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Subject[PATCH] PCI: Fix "try" semantics of bus and slot reset
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Date
The commit referenced below introduced device locking around save and
restore of state for each device during a PCI bus "try" reset, making
it decidely non-"try" and prone to deadlock in the event that a device
is already locked. Restore __pci_reset_bus() and __pci_reset_slot()
to their advertised locking semantics by pushing the save and restore
functions into the branch where the entire tree is already locked.
Extend the helper function names with "_locked" and update the comment
to reflect this calling requirement.

Fixes: b014e96d1abb ("PCI: Protect pci_error_handlers->reset_notify() usage with device_lock()")
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
drivers/pci/pci.c | 53 ++++++++++++++++++++++++++---------------------------
1 file changed, 26 insertions(+), 27 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index c25acace7d91..870834cb6672 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5058,39 +5058,42 @@ static int pci_slot_trylock(struct pci_slot *slot)
return 0;
}

-/* Save and disable devices from the top of the tree down */
-static void pci_bus_save_and_disable(struct pci_bus *bus)
+/*
+ * Save and disable devices from the top of the tree down while holding
+ * the @dev mutex lock for the entire tree.
+ */
+static void pci_bus_save_and_disable_locked(struct pci_bus *bus)
{
struct pci_dev *dev;

list_for_each_entry(dev, &bus->devices, bus_list) {
- pci_dev_lock(dev);
pci_dev_save_and_disable(dev);
- pci_dev_unlock(dev);
if (dev->subordinate)
- pci_bus_save_and_disable(dev->subordinate);
+ pci_bus_save_and_disable_locked(dev->subordinate);
}
}

/*
- * Restore devices from top of the tree down - parent bridges need to be
- * restored before we can get to subordinate devices.
+ * Restore devices from top of the tree down while holding @dev mutex lock
+ * for the entire tree. Parent bridges need to be restored before we can
+ * get to subordinate devices.
*/
-static void pci_bus_restore(struct pci_bus *bus)
+static void pci_bus_restore_locked(struct pci_bus *bus)
{
struct pci_dev *dev;

list_for_each_entry(dev, &bus->devices, bus_list) {
- pci_dev_lock(dev);
pci_dev_restore(dev);
- pci_dev_unlock(dev);
if (dev->subordinate)
- pci_bus_restore(dev->subordinate);
+ pci_bus_restore_locked(dev->subordinate);
}
}

-/* Save and disable devices from the top of the tree down */
-static void pci_slot_save_and_disable(struct pci_slot *slot)
+/*
+ * Save and disable devices from the top of the tree down while holding
+ * the @dev mutex lock for the entire tree.
+ */
+static void pci_slot_save_and_disable_locked(struct pci_slot *slot)
{
struct pci_dev *dev;

@@ -5099,26 +5102,25 @@ static void pci_slot_save_and_disable(struct pci_slot *slot)
continue;
pci_dev_save_and_disable(dev);
if (dev->subordinate)
- pci_bus_save_and_disable(dev->subordinate);
+ pci_bus_save_and_disable_locked(dev->subordinate);
}
}

/*
- * Restore devices from top of the tree down - parent bridges need to be
- * restored before we can get to subordinate devices.
+ * Restore devices from top of the tree down while holding @dev mutex lock
+ * for the entire tree. Parent bridges need to be restored before we can
+ * get to subordinate devices.
*/
-static void pci_slot_restore(struct pci_slot *slot)
+static void pci_slot_restore_locked(struct pci_slot *slot)
{
struct pci_dev *dev;

list_for_each_entry(dev, &slot->bus->devices, bus_list) {
if (!dev->slot || dev->slot != slot)
continue;
- pci_dev_lock(dev);
pci_dev_restore(dev);
- pci_dev_unlock(dev);
if (dev->subordinate)
- pci_bus_restore(dev->subordinate);
+ pci_bus_restore_locked(dev->subordinate);
}
}

@@ -5177,16 +5179,15 @@ static int __pci_reset_slot(struct pci_slot *slot)
if (rc)
return rc;

- pci_slot_save_and_disable(slot);
-
if (pci_slot_trylock(slot)) {
+ pci_slot_save_and_disable_locked(slot);
might_sleep();
rc = pci_reset_hotplug_slot(slot->hotplug, 0);
+ pci_slot_restore_locked(slot);
pci_slot_unlock(slot);
} else
rc = -EAGAIN;

- pci_slot_restore(slot);

return rc;
}
@@ -5273,17 +5274,15 @@ static int __pci_reset_bus(struct pci_bus *bus)
if (rc)
return rc;

- pci_bus_save_and_disable(bus);
-
if (pci_bus_trylock(bus)) {
+ pci_bus_save_and_disable_locked(bus);
might_sleep();
rc = pci_bridge_secondary_bus_reset(bus->self);
+ pci_bus_restore_locked(bus);
pci_bus_unlock(bus);
} else
rc = -EAGAIN;

- pci_bus_restore(bus);
-
return rc;
}

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