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Subject[PATCH 5.2 073/137] powerpc/eeh: Clean up EEH PEs after recovery finishes
Date
From: Oliver O'Halloran <oohall@gmail.com>

[ Upstream commit 799abe283e5103d48e079149579b4f167c95ea0e ]

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since the eeh_pe pointer in the eeh_event structure is no
longer valid.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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/kernel/eeh_driver.c | 36 ++++++++++++++++++++++++++++++--
arch/powerpc/kernel/eeh_event.c | 8 +++++++
arch/powerpc/kernel/eeh_pe.c | 23 +++++++++++++++++++-
3 files changed, 64 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/eeh_driver.c b/arch/powerpc/kernel/eeh_driver.c
index 1fbe541856f5e..fe0c32fb9f96f 100644
--- a/arch/powerpc/kernel/eeh_driver.c
+++ b/arch/powerpc/kernel/eeh_driver.c
@@ -744,6 +744,33 @@ static int eeh_reset_device(struct eeh_pe *pe, struct pci_bus *bus,
*/
#define MAX_WAIT_FOR_RECOVERY 300

+
+/* Walks the PE tree after processing an event to remove any stale PEs.
+ *
+ * NB: This needs to be recursive to ensure the leaf PEs get removed
+ * before their parents do. Although this is possible to do recursively
+ * we don't since this is easier to read and we need to garantee
+ * the leaf nodes will be handled first.
+ */
+static void eeh_pe_cleanup(struct eeh_pe *pe)
+{
+ struct eeh_pe *child_pe, *tmp;
+
+ list_for_each_entry_safe(child_pe, tmp, &pe->child_list, child)
+ eeh_pe_cleanup(child_pe);
+
+ if (pe->state & EEH_PE_KEEP)
+ return;
+
+ if (!(pe->state & EEH_PE_INVALID))
+ return;
+
+ if (list_empty(&pe->edevs) && list_empty(&pe->child_list)) {
+ list_del(&pe->child);
+ kfree(pe);
+ }
+}
+
/**
* eeh_handle_normal_event - Handle EEH events on a specific PE
* @pe: EEH PE - which should not be used after we return, as it may
@@ -782,8 +809,6 @@ void eeh_handle_normal_event(struct eeh_pe *pe)
return;
}

- eeh_pe_state_mark(pe, EEH_PE_RECOVERING);
-
eeh_pe_update_time_stamp(pe);
pe->freeze_count++;
if (pe->freeze_count > eeh_max_freezes) {
@@ -973,6 +998,12 @@ void eeh_handle_normal_event(struct eeh_pe *pe)
return;
}
}
+
+ /*
+ * Clean up any PEs without devices. While marked as EEH_PE_RECOVERYING
+ * we don't want to modify the PE tree structure so we do it here.
+ */
+ eeh_pe_cleanup(pe);
eeh_pe_state_clear(pe, EEH_PE_RECOVERING, true);
}

@@ -1045,6 +1076,7 @@ void eeh_handle_special_event(void)
*/
if (rc == EEH_NEXT_ERR_FROZEN_PE ||
rc == EEH_NEXT_ERR_FENCED_PHB) {
+ eeh_pe_state_mark(pe, EEH_PE_RECOVERING);
eeh_handle_normal_event(pe);
} else {
pci_lock_rescan_remove();
diff --git a/arch/powerpc/kernel/eeh_event.c b/arch/powerpc/kernel/eeh_event.c
index 64cfbe41174b2..e36653e5f76b3 100644
--- a/arch/powerpc/kernel/eeh_event.c
+++ b/arch/powerpc/kernel/eeh_event.c
@@ -121,6 +121,14 @@ int __eeh_send_failure_event(struct eeh_pe *pe)
}
event->pe = pe;

+ /*
+ * Mark the PE as recovering before inserting it in the queue.
+ * This prevents the PE from being free()ed by a hotplug driver
+ * while the PE is sitting in the event queue.
+ */
+ if (pe)
+ eeh_pe_state_mark(pe, EEH_PE_RECOVERING);
+
/* We may or may not be called in an interrupt context */
spin_lock_irqsave(&eeh_eventlist_lock, flags);
list_add(&event->list, &eeh_eventlist);
diff --git a/arch/powerpc/kernel/eeh_pe.c b/arch/powerpc/kernel/eeh_pe.c
index 854cef7b18f4d..f0813d50e0b1c 100644
--- a/arch/powerpc/kernel/eeh_pe.c
+++ b/arch/powerpc/kernel/eeh_pe.c
@@ -491,6 +491,7 @@ 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;
struct pci_dn *pdn = eeh_dev_to_pdn(edev);

@@ -516,10 +517,21 @@ 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);
@@ -528,6 +540,15 @@ 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) {
--
2.20.1


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