Re: [PATCH] pseries/iommu: remove iommu device references via bus notifier

[Alexey Kardashevskiy <aik@au1.ibm.com>]

On 02/20/2015 05:41 AM, Nishanth Aravamudan wrote:
> After d905c5df9aef ("PPC: POWERNV: move iommu_add_device earlier"), the
> refcnt on the kobject backing the IOMMU group for a PCI device is
> elevated by each call to pci_dma_dev_setup_pSeriesLP() (via
> set_iommu_table_base_and_group). When we go to dlpar a multi-function
> PCI device out:
>
> 	iommu_reconfig_notifier ->
> 		iommu_free_table ->
> 			iommu_group_put
> 			BUG_ON(tbl->it_group)
>
> We trip this BUG_ON, because there are still references on the table, so
> it is not freed. Fix this by also adding a bus notifier identical to
> PowerNV for pSeries. Tested a remove -> add -> remove cycle without
> issue where it always hit the BUG_ON without the changes.
>
> Fixes: d905c5df9aef ("PPC: POWERNV: move iommu_add_device earlier")
> Signed-off-by: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
> Cc: stable@kernel.org (3.13+)

Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>


> diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
> index 1d3d52dc3ff3..f77fb02f4710 100644
> --- a/arch/powerpc/platforms/pseries/iommu.c
> +++ b/arch/powerpc/platforms/pseries/iommu.c
> @@ -1340,3 +1340,31 @@ static int __init disable_multitce(char *str)
>   }
>
>   __setup("multitce=", disable_multitce);
> +
> +static int tce_iommu_bus_notifier(struct notifier_block *nb,
> +                unsigned long action, void *data)
> +{
> +        struct device *dev = data;
> +
> +        switch (action) {
> +        case BUS_NOTIFY_ADD_DEVICE:
> +                return iommu_add_device(dev);
> +        case BUS_NOTIFY_DEL_DEVICE:
> +                if (dev->iommu_group)
> +                        iommu_del_device(dev);
> +                return 0;
> +        default:
> +                return 0;
> +        }
> +}
> +
> +static struct notifier_block tce_iommu_bus_nb = {
> +        .notifier_call = tce_iommu_bus_notifier,
> +};
> +
> +static int __init tce_iommu_bus_notifier_init(void)
> +{
> +        bus_register_notifier(&pci_bus_type, &tce_iommu_bus_nb);
> +        return 0;
> +}
> +machine_subsys_initcall_sync(pseries, tce_iommu_bus_notifier_init);
>


-- 
Alexey Kardashevskiy
IBM OzLabs, LTC Team

e-mail: aik@au1.ibm.com
notes: Alexey Kardashevskiy/Australia/IBM