[PATCH] PCI: hotplug: Allow marking devices as disconnected during bind/unbind

[Lukas Wunner <lukas@wunner.de>]

On surprise removal, pciehp_unconfigure_device() and acpiphp's
trim_stale_devices() call pci_dev_set_disconnected() to mark removed
devices as permanently offline.  Thereby, the PCI core and drivers know
to skip device accesses.

However pci_dev_set_disconnected() takes the device_lock and thus waits
for a concurrent driver bind or unbind to complete.  As a result, the
driver's ->probe and ->remove hooks have no chance to learn that the
device is gone.

That doesn't make any sense, so drop the device_lock and instead use
atomic xchg() and cmpxchg() operations to update the device state.

As a byproduct, an AB-BA deadlock reported by Anatoli is fixed which
occurs on surprise removal with AER concurrently performing a bus reset.

AER bus reset:

  INFO: task irq/26-aerdrv:95 blocked for more than 120 seconds.
  Tainted: G        W          6.2.0-rc3-custom-norework-jan11+
  schedule
  rwsem_down_write_slowpath
  down_write_nested
  pciehp_reset_slot                      # acquires reset_lock
  pci_reset_hotplug_slot
  pci_slot_reset                         # acquires device_lock
  pci_bus_error_reset
  aer_root_reset
  pcie_do_recovery
  aer_process_err_devices
  aer_isr

pciehp surprise removal:

  INFO: task irq/26-pciehp:96 blocked for more than 120 seconds.
  Tainted: G        W          6.2.0-rc3-custom-norework-jan11+
  schedule_preempt_disabled
  __mutex_lock
  mutex_lock_nested
  pci_dev_set_disconnected               # acquires device_lock
  pci_walk_bus
  pciehp_unconfigure_device
  pciehp_disable_slot
  pciehp_handle_presence_or_link_change
  pciehp_ist                             # acquires reset_lock

Fixes: a6bd101b8f84 ("PCI: Unify device inaccessible")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=215590
Reported-by: Anatoli Antonovitch <anatoli.antonovitch@amd.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: stable@vger.kernel.org # v4.20+
Cc: Keith Busch <kbusch@kernel.org>
---
 drivers/pci/pci.h | 43 +++++++++++++------------------------------
 1 file changed, 13 insertions(+), 30 deletions(-)

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 9ed3b55..5d5a44a 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -310,53 +310,36 @@ struct pci_sriov {
  * @dev: PCI device to set new error_state
  * @new: the state we want dev to be in
  *
- * Must be called with device_lock held.
+ * If the device is experiencing perm_failure, it has to remain in that state.
+ * Any other transition is allowed.
  *
  * Returns true if state has been changed to the requested state.
  */
 static inline bool pci_dev_set_io_state(struct pci_dev *dev,
 					pci_channel_state_t new)
 {
-	bool changed = false;
+	pci_channel_state_t old;
 
-	device_lock_assert(&dev->dev);
 	switch (new) {
 	case pci_channel_io_perm_failure:
-		switch (dev->error_state) {
-		case pci_channel_io_frozen:
-		case pci_channel_io_normal:
-		case pci_channel_io_perm_failure:
-			changed = true;
-			break;
-		}
-		break;
+		xchg(&dev->error_state, pci_channel_io_perm_failure);
+		return true;
 	case pci_channel_io_frozen:
-		switch (dev->error_state) {
-		case pci_channel_io_frozen:
-		case pci_channel_io_normal:
-			changed = true;
-			break;
-		}
-		break;
+		old = cmpxchg(&dev->error_state, pci_channel_io_normal,
+			      pci_channel_io_frozen);
+		return old != pci_channel_io_perm_failure;
 	case pci_channel_io_normal:
-		switch (dev->error_state) {
-		case pci_channel_io_frozen:
-		case pci_channel_io_normal:
-			changed = true;
-			break;
-		}
-		break;
+		old = cmpxchg(&dev->error_state, pci_channel_io_frozen,
+			      pci_channel_io_normal);
+		return old != pci_channel_io_perm_failure;
+	default:
+		return false;
 	}
-	if (changed)
-		dev->error_state = new;
-	return changed;
 }
 
 static inline int pci_dev_set_disconnected(struct pci_dev *dev, void *unused)
 {
-	device_lock(&dev->dev);
 	pci_dev_set_io_state(dev, pci_channel_io_perm_failure);
-	device_unlock(&dev->dev);
 
 	return 0;
 }
-- 
2.39.1