Re: [PATCH 19/22] mm: always return EBUSY for invalid ranges in hmm_range_{fault,snapshot}

[Ralph Campbell <rcampbell@xxxxxxxxxx>]

On 6/30/19 11:20 PM, Christoph Hellwig wrote:
> We should not have two different error codes for the same condition.  In
> addition this really complicates the code due to the special handling of
> EAGAIN that drops the mmap_sem due to the FAULT_FLAG_ALLOW_RETRY logic
> in the core vm.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>

Reviewed-by: Ralph Campbell <rcampbell@xxxxxxxxxx>

Probably should update the "Return:" comment above
hmm_range_snapshot() too.

> ---
>   mm/hmm.c | 8 +++-----
>   1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/mm/hmm.c b/mm/hmm.c
> index c85ed7d4e2ce..d125df698e2b 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -974,7 +974,7 @@ long hmm_range_snapshot(struct hmm_range *range)
>   	do {
>   		/* If range is no longer valid force retry. */
>   		if (!range->valid)
> -			return -EAGAIN;
> +			return -EBUSY;
>   
>   		vma = find_vma(hmm->mm, start);
>   		if (vma == NULL || (vma->vm_flags & device_vma))
> @@ -1069,10 +1069,8 @@ long hmm_range_fault(struct hmm_range *range, bool block)
>   
>   	do {
>   		/* If range is no longer valid force retry. */
> -		if (!range->valid) {
> -			up_read(&hmm->mm->mmap_sem);
> -			return -EAGAIN;
> -		}
> +		if (!range->valid)
> +			return -EBUSY;
>   
>   		vma = find_vma(hmm->mm, start);
>   		if (vma == NULL || (vma->vm_flags & device_vma))