[PATCH] iommu: WARN_ON when removing a device with no iommu_group associated

[Wei Yang <weiyang@linux.vnet.ibm.com>]

When removing a device from the system, iommu_group driver will try to
disconnect it from its group. While in some cases, one device may not
associated with any iommu_group. For example, not enough DMA address space.

In the generic bus notification, it will check dev->iommu_group before calling
iommu_group_remove_device(). While in some cases, developers may call
iommu_group_remove_device() in a different code path and without check. For
those devices with dev->iommu_group set to NULL, kernel will crash.

This patch gives a warning and return when trying to remove a device from an
iommu_group with dev->iommu_group set to NULL. This helps to indicate some bad
behavior and also guard the kernel.

Signed-off-by: Wei Yang <weiyang@linux.vnet.ibm.com>
---
 drivers/iommu/iommu.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index fbe9ca7..43396f0 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -379,6 +379,9 @@ void iommu_group_remove_device(struct device *dev)
 	struct iommu_group *group = dev->iommu_group;
 	struct iommu_device *tmp_device, *device = NULL;
 
+	if (WARN_ON(!group))
+		return;
+
 	/* Pre-notify listeners that a device is being removed. */
 	blocking_notifier_call_chain(&group->notifier,
 				     IOMMU_GROUP_NOTIFY_DEL_DEVICE, dev);
-- 
1.7.5.4