[PATCH v4 3/3] s390/pci: Fix circular/recursive deadlocks in PCI-bus and -device release

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

When removing PCI device or PCI bus objects there are a couple of
call-chains where it is possible that the kernel runs into a circular
deadlock involving the central `pci_rescan_remove_lock`.

Two examples:

(A) Thread α receives a PCI event notifying the kernel that a PCI
virtual function has been moved into Reserved state, and so the PCI
subsystem will try to remove that PCI function. The call-chain for that
looks like this:
  __zpci_event_availability()
    -> zpci_zdev_put()              # will   lock(zpci_add_remove_lock),
                                    # and    lock(zpci_list_lock)
    -> zpci_release_device()        # will unlock(zpci_list_lock)
    -> zpci_cleanup_bus_resources() # will   lock(pci_rescan_remove_lock)

Thread β is triggered by userspace writing 0 into the SysFS attribute
`sriov_numvfs` of the parent PCI physical function of the same function
we just try to remove. This will also try to release the PCI virtual
function; but this time the call-chain looks like this:
  sriov_numvfs_store()
    -> ... (device driver dependent)
    -> sriov_disable()
    -> sriov_del_vfs()              # will   lock(pci_rescan_remove_lock)
    -> ... (deep chain)
    -> pci_release_dev()
    -> pcibios_release_device()
    -> zpci_zdev_put()              # will   lock(zpci_add_remove_lock)

If thread α and β coincide, this will result in a cyclic deadlock.

(B) Thread γ receives a PCI event notifying the kernel that one or more
PCI functions got hot plugged, and need to be configured. A possible
call-chain that might happen while the PCI subsystem is trying to add
those new function looks like this:
  __zpci_event_availability()
    -> ... (multiple ways in which a device gets added)
    -> zpci_add_device()            # will   lock(zpci_add_remove_lock)
    -> zpci_bus_device_register()
    -> zpci_bus_put()               # will   lock(zbus_list_lock)
    -> zpci_bus_release()           # will unlock(zbus_list_lock)
                                    # will   lock(pci_rescan_remove_lock)

Now the same thread β as above in (A) might coincide, and again could
result in a cyclic deadlock.

`pci_rescan_remove_lock` has to be and is taken at a "high level" in
most call-chains since it is intended to protect/mutual exclude all
rescan and/or removal actions taken in the PCI subsystem. So to prevent
the outlined deadlock scenarios above remove it instead from the "low
level" release functions for both the PCI device and PCI bus objects.

Instead, lock `pci_rescan_remove_lock` in all call-chains leading to
those release functions:
  * initialization of the PCI subsystem;
  * processing of availability events (CRWs) for PCI functions;
  * processing of error events (CRWs) for PCI functions;
  * architecture specific release PCI device implementation.

Additionally, remove `pci_rescan_remove_lock` from zpci_bus_scan_bus()
since its only caller zpci_scan_devices() is now always called with
`pci_rescan_remove_lock` already held.

Lastly, document the new locking expectations after these changes. Add
sparse and lockdep annotations to functions that previously locked
`pci_rescan_remove_lock` explicitly, making sure the lock is now
already held when called. Additionally also add the annotations to
zpci_zdev_put() and zpci_bus_put() to make sure that every function that
potentially drops the last reference already holds the lock to prevent
surprises.

Fixes: 05bc1be6db4b2 ("s390/pci: create zPCI bus")
Fixes: ab909509850b2 ("PCI: s390: Fix use-after-free of PCI resources with per-function hotplug")
Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Benjamin Block <bblock@linux.ibm.com>
---
 arch/s390/pci/pci.c       | 11 ++++++++---
 arch/s390/pci/pci_bus.c   | 15 ++++++++-------
 arch/s390/pci/pci_event.c | 28 +++++++++++++++++++---------
 arch/s390/pci/pci_iov.c   |  3 +--
 arch/s390/pci/pci_sysfs.c |  9 +++------
 5 files changed, 39 insertions(+), 27 deletions(-)

diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
index 2a430722cbe4..86ef1e516857 100644
--- a/arch/s390/pci/pci.c
+++ b/arch/s390/pci/pci.c
@@ -71,9 +71,11 @@ struct airq_iv *zpci_aif_sbv;
 EXPORT_SYMBOL_GPL(zpci_aif_sbv);
 
 void zpci_zdev_put(struct zpci_dev *zdev)
+	__must_hold(&pci_rescan_remove_lock)
 {
 	if (!zdev)
 		return;
+	lockdep_assert_held(&pci_rescan_remove_lock);
 	mutex_lock(&zpci_add_remove_lock);
 	kref_put_lock(&zdev->kref, zpci_release_device, &zpci_list_lock);
 	mutex_unlock(&zpci_add_remove_lock);
@@ -582,11 +584,13 @@ int zpci_setup_bus_resources(struct zpci_dev *zdev)
 }
 
 static void zpci_cleanup_bus_resources(struct zpci_dev *zdev)
+	__must_hold(&pci_rescan_remove_lock)
 {
 	struct resource *res;
 	int i;
 
-	pci_lock_rescan_remove();
+	lockdep_assert_held(&pci_rescan_remove_lock);
+
 	for (i = 0; i < PCI_STD_NUM_BARS; i++) {
 		res = zdev->bars[i].res;
 		if (!res)
@@ -599,7 +603,6 @@ static void zpci_cleanup_bus_resources(struct zpci_dev *zdev)
 		kfree(res);
 	}
 	zdev->has_resources = 0;
-	pci_unlock_rescan_remove();
 }
 
 int pcibios_device_add(struct pci_dev *pdev)
@@ -629,6 +632,7 @@ void pcibios_release_device(struct pci_dev *pdev)
 {
 	struct zpci_dev *zdev = to_zpci(pdev);
 
+	guard(pci_rescan_remove)();
 	zpci_unmap_resources(pdev);
 	zpci_zdev_put(zdev);
 }
@@ -1208,7 +1212,8 @@ static int __init pci_base_init(void)
 	if (rc)
 		goto out_irq;
 
-	rc = zpci_scan_devices();
+	scoped_guard(pci_rescan_remove)
+		rc = zpci_scan_devices();
 	if (rc)
 		goto out_find;
 
diff --git a/arch/s390/pci/pci_bus.c b/arch/s390/pci/pci_bus.c
index 36a4807285fa..c1b48b572e86 100644
--- a/arch/s390/pci/pci_bus.c
+++ b/arch/s390/pci/pci_bus.c
@@ -82,9 +82,8 @@ int zpci_bus_scan_device(struct zpci_dev *zdev)
 	if (!pdev)
 		return -ENODEV;
 
-	pci_lock_rescan_remove();
+	guard(pci_rescan_remove)();
 	pci_bus_add_device(pdev);
-	pci_unlock_rescan_remove();
 
 	return 0;
 }
@@ -132,10 +131,13 @@ void zpci_bus_remove_device(struct zpci_dev *zdev, bool set_error)
  * Return: 0 on success, an error value otherwise
  */
 int zpci_bus_scan_bus(struct zpci_bus *zbus)
+	__must_hold(&pci_rescan_remove_lock)
 {
 	struct zpci_dev *zdev;
 	int devfn, rc, ret = 0;
 
+	lockdep_assert_held(&pci_rescan_remove_lock);
+
 	for (devfn = 0; devfn < ZPCI_FUNCTIONS_PER_BUS; devfn++) {
 		zdev = zbus->function[devfn];
 		if (zdev && zdev->state == ZPCI_FN_STATE_CONFIGURED) {
@@ -145,10 +147,8 @@ int zpci_bus_scan_bus(struct zpci_bus *zbus)
 		}
 	}
 
-	pci_lock_rescan_remove();
 	pci_scan_child_bus(zbus->bus);
 	pci_bus_add_devices(zbus->bus);
-	pci_unlock_rescan_remove();
 
 	return ret;
 }
@@ -214,11 +214,12 @@ static int zpci_bus_create_pci_bus(struct zpci_bus *zbus, struct zpci_dev *fr, s
  * run of the function.
  */
 static inline void zpci_bus_release(struct kref *kref)
-	__releases(&zbus_list_lock)
+	__releases(&zbus_list_lock) __must_hold(&pci_rescan_remove_lock)
 {
 	struct zpci_bus *zbus = container_of(kref, struct zpci_bus, kref);
 
 	lockdep_assert_held(&zbus_list_lock);
+	lockdep_assert_held(&pci_rescan_remove_lock);
 
 	list_del(&zbus->bus_next);
 	mutex_unlock(&zbus_list_lock);
@@ -229,14 +230,12 @@ static inline void zpci_bus_release(struct kref *kref)
 	 */
 
 	if (zbus->bus) {
-		pci_lock_rescan_remove();
 		pci_stop_root_bus(zbus->bus);
 
 		zpci_free_domain(zbus->domain_nr);
 		pci_free_resource_list(&zbus->resources);
 
 		pci_remove_root_bus(zbus->bus);
-		pci_unlock_rescan_remove();
 	}
 
 	zpci_remove_parent_msi_domain(zbus);
@@ -250,7 +249,9 @@ static inline void __zpci_bus_get(struct zpci_bus *zbus)
 }
 
 static inline void zpci_bus_put(struct zpci_bus *zbus)
+	__must_hold(&pci_rescan_remove_lock)
 {
+	lockdep_assert_held(&pci_rescan_remove_lock);
 	kref_put_mutex(&zbus->kref, zpci_bus_release, &zbus_list_lock);
 }
 
diff --git a/arch/s390/pci/pci_event.c b/arch/s390/pci/pci_event.c
index 839bd91c056e..98253706b591 100644
--- a/arch/s390/pci/pci_event.c
+++ b/arch/s390/pci/pci_event.c
@@ -342,6 +342,7 @@ static void __zpci_event_error(struct zpci_ccdf_err *ccdf)
 no_pdev:
 	if (zdev)
 		mutex_unlock(&zdev->state_lock);
+	guard(pci_rescan_remove)();
 	zpci_zdev_put(zdev);
 }
 
@@ -400,9 +401,11 @@ static void __zpci_event_availability(struct zpci_ccdf_avail *ccdf)
 			zdev = zpci_create_device(ccdf->fid, ccdf->fh, ZPCI_FN_STATE_CONFIGURED);
 			if (IS_ERR(zdev))
 				break;
-			if (zpci_add_device(zdev)) {
-				kfree(zdev);
-				break;
+			scoped_guard(pci_rescan_remove) {
+				if (zpci_add_device(zdev)) {
+					kfree(zdev);
+					break;
+				}
 			}
 		} else {
 			if (zdev->state == ZPCI_FN_STATE_RESERVED)
@@ -419,9 +422,11 @@ static void __zpci_event_availability(struct zpci_ccdf_avail *ccdf)
 			zdev = zpci_create_device(ccdf->fid, ccdf->fh, ZPCI_FN_STATE_STANDBY);
 			if (IS_ERR(zdev))
 				break;
-			if (zpci_add_device(zdev)) {
-				kfree(zdev);
-				break;
+			scoped_guard(pci_rescan_remove) {
+				if (zpci_add_device(zdev)) {
+					kfree(zdev);
+					break;
+				}
 			}
 		} else {
 			if (zdev->state == ZPCI_FN_STATE_RESERVED)
@@ -450,24 +455,29 @@ static void __zpci_event_availability(struct zpci_ccdf_avail *ccdf)
 			/* The 0x0304 event may immediately reserve the device */
 			if (!clp_get_state(zdev->fid, &state) &&
 			    state == ZPCI_FN_STATE_RESERVED) {
+				guard(pci_rescan_remove)();
 				zpci_device_reserved(zdev);
 			}
 		}
 		break;
 	case 0x0306: /* 0x308 or 0x302 for multiple devices */
-		zpci_remove_reserved_devices();
-		zpci_scan_devices();
+		scoped_guard(pci_rescan_remove) {
+			zpci_remove_reserved_devices();
+			zpci_scan_devices();
+		}
 		break;
 	case 0x0308: /* Standby -> Reserved */
 		if (!zdev)
 			break;
-		zpci_device_reserved(zdev);
+		scoped_guard(pci_rescan_remove)
+			zpci_device_reserved(zdev);
 		break;
 	default:
 		break;
 	}
 	if (existing_zdev) {
 		mutex_unlock(&zdev->state_lock);
+		guard(pci_rescan_remove)();
 		zpci_zdev_put(zdev);
 	}
 }
diff --git a/arch/s390/pci/pci_iov.c b/arch/s390/pci/pci_iov.c
index 13050ce5c3e9..1f7e4dd018e7 100644
--- a/arch/s390/pci/pci_iov.c
+++ b/arch/s390/pci/pci_iov.c
@@ -38,10 +38,9 @@ void zpci_iov_map_resources(struct pci_dev *pdev)
 
 void zpci_iov_remove_virtfn(struct pci_dev *pdev, int vfn)
 {
-	pci_lock_rescan_remove();
+	guard(pci_rescan_remove)();
 	/* Linux' vfid's start at 0 vfn at 1 */
 	pci_iov_remove_virtfn(pdev->physfn, vfn - 1);
-	pci_unlock_rescan_remove();
 }
 
 static int zpci_iov_link_virtfn(struct pci_dev *pdev, struct pci_dev *virtfn, int vfid)
diff --git a/arch/s390/pci/pci_sysfs.c b/arch/s390/pci/pci_sysfs.c
index c2444a23e26c..f5027aa95928 100644
--- a/arch/s390/pci/pci_sysfs.c
+++ b/arch/s390/pci/pci_sysfs.c
@@ -98,9 +98,9 @@ static ssize_t recover_store(struct device *dev, struct device_attribute *attr,
 	WARN_ON_ONCE(!kn);
 
 	/* Device needs to be configured and state must not change */
-	mutex_lock(&zdev->state_lock);
+	guard(mutex)(&zdev->state_lock);
 	if (zdev->state != ZPCI_FN_STATE_CONFIGURED)
-		goto out;
+		return count;
 
 	/* device_remove_file() serializes concurrent calls ignoring all but
 	 * the first
@@ -112,15 +112,12 @@ static ssize_t recover_store(struct device *dev, struct device_attribute *attr,
 	 * Once it unblocks from pci_lock_rescan_remove() the original pdev
 	 * will already be removed.
 	 */
-	pci_lock_rescan_remove();
+	guard(pci_rescan_remove)();
 	if (pci_dev_is_added(pdev)) {
 		ret = _do_recover(pdev, zdev);
 	}
 	pci_rescan_bus(zdev->zbus->bus);
-	pci_unlock_rescan_remove();
 
-out:
-	mutex_unlock(&zdev->state_lock);
 	if (kn)
 		sysfs_unbreak_active_protection(kn);
 	return ret ? ret : count;
-- 
2.54.0