[PATCHv3 4/4] pci: make reset_subordinate hotplug safe

[Keith Busch <kbusch@meta.com>]

From: Keith Busch <kbusch@kernel.org>

Use the slot reset method when resetting the bridge if the bus contains
hot plug slots. This fixes spurious hot plug events that are triggered
by the secondary bus reset that bypasses the slot's detection disabling.

Resetting a bridge's subordinate bus can be done like this:

  # echo 1 > /sys/bus/pci/devices/0000:50:01.0/reset_subordinate

Prior to this patch, an example kernel message may show something like:

  pcieport 0000:50:01.0: pciehp: Slot(40): Link Down

With this change, the pciehp driver ignores the link event during the
reset, so may show this message instead:

  pcieport 0000:50:01.0: pciehp: Slot(40): Link Down/Up ignored

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 drivers/pci/pci-sysfs.c |  3 +-
 drivers/pci/pci.c       | 71 ++++++++++++++++++++++++++++-------------
 drivers/pci/pci.h       |  2 +-
 3 files changed, 50 insertions(+), 26 deletions(-)

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index c2df915ad2d29..039d3dc157006 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -553,7 +553,6 @@ static ssize_t reset_subordinate_store(struct device *dev,
 				const char *buf, size_t count)
 {
 	struct pci_dev *pdev = to_pci_dev(dev);
-	struct pci_bus *bus = pdev->subordinate;
 	unsigned long val;
 
 	if (!capable(CAP_SYS_ADMIN))
@@ -563,7 +562,7 @@ static ssize_t reset_subordinate_store(struct device *dev,
 		return -EINVAL;
 
 	if (val) {
-		int ret = __pci_reset_bus(bus);
+		int ret = pci_try_reset_bridge(pdev);
 
 		if (ret)
 			return ret;
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index df9ed73dad416..27817c6603a5c 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -51,6 +51,10 @@ unsigned int pci_pm_d3hot_delay;
 
 static void pci_pme_list_scan(struct work_struct *work);
 
+#define PCI_SLOT_RESET_MASKED true
+#define PCI_SLOT_RESET_UNMASKED false
+static int pci_reset_bridge(struct pci_dev *bridge, bool save);
+
 static LIST_HEAD(pci_pme_list);
 static DEFINE_MUTEX(pci_pme_list_mutex);
 static DECLARE_DELAYED_WORK(pci_pme_work, pci_pme_list_scan);
@@ -5420,29 +5424,7 @@ static int pci_bus_reset(struct pci_bus *bus, bool probe)
  */
 int pci_bus_error_reset(struct pci_dev *bridge)
 {
-	struct pci_bus *bus = bridge->subordinate;
-	struct pci_slot *slot;
-
-	if (!bus)
-		return -ENOTTY;
-
-	mutex_lock(&pci_slot_mutex);
-	if (list_empty(&bus->slots))
-		goto bus_reset;
-
-	list_for_each_entry(slot, &bus->slots, list)
-		if (pci_probe_reset_slot(slot))
-			goto bus_reset;
-
-	list_for_each_entry(slot, &bus->slots, list)
-		if (pci_slot_reset(slot, PCI_RESET_DO_RESET))
-			goto bus_reset;
-
-	mutex_unlock(&pci_slot_mutex);
-	return 0;
-bus_reset:
-	mutex_unlock(&pci_slot_mutex);
-	return pci_bus_reset(bridge->subordinate, PCI_RESET_DO_RESET);
+	return pci_reset_bridge(bridge, PCI_SLOT_RESET_UNMASKED);
 }
 
 /**
@@ -5483,6 +5465,49 @@ static int pci_try_reset_bus(struct pci_bus *bus)
 	return rc;
 }
 
+static int pci_reset_bridge(struct pci_dev *bridge, bool masked)
+{
+	struct pci_bus *bus = bridge->subordinate;
+	struct pci_slot *slot;
+
+	if (!bus)
+		return -ENOTTY;
+
+	mutex_lock(&pci_slot_mutex);
+	if (list_empty(&bus->slots))
+		goto bus_reset;
+
+	list_for_each_entry(slot, &bus->slots, list)
+		if (pci_probe_reset_slot(slot))
+			goto bus_reset;
+
+	list_for_each_entry(slot, &bus->slots, list) {
+		int ret;
+
+		if (masked)
+			ret = pci_try_reset_slot(slot);
+		else
+			ret = pci_slot_reset(slot, PCI_RESET_DO_RESET);
+
+		if (ret)
+			goto bus_reset;
+	}
+
+	mutex_unlock(&pci_slot_mutex);
+	return 0;
+bus_reset:
+	mutex_unlock(&pci_slot_mutex);
+
+	if (masked)
+		return pci_try_reset_bus(bus);
+	return pci_bus_reset(bridge->subordinate, PCI_RESET_DO_RESET);
+}
+
+int pci_try_reset_bridge(struct pci_dev *bridge)
+{
+	return pci_reset_bridge(bridge, PCI_SLOT_RESET_MASKED);
+}
+
 /**
  * pci_reset_bus - Try to reset a PCI bus
  * @pdev: top level PCI device to reset via slot/bus
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 0e67014aa0013..790f2350b890c 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -197,7 +197,7 @@ bool pci_reset_supported(struct pci_dev *dev);
 void pci_init_reset_methods(struct pci_dev *dev);
 int pci_bridge_secondary_bus_reset(struct pci_dev *dev);
 int pci_bus_error_reset(struct pci_dev *dev);
-int __pci_reset_bus(struct pci_bus *bus);
+int pci_try_reset_bridge(struct pci_dev *dev);
 
 struct pci_cap_saved_data {
 	u16		cap_nr;
-- 
2.47.3