[PATCH v15 2/5] PCI: Fix AB-BA deadlock between device_lock and pci_rescan_remove_lock in remove_store

[Benjamin Block <bblock@linux.ibm.com>]

From: Ionut Nechita <ionut.nechita@windriver.com>

remove_store() calls pci_stop_and_remove_bus_device_locked() which
takes pci_rescan_remove_lock first, then device_lock during driver
release.  Meanwhile, unbind_store() takes device_lock first (via
device_driver_detach), and the driver's .remove() callback may call
pci_disable_sriov() -> sriov_del_vfs() -> pci_lock_rescan_remove().

This creates an AB-BA deadlock:

  CPU0 (remove_store)               CPU1 (unbind_store)
  --------------------              --------------------
  pci_lock_rescan_remove()
                                    device_lock()
                                    driver .remove()
                                      sriov_del_vfs()
                                        pci_lock_rescan_remove()  <-- WAITS
  pci_stop_bus_device()
    device_release_driver()
      device_lock()                                               <-- WAITS

Fix this by first marking the device as dead using kill_device() to
prevent any new driver from binding, then calling device_release_driver()
before pci_stop_and_remove_bus_device_locked().

Marking the device dead closes the race window between unbinding and
removal where a new driver could theoretically bind: once the dead flag
is set, the device core will refuse any new driver probe.

After device_release_driver() returns, the driver is already unbound,
so the subsequent device_release_driver() call inside
pci_stop_and_remove_bus_device_locked() becomes a no-op.

Fixes: a5338e365c45 ("PCI/IOV: Fix race between SR-IOV enable/disable and hotplug")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Closes: https://lore.kernel.org/linux-pci/0ca9e675-478c-411d-be32-e2d81439288f@roeck-us.net/
Reported-by: Benjamin Block <bblock@linux.ibm.com>
Closes: https://lore.kernel.org/linux-pci/20260317090149.GA3835708@chlorum.ategam.org/
Suggested-by: Benjamin Block <bblock@linux.ibm.com>
Cc: stable@vger.kernel.org
Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Tested-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Ionut Nechita <ionut.nechita@windriver.com>
Signed-off-by: Benjamin Block <bblock@linux.ibm.com>
---
 drivers/pci/pci-sysfs.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 1f21856aac8a..b2f3e052d903 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -520,8 +520,36 @@ static ssize_t remove_store(struct device *dev, struct device_attribute *attr,
 	if (kstrtoul(buf, 0, &val) < 0)
 		return -EINVAL;
 
-	if (val && device_remove_file_self(dev, attr))
+	if (val && device_remove_file_self(dev, attr)) {
+		/*
+		 * Mark the device as dead so that no new driver can bind
+		 * between the unbind and the removal below.  Once the
+		 * dead flag is set, the device core will refuse any new
+		 * driver probe.
+		 */
+		device_lock(dev);
+		kill_device(dev);
+		device_unlock(dev);
+
+		/*
+		 * Unbind the driver before removing the device to avoid
+		 * an AB-BA deadlock between device_lock and
+		 * pci_rescan_remove_lock.  Without this, remove_store
+		 * takes pci_rescan_remove_lock first (via
+		 * pci_stop_and_remove_bus_device_locked) and then
+		 * device_lock during driver release, while a concurrent
+		 * unbind_store (or sriov_numvfs_store) takes device_lock
+		 * first and then pci_rescan_remove_lock (via
+		 * sriov_del_vfs), creating a circular dependency.
+		 *
+		 * By unbinding first, the driver's .remove() callback
+		 * (including any SR-IOV VF cleanup) completes before
+		 * pci_rescan_remove_lock is acquired, ensuring both
+		 * paths take locks in the same order.
+		 */
+		device_release_driver(dev);
 		pci_stop_and_remove_bus_device_locked(to_pci_dev(dev));
+	}
 	return count;
 }
 static DEVICE_ATTR_IGNORE_LOCKDEP(remove, 0220, NULL,
-- 
2.55.0