powerpc/eeh: Clean up EEH PEs after recovery finishes

When the last device in an eeh_pe is removed the eeh_pe structure itself
(and any empty parents) are freed since they are no longer needed. This
results in a crash when a hotplug driver is involved since the following
may occur:

1. Device is suprise removed.
2. Driver performs an MMIO, which fails and queues and eeh_event.
3. Hotplug driver receives a hotplug interrupt and removes any
   pci_devs that were under the slot.
4. pci_dev is torn down and the eeh_pe is freed.
5. The EEH event handler thread processes the eeh_event and crashes
   since the eeh_pe pointer in the eeh_event structure is no
   longer valid.

Crashing is generally considered poor form. Instead of doing that use
the fact PEs are marked as EEH_PE_INVALID to keep them around until the
end of the recovery cycle, at which point we can safely prune any empty
PEs.

Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190903101605.2890-2-oohall@gmail.com

1 files changed, 22 insertions, 1 deletions

diff --git a/arch/powerpc/kernel/eeh_pe.c b/arch/powerpc/kernel/eeh_pe.c
index 1a6254bcf056..177852e39a25 100644
--- a/arch/powerpc/kernel/eeh_pe.c
+++ b/arch/powerpc/kernel/eeh_pe.c
@@ -470,6 +470,7 @@ int eeh_add_to_parent_pe(struct eeh_dev *edev)
 int eeh_rmv_from_parent_pe(struct eeh_dev *edev)
 {
 	struct eeh_pe *pe, *parent, *child;
+	bool keep, recover;
 	int cnt;
 
 	pe = eeh_dev_to_pe(edev);
@@ -490,10 +491,21 @@ int eeh_rmv_from_parent_pe(struct eeh_dev *edev)
 	 */
 	while (1) {
 		parent = pe->parent;
+
+		/* PHB PEs should never be removed */
 		if (pe->type & EEH_PE_PHB)
 			break;
 
-		if (!(pe->state & EEH_PE_KEEP)) {
+		/*
+		 * XXX: KEEP is set while resetting a PE. I don't think it's
+		 * ever set without RECOVERING also being set. I could
+		 * be wrong though so catch that with a WARN.
+		 */
+		keep = !!(pe->state & EEH_PE_KEEP);
+		recover = !!(pe->state & EEH_PE_RECOVERING);
+		WARN_ON(keep && !recover);
+
+		if (!keep && !recover) {
 			if (list_empty(&pe->edevs) &&
 			    list_empty(&pe->child_list)) {
 				list_del(&pe->child);
@@ -502,6 +514,15 @@ int eeh_rmv_from_parent_pe(struct eeh_dev *edev)
 				break;
 			}
 		} else {
+			/*
+			 * Mark the PE as invalid. At the end of the recovery
+			 * process any invalid PEs will be garbage collected.
+			 *
+			 * We need to delay the free()ing of them since we can
+			 * remove edev's while traversing the PE tree which
+			 * might trigger the removal of a PE and we can't
+			 * deal with that (yet).
+			 */
 			if (list_empty(&pe->edevs)) {
 				cnt = 0;
 				list_for_each_entry(child, &pe->child_list, child) {