Subject: Re: [RFC PATCH kernel] vfio/spapr_tce: Get rid of possible infinite loop

From: David Gibson <[email-masked]>
Date: Tue, 2 Oct 2018 14:44:33 +1000

On Tue, Oct 02, 2018 at 01:22:31PM +1000, Alexey Kardashevskiy wrote:
> As a part of cleanup, the SPAPR TCE IOMMU subdriver releases preregistered
> memory. If there is a bug in memory release, the loop in
> tce_iommu_release() becomes infinite; this actually happened to me.
> 
> This makes the loop finite and prints a warning on every failure to make
> the code more bug prone.
> 
> Signed-off-by: Alexey Kardashevskiy <[email-masked]>

Reviewed-by: David Gibson <[email-masked]>

It does improve the current behaviour.  I do suspect, however, that
leaving the failed regions in the list will probably cause another
failure later on.

> ---
>  drivers/vfio/vfio_iommu_spapr_tce.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> index b1a8ab3..ece0651 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -371,6 +371,7 @@ static void tce_iommu_release(void *iommu_data)
>  {
>  	struct tce_container *container = iommu_data;
>  	struct tce_iommu_group *tcegrp;
> +	struct tce_iommu_prereg *tcemem, *tmtmp;
>  	long i;
>  
>  	while (tce_groups_attached(container)) {
> @@ -393,13 +394,8 @@ static void tce_iommu_release(void *iommu_data)
>  		tce_iommu_free_table(container, tbl);
>  	}
>  
> -	while (!list_empty(&container->prereg_list)) {
> -		struct tce_iommu_prereg *tcemem;
> -
> -		tcemem = list_first_entry(&container->prereg_list,
> -				struct tce_iommu_prereg, next);
> -		WARN_ON_ONCE(tce_iommu_prereg_free(container, tcemem));
> -	}
> +	list_for_each_entry_safe(tcemem, tmtmp, &container->prereg_list, next)
> +		WARN_ON(tce_iommu_prereg_free(container, tcemem));
>  
>  	tce_iommu_disable(container);
>  	if (container->mm)

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson