PCI: Fix driver_managed_dma check

JIRA: https://issues.redhat.com/browse/RHEL-116573

Upstream Status: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

commit 78447d4
Author: Robin Murphy <robin.murphy@arm.com>
Date:   Fri Apr 25 14:39:29 2025 +0100

    PCI: Fix driver_managed_dma check

    Since it's not currently safe to take device_lock() in the IOMMU probe
    path, that can race against really_probe() setting dev->driver before
    attempting to bind. The race itself isn't so bad, since we're only
    concerned with dereferencing dev->driver itself anyway, but sadly my
    attempt to implement the check with minimal churn leads to a kind of
    Time-of-Check to Time-of-Use (TOCTOU) issue, where dev->driver becomes
    valid after to_pci_driver(NULL) is already computed, and thus the check
    fails to work as intended.

    Will and I both hit this with the platform bus, but the pattern here is
    the same, so fix it for correctness too.

    Fixes: bcb81ac ("iommu: Get DT/ACPI parsing into the proper probe path")
    Reported-by: Will McVicker <willmcvicker@google.com>
    Signed-off-by: Robin Murphy <robin.murphy@arm.com>
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
    Reviewed-by: Will McVicker <willmcvicker@google.com>
    Link: https://patch.msgid.link/20250425133929.646493-4-robin.murphy@arm.com

Signed-off-by: Eder Zulian <ezulian@redhat.com>

Author: efzrh

drivers/pci/pci-driver.c

@@ -1641,7 +1641,7 @@ static int pci_bus_num_vf(struct device *dev)
  */
 static int pci_dma_configure(struct device *dev)
 {
-	struct pci_driver *driver = to_pci_driver(dev->driver);
+	const struct device_driver *drv = READ_ONCE(dev->driver);
 	struct device *bridge;
 	int ret = 0;
 
@@ -1658,8 +1658,8 @@ static int pci_dma_configure(struct device *dev)
 
 	pci_put_host_bridge_device(bridge);
 
-	/* @driver may not be valid when we're called from the IOMMU layer */
-	if (!ret && dev->driver && !driver->driver_managed_dma) {
+	/* @drv may not be valid when we're called from the IOMMU layer */
+	if (!ret && drv && !to_pci_driver(drv)->driver_managed_dma) {
 		ret = iommu_device_use_default_domain(dev);
 		if (ret)
 			arch_teardown_dma_ops(dev);