in one case: full hotplug as part of fenced PHB error recovery
releases all PCI busses under the PHB at unplugging time and recreate
them at plugging time. pe->bus is still dereferencing the PCI bus
that was released.

This adds another PE flag (EEH_PE_PRI_BUS) to represent the validity
of pe->bus. pe->bus is updated when its first child EEH device is
online and the flag is set. Before unplugging in full hotplug for
error recovery, the flag is cleared.

Fixes: 8cdb2833 ("powerpc/eeh: Trace PCI bus from PE")
Cc: [email protected] #v3.11+
Reported-by: Andrew Donnellan <[email protected]>
Reported-by: Pradipta Ghosh <[email protected]>
Signed-off-by: Gavin Shan <[email protected]>
Tested-by: Andrew Donnellan <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>