From: Yicong Yang <yangyicong@hisilicon.com>
Date: Mon, 4 Apr 2022 14:25:39 +0800
Subject: PCI: Avoid pci_dev_lock() AB/BA deadlock with sriov_numvfs_store()
Git-commit: a91ee0e9fca9d7501286cfbced9b30a33e52740a
Patch-mainline: 5.19-rc1
References: git-fixes

The sysfs sriov_numvfs_store() path acquires the device lock before the
config space access lock:

  sriov_numvfs_store
    device_lock                 # A (1) acquire device lock
    sriov_configure
      vfio_pci_sriov_configure  # (for example)
        vfio_pci_core_sriov_configure
          pci_disable_sriov
            sriov_disable
              pci_cfg_access_lock
                pci_wait_cfg    # B (4) wait for dev->block_cfg_access == 0

Previously, pci_dev_lock() acquired the config space access lock before the
device lock:

  pci_dev_lock
    pci_cfg_access_lock
      dev->block_cfg_access = 1 # B (2) set dev->block_cfg_access = 1
    device_lock                 # A (3) wait for device lock

Any path that uses pci_dev_lock(), e.g., pci_reset_function(), may
deadlock with sriov_numvfs_store() if the operations occur in the sequence
(1) (2) (3) (4).

Avoid the deadlock by reversing the order in pci_dev_lock() so it acquires
the device lock before the config space access lock, the same as the
sriov_numvfs_store() path.

[bhelgaas: combined and adapted commit log from Jay Zhou's independent
subsequent posting:
https://lore.kernel.org/r/20220404062539.1710-1-jianjay.zhou@huawei.com]
Link: https://lore.kernel.org/linux-pci/1583489997-17156-1-git-send-email-yangyicong@hisilicon.com/
Also-posted-by: Jay Zhou <jianjay.zhou@huawei.com>
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 drivers/pci/pci.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5063,18 +5063,18 @@ static int pci_reset_bus_function(struct
 
 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 */
 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;
@@ -5083,8 +5083,8 @@ EXPORT_SYMBOL_GPL(pci_dev_trylock);
 
 void pci_dev_unlock(struct pci_dev *dev)
 {
-	device_unlock(&dev->dev);
 	pci_cfg_access_unlock(dev);
+	device_unlock(&dev->dev);
 }
 EXPORT_SYMBOL_GPL(pci_dev_unlock);