linux-kernel - Re: [PATCH] iommu: WARN_ON when removing a device with no iommu

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Message-ID: <1377228807.25163.33.camel@ul30vt.home>
Date:	Thu, 22 Aug 2013 21:33:27 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Wei Yang <weiyang@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	aik@...abs.ru, paulus@....ibm.com, benh@....ibm.com,
	iommu <iommu@...ts.linux-foundation.org>
Subject: Re: [PATCH] iommu: WARN_ON when removing a device with no
 iommu_group associated

[+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@...ux.vnet.ibm.com>

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



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