[kernel,v2,1/2] powerpc/iommu: Stop using @current in mm_iommu_xxx

Nicholas Piggin npiggin at gmail.com
Sat Jul 23 16:33:07 AEST 2016


On Wed, 20 Jul 2016 14:34:30 +1000
Alexey Kardashevskiy <aik at ozlabs.ru> wrote:



>  static long tce_iommu_register_pages(struct tce_container *container,
> @@ -128,10 +129,17 @@ static long tce_iommu_register_pages(struct
> tce_container *container, ((vaddr + size) < vaddr))
>  		return -EINVAL;
>  
> -	ret = mm_iommu_get(vaddr, entries, &mem);
> +	if (!container->mm) {
> +		if (!current->mm)
> +			return -ESRCH; /* process exited */

This shouldn't happen if we're a userspace process.

> +
> +		atomic_inc(&current->mm->mm_count);
> +		container->mm = current->mm;
> +	}
> +
> +	ret = mm_iommu_get(container->mm, vaddr, entries, &mem);

Is it possible for processes (different mm) to be using the same
container? 


> @@ -354,6 +362,8 @@ static void tce_iommu_release(void *iommu_data)
>  		tce_iommu_free_table(tbl);
>  	}
>  
> +	if (container->mm)
> +		mmdrop(container->mm);
>  	tce_iommu_disable(container);
>  	mutex_destroy(&container->lock);

I'm wondering why keep the mm around at all. There is a bit of
locked_vm accounting there (which maybe doesn't exactly do the
right thing if we're talking about current task's rlimit if the
mm does not belong to current anyway).

The interesting cases are only the ones where a thread does
something with container->mm when current->mm != container->mm
(either a different process or a kernel thread). In what
situations does that happen?

Thanks,
Nick


More information about the Linuxppc-dev mailing list