[PATCH AUTOSEL 6.19-5.10] PCI: Fix pci_slot_lock () device locking

[Sasha Levin <sashal@kernel.org>]

From: Keith Busch <kbusch@kernel.org>

[ Upstream commit 1f5e57c622b4dc9b8e7d291d560138d92cfbe5bf ]

Like pci_bus_lock(), pci_slot_lock() needs to lock the bridge device to
prevent warnings like:

  pcieport 0000:e2:05.0: unlocked secondary bus reset via: pciehp_reset_slot+0x55/0xa0

Take and release the lock for the bridge providing the slot for the
lock/trylock and unlock routines.

Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Link: https://patch.msgid.link/20260130165953.751063-3-kbusch@meta.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

The commit is not yet in this tree. That's fine - it's a candidate being
evaluated.

### SUMMARY

**What the commit fixes**: `pci_slot_lock()`, `pci_slot_unlock()`, and
`pci_slot_trylock()` don't lock the bridge device providing the slot,
unlike their `pci_bus_*()` counterparts which were fixed in v6.11
(commit `a4e772898f8bf`). This causes:
1. Warnings about "unlocked secondary bus reset" during PCIe hotplug
   slot reset
2. A real synchronization gap - the bridge device can be accessed
   concurrently during slot reset operations

**Why it matters for stable**:
- Fixes a real locking bug that triggers warnings and could lead to
  races during PCI hotplug operations
- PCIe hotplug is widely used (servers, Thunderbolt, NVMe)
- The fix follows an established, proven pattern (mirrors what
  `pci_bus_lock()` already does)
- Small, surgical change (~20 lines of logic in one file)
- Written by Keith Busch (PCI/NVMe expert), committed by Bjorn Helgaas
  (PCI maintainer), reviewed by Dan Williams
- No new features, no API changes

**Dependencies**: Requires commit `a4e772898f8bf` ("PCI: Add missing
bridge lock to pci_bus_lock()") which is in v6.11+. May also depend on
`f3efb9569b4a2` ("PCI: Fix lock symmetry in pci_slot_unlock()") from
v6.16-rc1. The backport would need to target only stable trees that
contain the prerequisite.

**Risk**: Very low. The change adds symmetric lock/unlock operations
following an identical pattern already proven in `pci_bus_lock()`. The
trylock path correctly handles contention (unlocks bridge on failure).

This is a clear bug fix - missing synchronization during PCI slot reset
operations - that is small, well-reviewed, follows a proven pattern, and
fixes a real locking issue. It meets all stable kernel criteria.

**YES**

 drivers/pci/pci.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 13dbb405dc31f..b99ad5f50f30d 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5290,10 +5290,9 @@ static int pci_bus_trylock(struct pci_bus *bus)
 /* Do any devices on or below this slot prevent a bus reset? */
 static bool pci_slot_resettable(struct pci_slot *slot)
 {
-	struct pci_dev *dev;
+	struct pci_dev *dev, *bridge = slot->bus->self;
 
-	if (slot->bus->self &&
-	    (slot->bus->self->dev_flags & PCI_DEV_FLAGS_NO_BUS_RESET))
+	if (bridge && (bridge->dev_flags & PCI_DEV_FLAGS_NO_BUS_RESET))
 		return false;
 
 	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
@@ -5310,7 +5309,10 @@ static bool pci_slot_resettable(struct pci_slot *slot)
 /* Lock devices from the top of the tree down */
 static void pci_slot_lock(struct pci_slot *slot)
 {
-	struct pci_dev *dev;
+	struct pci_dev *dev, *bridge = slot->bus->self;
+
+	if (bridge)
+		pci_dev_lock(bridge);
 
 	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
 		if (!dev->slot || dev->slot != slot)
@@ -5325,7 +5327,7 @@ static void pci_slot_lock(struct pci_slot *slot)
 /* Unlock devices from the bottom of the tree up */
 static void pci_slot_unlock(struct pci_slot *slot)
 {
-	struct pci_dev *dev;
+	struct pci_dev *dev, *bridge = slot->bus->self;
 
 	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
 		if (!dev->slot || dev->slot != slot)
@@ -5335,12 +5337,18 @@ static void pci_slot_unlock(struct pci_slot *slot)
 		else
 			pci_dev_unlock(dev);
 	}
+
+	if (bridge)
+		pci_dev_unlock(bridge);
 }
 
 /* Return 1 on successful lock, 0 on contention */
 static int pci_slot_trylock(struct pci_slot *slot)
 {
-	struct pci_dev *dev;
+	struct pci_dev *dev, *bridge = slot->bus->self;
+
+	if (bridge && !pci_dev_trylock(bridge))
+		return 0;
 
 	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
 		if (!dev->slot || dev->slot != slot)
@@ -5365,6 +5373,9 @@ static int pci_slot_trylock(struct pci_slot *slot)
 		else
 			pci_dev_unlock(dev);
 	}
+
+	if (bridge)
+		pci_dev_unlock(bridge);
 	return 0;
 }
 
-- 
2.51.0