[PATCH v9 0/1] PCI/IOV: Make pci_lock_rescan_remove() reentrant and protect sriov_add_vfs/sriov_del_vfs

[PATCH v9 0/1] PCI/IOV: Make pci_lock_rescan_remove() reentrant and protect sriov_add_vfs/sriov_del_vfs

[Ionut Nechita (Wind River)]

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

Hi Bjorn,

This is v9 of the fix for the SR-IOV race between driver .remove()
and concurrent hotplug events (particularly on s390).

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, as reported and discussed
   in https://lore.kernel.org/all/20260227214048.12649-1-michal.wajdeczko@intel.com/)
 - Wind River (original reporter and patch author)

Changes since v8 (Mar 9):
- Added Reviewed-by from Niklas Schnelle (IBM) and Tested-by (s390)
- Added Fixes tags for commits 05703271c3cd ("PCI/IOV: Add PCI
  rescan-remove locking when enabling/disabling SR-IOV") and
  a5338e365c45 ("PCI/IOV: Fix race between SR-IOV enable/disable
  and hotplug"), as suggested by Niklas Schnelle
- Removed the rescan/remove locking from sriov_numvfs_store() that
  was introduced by commit a5338e365c45, since the locking is now
  handled directly in sriov_add_vfs() and sriov_del_vfs() where it
  is actually needed, reducing the lock scope (suggested by Niklas
  Schnelle)
- Rebased on linux-next (20260309)

Changes since v7 (Mar 8):
- Added Reviewed-by and Tested-by from Benjamin Block (IBM), who
  ran tests in the IBM s390 test lab
- Rebased on linux-next (20260309)
- No code changes from v7

Changes since v6 (Mar 6):
- Replaced local pci_rescan_remove_owner / pci_rescan_remove_count
  variables with mutex_get_owner() for owner checking and a single
  pci_rescan_remove_reentrant_count depth counter, as tested and
  suggested by Benjamin Block
- Dropped Reviewed-by and Tested-by tags per Benjamin Block's
  feedback, since the implementation changed substantially between
  the reviewed version and the current one
- Added Suggested-by for Benjamin Block
- Rebased on linux-next (20260306)

Changes since v5 (Mar 3):
- Reworked based on Lukas Wunner's suggestion: instead of introducing
  separate pci_lock_rescan_remove_reentrant() /
  pci_unlock_rescan_remove_reentrant() helpers, make the existing
  pci_lock_rescan_remove() / pci_unlock_rescan_remove() themselves
  reentrant using owner tracking and a depth counter
- No new API: callers simply use pci_lock/unlock_rescan_remove()
  without needing to track any return value
- No changes to include/linux/pci.h
- Rebased on linux-next (20260306)

Changes since v4 (Feb 28):
- Replaced local pci_rescan_remove_owner variable with
  mutex_get_owner() to check lock ownership, as suggested by
  Manivannan Sadhasivam and agreed by Benjamin Block
- Removed owner tracking from pci_lock_rescan_remove() and
  pci_unlock_rescan_remove() - they are now unchanged from upstream
- Rebased on linux-next (20260302)

Changes since v3 (Feb 25):
- Rebased on linux-next (next-20260227)
- Declared pci_rescan_remove_owner as const pointer
  (const struct task_struct *) to make clear it is not meant to
  modify the task (Benjamin Block)
- Added Reviewed-by and Tested-by from Benjamin Block (IBM)

Changes since v2 (Feb 19):
- Rebased on linux-next (next-20260225)
- Added Tested-by from Dragos Tatulea (NVIDIA)
- No code changes from v2

Changes since v1 (Feb 14):
- Renamed from pci_lock_rescan_remove_nested() to
  pci_lock_rescan_remove_reentrant() to avoid confusion with
  mutex_lock_nested() lockdep annotations (Benjamin Block)
- Added pci_unlock_rescan_remove_reentrant(const bool locked) helper
  to avoid open-coding conditional unlock at each call site
  (Benjamin Block)
- Moved declarations from drivers/pci/pci.h to include/linux/pci.h
  alongside existing lock/unlock declarations (Benjamin Block)
- Simplified callers: removed negation of return value and manual
  conditional unlock in favor of the paired lock/unlock helpers

The problem: 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() because
sriov_del_vfs() may be called from paths that already hold the
lock (deadlock), and mutex_trylock() cannot distinguish self from
other holders.

The same class of problem has been observed on Intel xe, where
pci_disable_sriov() is called from the driver's .remove() callback
without pci_rescan_remove_lock, but .remove() may itself be called
from a path that already holds the lock (e.g. remove_store ->
pci_stop_and_remove_bus_device_locked), leading to lockdep warnings
and potential deadlocks.

The fix makes pci_lock_rescan_remove() reentrant using
mutex_get_owner() and a depth counter: if the current task already
holds the lock, the counter is incremented;
pci_unlock_rescan_remove() decrements the counter and only releases
the mutex when it reaches zero. This keeps the existing API unchanged
while providing correct serialization.

The rescan/remove locking in sriov_numvfs_store() (from commit
a5338e365c45) is removed since the locking is now handled directly
in sriov_add_vfs() and sriov_del_vfs(), reducing the lock scope.

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/linux-pci/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]

Ionut Nechita (Wind River) (1):
  PCI/IOV: Make pci_lock_rescan_remove() reentrant and protect
    sriov_add_vfs/sriov_del_vfs

 drivers/pci/iov.c   |  9 +++++----
 drivers/pci/probe.c | 11 +++++++++--
 2 files changed, 14 insertions(+), 6 deletions(-)


base-commit: c8be6ef92d9bc54f012627375b87b44d3eefe451
--
2.53.0

[PATCH v9 1/1] PCI/IOV: Make pci_lock_rescan_remove() reentrant and protect sriov_add_vfs/sriov_del_vfs

[Ionut Nechita (Wind River)]

From: Ionut Nechita <ionut_n2001@yahoo.com>

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_n2001@yahoo.com>
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