[PATCH 1/2] PCI: Change lock order in pci_dev_lock()

[PATCH 1/2] PCI: Change lock order in pci_dev_lock()

[Yicong Yang]

In pci_dev_lock(), we hold pci_lock for configuration access first,
then is device_lock. But in sriov enable routine, we hold device_lock
first and pci_lock subsequently. The inconsistent lock order  will have
potential deadlock problem.

In pci_dev_lock():
pci_dev_lock()
	pci_cfg_access_lock()
	device_lock()

When adding VF by sysfs:
sriov_numvfs_store()
	device_lock()
		...
		sriov_enable()
			pci_cfg_access_lock()

Adjust the lock order in pci_dev_lock(), pci_dev_trylock() and
pci_dev_unlock() to avoid potential deadlock condition.

Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
---
 drivers/pci/pci.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index e87196c..78c99ef 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4876,18 +4876,19 @@ static int pci_dev_reset_slot_function(struct pci_dev *dev, int probe)
 
 static void pci_dev_lock(struct pci_dev *dev)
 {
-	pci_cfg_access_lock(dev);
 	/* block PM suspend, driver probe, etc. */
 	device_lock(&dev->dev);
+
+	pci_cfg_access_lock(dev);
 }
 
 /* Return 1 on successful lock, 0 on contention */
 static int pci_dev_trylock(struct pci_dev *dev)
 {
-	if (pci_cfg_access_trylock(dev)) {
-		if (device_trylock(&dev->dev))
+	if (device_trylock(&dev->dev)) {
+		if (pci_cfg_access_trylock(dev))
 			return 1;
-		pci_cfg_access_unlock(dev);
+		device_unlock(&dev->dev);
 	}
 
 	return 0;
@@ -4895,8 +4896,8 @@ static int pci_dev_trylock(struct pci_dev *dev)
 
 static void pci_dev_unlock(struct pci_dev *dev)
 {
-	device_unlock(&dev->dev);
 	pci_cfg_access_unlock(dev);
+	device_unlock(&dev->dev);
 }
 
 static void pci_dev_save_and_disable(struct pci_dev *dev)
-- 
2.8.1