[PATCH v11 0/2] PCI/IOV: Fix SR-IOV locking races and AB-BA deadlock

[PATCH v11 0/2] PCI/IOV: Fix SR-IOV locking races and AB-BA deadlock

[Ionut Nechita (Wind River)]

Hi Bjorn,

This is v11 of the fix for the SR-IOV race between driver .remove()
and concurrent hotplug events.

Changes since v10 (Mar 18):
  - Patch 2/2: added kill_device() before device_release_driver() to
    prevent a new driver from binding between unbind and removal,
    closing the TOCTOU race window identified by Benjamin Block
  - Patch 1/2 unchanged from v10

Changes since v9 (Mar 10):
  - NEW patch 2/2: fix AB-BA deadlock in remove_store() by calling
    device_release_driver() before pci_stop_and_remove_bus_device_locked(),
    as suggested by Benjamin Block (addresses Guenter Roeck's report)
  - Patch 1/2 unchanged from v9

Changes since v8 (Mar 9):
  - Added Reviewed-by from Niklas Schnelle (IBM) and Tested-by (s390)
  - Added Fixes tags for the three related commits
  - Removed rescan/remove locking from sriov_numvfs_store() since
    locking is now handled in sriov_add_vfs() and sriov_del_vfs()
  - Rebased on linux-next (20260309)

The 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

Patch 2/2 fixes this by:
  1. Marking the device as dead via kill_device() so no new driver
     can bind (prevents TOCTOU race between unbind and removal)
  2. Calling device_release_driver() before
     pci_stop_and_remove_bus_device_locked(), so both paths take
     locks in the same order: device_lock first, then
     pci_rescan_remove_lock

Note: the concurrent unbind_store + hotplug-event case (where the
hotplug handler takes pci_rescan_remove_lock before device_lock)
remains a known limitation.  This is a pre-existing issue that
Benjamin Block is addressing separately in:
  https://lore.kernel.org/linux-pci/354b9e4a54ced67f3c89df198041df19434fe4c8.1773235561.git.bblock@linux.ibm.com/

This race has been independently observed by multiple organizations:
  - IBM (s390 platform-generated hot-unplug events racing with
    sriov_del_vfs during PF driver unload)
  - NVIDIA (tested by Dragos Tatulea in earlier versions)
  - Intel (xe driver hitting lockdep warnings and deadlocks when
    calling pci_disable_sriov from .remove)
  - Wind River (original reporter and patch author)

Test environment:
  - Tested on s390 by Benjamin Block and Niklas Schnelle (IBM)
  - Tested on x86_64 with Intel and NVIDIA SR-IOV devices (earlier
    versions)

Based on linux-next (next-20260325).

Link: https://lore.kernel.org/linux-pci/20260214193235.262219-3-ionut.nechita@windriver.com/ [v1]
Link: https://lore.kernel.org/linux-pci/20260219212648.82606-1-ionut.nechita@windriver.com/ [v2]
Link: https://lore.kernel.org/lkml/20260225202434.18737-1-ionut.nechita@windriver.com/ [v3]
Link: https://lore.kernel.org/linux-pci/20260228120138.51197-2-ionut.nechita@windriver.com/ [v4]
Link: https://lore.kernel.org/linux-pci/20260303080903.28693-1-ionut.nechita@windriver.com/ [v5]
Link: https://lore.kernel.org/linux-pci/20260306082108.17322-1-ionut.nechita@windriver.com/ [v6]
Link: https://lore.kernel.org/linux-pci/20260308135352.80346-1-ionut.nechita@windriver.com/ [v7]
Link: https://lore.kernel.org/linux-pci/20260309194920.16459-1-ionut.nechita@windriver.com/ [v8]
Link: https://lore.kernel.org/linux-pci/20260310074303.17480-1-ionut.nechita@windriver.com/ [v9]
Link: https://lore.kernel.org/linux-pci/20260318210316.61975-1-ionut.nechita@windriver.com/ [v10]

Ionut Nechita (Wind River) (2):
  PCI/IOV: Make pci_lock_rescan_remove() reentrant and protect
    sriov_add_vfs/sriov_del_vfs
  PCI: Fix AB-BA deadlock between device_lock and pci_rescan_remove_lock
    in remove_store

 drivers/pci/iov.c       |  9 +++++----
 drivers/pci/pci-sysfs.c | 30 +++++++++++++++++++++++++++++-
 drivers/pci/probe.c     | 11 +++++++++--
 3 files changed, 43 insertions(+), 7 deletions(-)

--
2.53.0

[PATCH v11 1/2] PCI/IOV: Make pci_lock_rescan_remove() reentrant and protect sriov_add_vfs/sriov_del_vfs

[Ionut Nechita (Wind River)]

After reverting commit 05703271c3cd ("PCI/IOV: Add PCI rescan-remove
locking when enabling/disabling SR-IOV") and moving the lock to
sriov_numvfs_store(), the path through driver .remove() (e.g. rmmod,
or manual unbind) that calls pci_disable_sriov() directly remains
unprotected against concurrent hotplug events. This affects any SR-IOV
capable driver that calls pci_disable_sriov() from its .remove()
callback (i40e, ice, mlx5, bnxt, etc.).

On s390, platform-generated hot-unplug events for VFs can race with
sriov_del_vfs() when a PF driver is being unloaded. The platform event
handler takes pci_rescan_remove_lock, but sriov_del_vfs() does not,
leading to double removal and list corruption.

We cannot use a plain mutex_lock() here because sriov_del_vfs() may also
be called from paths that already hold pci_rescan_remove_lock (e.g.
remove_store -> pci_stop_and_remove_bus_device_locked, or
sriov_numvfs_store with the lock taken by the previous patch). Using
mutex_lock() in those cases would deadlock.

Make pci_lock_rescan_remove() itself reentrant using mutex_get_owner()
and a reentrant depth counter, as suggested by Lukas Wunner and
Benjamin Block, since these recursive locking scenarios exist elsewhere
in the PCI subsystem:
 - If the lock is already held by the current task (checked via
   mutex_get_owner()): increments the reentrant counter and returns
   without re-acquiring, avoiding deadlock.
 - If the lock is held by another task: blocks until the lock is
   released, providing complete serialization.
 - If the lock is not held: acquires the mutex normally.

pci_unlock_rescan_remove() decrements the reentrant counter if it is
non-zero, otherwise releases the mutex.

This approach keeps the API unchanged: callers simply pair lock/unlock
calls without needing to track any return value or use separate
reentrant variants.

Add pci_lock_rescan_remove()/pci_unlock_rescan_remove() calls to
sriov_add_vfs() and sriov_del_vfs() to protect VF addition and
removal against concurrent hotplug events.

Remove the rescan/remove locking from sriov_numvfs_store() that was
introduced by commit a5338e365c45 ("PCI/IOV: Fix race between SR-IOV
enable/disable and hotplug"), since the locking is now handled directly
in sriov_add_vfs() and sriov_del_vfs() where it is actually needed,
reducing the lock scope.

Fixes: 18f9e9d150fc ("PCI/IOV: Factor out sriov_add_vfs()")
Fixes: 05703271c3cd ("PCI/IOV: Add PCI rescan-remove locking when enabling/disabling SR-IOV")
Fixes: a5338e365c45 ("PCI/IOV: Fix race between SR-IOV enable/disable and hotplug")
Cc: stable@vger.kernel.org
Suggested-by: Lukas Wunner <lukas@wunner.de>
Suggested-by: Benjamin Block <bblock@linux.ibm.com>
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Tested-by: Benjamin Block <bblock@linux.ibm.com>
Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com> # s390
Signed-off-by: Ionut Nechita <ionut.nechita@windriver.com>
---
 drivers/pci/iov.c   |  9 +++++----
 drivers/pci/probe.c | 11 +++++++++--
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index 91ac4e37ecb9c..7ed902539051e 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -495,9 +495,7 @@ static ssize_t sriov_numvfs_store(struct device *dev,
 
 	if (num_vfs == 0) {
 		/* disable VFs */
-		pci_lock_rescan_remove();
 		ret = pdev->driver->sriov_configure(pdev, 0);
-		pci_unlock_rescan_remove();
 		goto exit;
 	}
 
@@ -509,9 +507,7 @@ static ssize_t sriov_numvfs_store(struct device *dev,
 		goto exit;
 	}
 
-	pci_lock_rescan_remove();
 	ret = pdev->driver->sriov_configure(pdev, num_vfs);
-	pci_unlock_rescan_remove();
 	if (ret < 0)
 		goto exit;
 
@@ -633,15 +629,18 @@ static int sriov_add_vfs(struct pci_dev *dev, u16 num_vfs)
 	if (dev->no_vf_scan)
 		return 0;
 
+	pci_lock_rescan_remove();
 	for (i = 0; i < num_vfs; i++) {
 		rc = pci_iov_add_virtfn(dev, i);
 		if (rc)
 			goto failed;
 	}
+	pci_unlock_rescan_remove();
 	return 0;
 failed:
 	while (i--)
 		pci_iov_remove_virtfn(dev, i);
+	pci_unlock_rescan_remove();
 
 	return rc;
 }
@@ -766,8 +765,10 @@ static void sriov_del_vfs(struct pci_dev *dev)
 	struct pci_sriov *iov = dev->sriov;
 	int i;
 
+	pci_lock_rescan_remove();
 	for (i = 0; i < iov->num_VFs; i++)
 		pci_iov_remove_virtfn(dev, i);
+	pci_unlock_rescan_remove();
 }
 
 static void sriov_disable(struct pci_dev *dev)
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index bccc7a4bdd794..ce4d351b5aa21 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -3509,16 +3509,23 @@ EXPORT_SYMBOL_GPL(pci_rescan_bus);
  * routines should always be executed under this mutex.
  */
 DEFINE_MUTEX(pci_rescan_remove_lock);
+static size_t pci_rescan_remove_reentrant_count;
 
 void pci_lock_rescan_remove(void)
 {
-	mutex_lock(&pci_rescan_remove_lock);
+	if (mutex_get_owner(&pci_rescan_remove_lock) == (unsigned long)current)
+		pci_rescan_remove_reentrant_count++;
+	else
+		mutex_lock(&pci_rescan_remove_lock);
 }
 EXPORT_SYMBOL_GPL(pci_lock_rescan_remove);
 
 void pci_unlock_rescan_remove(void)
 {
-	mutex_unlock(&pci_rescan_remove_lock);
+	if (pci_rescan_remove_reentrant_count > 0)
+		pci_rescan_remove_reentrant_count--;
+	else
+		mutex_unlock(&pci_rescan_remove_lock);
 }
 EXPORT_SYMBOL_GPL(pci_unlock_rescan_remove);
 
-- 
2.53.0

[PATCH v11 2/2] PCI: Fix AB-BA deadlock between device_lock and pci_rescan_remove_lock in remove_store

[Ionut Nechita (Wind River)]

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
Signed-off-by: Ionut Nechita <ionut.nechita@windriver.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 a2f8a5d6190fd..e87aa96c02bde 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -518,8 +518,36 @@ 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,
-- 
2.53.0