[PATCHv2] pci: make reset_subordinate hotplug safe

[Keith Busch <kbusch@meta.com>]

From: Keith Busch <kbusch@kernel.org>

Use the slot reset method when restting 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 could be done like this:

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

Prior to this patch, an example kernel dmesg may show a message 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>
---
v1 -> v2:

  Added static declaration to local function, fixing compiler warning.

  Added more context in the change log with expected kernel messages
  before and after this patch.

 drivers/pci/pci-sysfs.c |  3 +--
 drivers/pci/pci.c       | 29 ++++++++++++++++++++++++++++-
 drivers/pci/pci.h       |  2 +-
 3 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 3881359440b1a..5c7c6f0c435f3 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_reset_bridge(pdev);
 
 		if (ret)
 			return ret;
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b14dd064006cc..72d88ea95f3cc 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5727,7 +5727,7 @@ EXPORT_SYMBOL_GPL(pci_probe_reset_bus);
  *
  * Same as above except return -EAGAIN if the bus cannot be locked
  */
-int __pci_reset_bus(struct pci_bus *bus)
+static int __pci_reset_bus(struct pci_bus *bus)
 {
 	int rc;
 
@@ -5747,6 +5747,33 @@ int __pci_reset_bus(struct pci_bus *bus)
 	return rc;
 }
 
+int pci_reset_bridge(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_reset_slot(slot))
+			goto bus_reset;
+
+	mutex_unlock(&pci_slot_mutex);
+	return 0;
+bus_reset:
+	mutex_unlock(&pci_slot_mutex);
+	return __pci_reset_bus(bus);
+}
+
 /**
  * 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 36f8c0985430a..f216e7a37d726 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_reset_bridge(struct pci_dev *dev);
 
 struct pci_cap_saved_data {
 	u16		cap_nr;
-- 
2.47.3