[PATCH 6.19 725/844] PCI/IOV: Fix race between SR-IOV enable/disable and hotplug

[Sasha Levin]

From: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>

[ Upstream commit a5338e365c4559d7b4d7356116b0eb95b12e08d5 ]

Commit 05703271c3cd ("PCI/IOV: Add PCI rescan-remove locking when
enabling/disabling SR-IOV") tried to fix a race between the VF removal
inside sriov_del_vfs() and concurrent hot unplug by taking the PCI
rescan/remove lock in sriov_del_vfs(). Similarly the PCI rescan/remove lock
was also taken in sriov_add_vfs() to protect addition of VFs.

This approach however causes deadlock on trying to remove PFs with SR-IOV
enabled because PFs disable SR-IOV during removal and this removal happens
under the PCI rescan/remove lock. So the original fix had to be reverted.

Instead of taking the PCI rescan/remove lock in sriov_add_vfs() and
sriov_del_vfs(), fix the race that occurs with SR-IOV enable and disable vs
hotplug higher up in the callchain by taking the lock in
sriov_numvfs_store() before calling into the driver's sriov_configure()
callback.

Fixes: 05703271c3cd ("PCI/IOV: Add PCI rescan-remove locking when enabling/disabling SR-IOV")
Reported-by: Benjamin Block <bblock@xxxxxxxxxxxxx>
Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Reviewed-by: Benjamin Block <bblock@xxxxxxxxxxxxx>
Reviewed-by: Gerd Bayer <gbayer@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://patch.msgid.link/20251216-revert_sriov_lock-v3-2-dac4925a7621@xxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/pci/iov.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index 7de5b18647beb..4a659c34935e1 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -495,7 +495,9 @@ 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;
 	}
 
@@ -507,7 +509,9 @@ 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;
 
-- 
2.51.0