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

[Alex Williamson <alex.williamson@redhat.com>]

[+cc iommu]

On Fri, 2013-08-23 at 09:55 +0800, Wei Yang wrote:
> 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>

Acked-by: Alex Williamson <alex.williamson@redhat.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);