iommu/vt-d: Avoid use of NULL after WARN_ON_ONCE

[ Upstream commit 60f030f ]

There is a WARN_ON_ONCE to catch an unlikely situation when
domain_remove_dev_pasid can't find the `pasid`. In case it nevertheless
happens we must avoid using a NULL pointer.

Signed-off-by: Kees Bakker <kees@ijzerbout.nl>
Link: https://lore.kernel.org/r/20241218201048.E544818E57E@bout3.ijzerbout.nl
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Amelia Crate <acrate@waldn.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: keestux

drivers/iommu/intel/iommu.c

@@ -4328,13 +4328,14 @@ static void intel_iommu_remove_dev_pasid(struct device *dev, ioasid_t pasid,
 			break;
 		}
 	}
-	WARN_ON_ONCE(!dev_pasid);
 	spin_unlock_irqrestore(&dmar_domain->lock, flags);
 
 	cache_tag_unassign_domain(dmar_domain, dev, pasid);
 	domain_detach_iommu(dmar_domain, iommu);
-	intel_iommu_debugfs_remove_dev_pasid(dev_pasid);
-	kfree(dev_pasid);
+	if (!WARN_ON_ONCE(!dev_pasid)) {
+		intel_iommu_debugfs_remove_dev_pasid(dev_pasid);
+		kfree(dev_pasid);
+	}
 	intel_pasid_tear_down_entry(iommu, dev, pasid, false);
 	intel_drain_pasid_prq(dev, pasid);
 }