[PATCH v1 1/6] iommu/dmar: Fix crash on boot when DMAR is disabled

[Andy Shevchenko <andriy.shevchenko-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>]

By default CONFIG_INTEL_IOMMU_DEFAULT_ON is not set and thus
dmar_disabled variable is set.

Intel IOMMU driver based on above doesn't set intel_iommu_enabled
variable.

The commit b0119e870837 ("iommu: Introduce new 'struct iommu_device'")
mistakenly assumes it never happens and tries to unregister not ever
registered resources, which crashes the kernel at boot time:

	BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
	IP: iommu_device_unregister+0x31/0x60

Make unregister procedure conditional in free_iommu().

Fixes: b0119e870837 ("iommu: Introduce new 'struct iommu_device'")
Cc: Joerg Roedel <jroedel-l3A5Bk7waGM@public.gmane.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
---
 drivers/iommu/dmar.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c
index d9c0decfc91a..36e3f430d265 100644
--- a/drivers/iommu/dmar.c
+++ b/drivers/iommu/dmar.c
@@ -1108,8 +1108,10 @@ static int alloc_iommu(struct dmar_drhd_unit *drhd)
 
 static void free_iommu(struct intel_iommu *iommu)
 {
-	iommu_device_sysfs_remove(&iommu->iommu);
-	iommu_device_unregister(&iommu->iommu);
+	if (intel_iommu_enabled) {
+		iommu_device_unregister(&iommu->iommu);
+		iommu_device_sysfs_remove(&iommu->iommu);
+	}
 
 	if (iommu->irq) {
 		if (iommu->pr_irq) {
-- 
2.11.0