[PATCH v5 1/1] PCI/IOV: Add reentrant locking in sriov_add_vfs/sriov_del_vfs for complete serialization

["Ionut Nechita (Wind River)" <ionut.nechita@windriver.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.

Instead, introduce a pci_lock_rescan_remove_reentrant() helper that uses
mutex_get_owner() to check if the current task already holds the lock:
 - If the lock is not held: acquires it and returns true, providing
   full serialization against concurrent hotplug events (including
   platform-generated events on s390).
 - If the lock is already held by the current task (reentrant call from
   remove_store or sriov_numvfs_store paths): returns false without
   re-acquiring, avoiding deadlock while the caller already provides
   the necessary serialization.
 - If the lock is held by another task (concurrent hotplug): blocks
   until the lock is released, then acquires it, providing complete
   serialization. This is the key improvement over a trylock approach.

A matching pci_unlock_rescan_remove_reentrant() helper takes the return
value of the lock function as argument, so callers don't need to
open-code the conditional unlock.

The "reentrant" naming is chosen to avoid confusion with existing
mutex_lock_nested() which is a lockdep annotation concept, not actual
reentrant locking.

The declarations are placed in include/linux/pci.h alongside the existing
pci_lock_rescan_remove()/pci_unlock_rescan_remove() declarations to
maintain API consistency and allow use by external drivers if needed.

Fixes: 18f9e9d150fc ("PCI/IOV: Factor out sriov_add_vfs()")
Cc: stable@vger.kernel.org
Tested-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Tested-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Ionut Nechita <ionut_n2001@yahoo.com>
Signed-off-by: Ionut Nechita <ionut.nechita@windriver.com>
---
Changes in v5:
 - Replaced local pci_rescan_remove_owner variable with
   mutex_get_owner() to check lock ownership, avoiding the need
   to modify pci_lock_rescan_remove()/pci_unlock_rescan_remove()
   (Manivannan Sadhasivam, Benjamin Block)
 - Rebased on linux-next (20260302)

Changes in v4:
 - 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 in v3:
 - Rebased on linux-next (next-20260225)
 - Added Tested-by from Dragos Tatulea (NVIDIA)
 - No code changes from v2

Changes in v2:
 - 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

 drivers/pci/iov.c   |  7 +++++++
 drivers/pci/probe.c | 16 ++++++++++++++++
 include/linux/pci.h |  2 ++
 3 files changed, 25 insertions(+)

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index 91ac4e37ecb9..adbe4ecc587c 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -629,19 +629,23 @@ static int sriov_add_vfs(struct pci_dev *dev, u16 num_vfs)
 {
 	unsigned int i;
 	int rc;
+	bool locked;
 
 	if (dev->no_vf_scan)
 		return 0;
 
+	locked = pci_lock_rescan_remove_reentrant();
 	for (i = 0; i < num_vfs; i++) {
 		rc = pci_iov_add_virtfn(dev, i);
 		if (rc)
 			goto failed;
 	}
+	pci_unlock_rescan_remove_reentrant(locked);
 	return 0;
 failed:
 	while (i--)
 		pci_iov_remove_virtfn(dev, i);
+	pci_unlock_rescan_remove_reentrant(locked);
 
 	return rc;
 }
@@ -764,10 +768,13 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
 static void sriov_del_vfs(struct pci_dev *dev)
 {
 	struct pci_sriov *iov = dev->sriov;
+	bool locked;
 	int i;
 
+	locked = pci_lock_rescan_remove_reentrant();
 	for (i = 0; i < iov->num_VFs; i++)
 		pci_iov_remove_virtfn(dev, i);
+	pci_unlock_rescan_remove_reentrant(locked);
 }
 
 static void sriov_disable(struct pci_dev *dev)
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index bccc7a4bdd79..86c8f593e0cd 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -3522,6 +3522,22 @@ void pci_unlock_rescan_remove(void)
 }
 EXPORT_SYMBOL_GPL(pci_unlock_rescan_remove);
 
+bool pci_lock_rescan_remove_reentrant(void)
+{
+	if (mutex_get_owner(&pci_rescan_remove_lock) == (unsigned long)current)
+		return false;
+	pci_lock_rescan_remove();
+	return true;
+}
+EXPORT_SYMBOL_GPL(pci_lock_rescan_remove_reentrant);
+
+void pci_unlock_rescan_remove_reentrant(const bool locked)
+{
+	if (locked)
+		pci_unlock_rescan_remove();
+}
+EXPORT_SYMBOL_GPL(pci_unlock_rescan_remove_reentrant);
+
 static int __init pci_sort_bf_cmp(const struct device *d_a,
 				  const struct device *d_b)
 {
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 1c270f1d5123..080950f0bab3 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1535,6 +1535,8 @@ void set_pcie_hotplug_bridge(struct pci_dev *pdev);
 unsigned int pci_rescan_bus(struct pci_bus *bus);
 void pci_lock_rescan_remove(void);
 void pci_unlock_rescan_remove(void);
+bool pci_lock_rescan_remove_reentrant(void);
+void pci_unlock_rescan_remove_reentrant(const bool locked);
 
 /* Vital Product Data routines */
 ssize_t pci_read_vpd(struct pci_dev *dev, loff_t pos, size_t count, void *buf);
-- 
2.53.0