[PATCH hmm 3/8] mm/hmm: do not call hmm_vma_walk_hole() while holding a spinlock

[Ralph Campbell]

On 3/11/20 11:35 AM, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg at mellanox.com>
> 
> This eventually calls into handle_mm_fault() which is a sleeping function.
> Release the lock first.
> 
> hmm_vma_walk_hole() does not touch the contents of the PUD, so it does not
> need the lock.
> 
> Fixes: 3afc423632a1 ("mm: pagewalk: add p4d_entry() and pgd_entry()")
> Cc: Steven Price <steven.price at arm.com>
> Signed-off-by: Jason Gunthorpe <jgg at mellanox.com>

Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>

> ---
>   mm/hmm.c | 14 +++++++-------
>   1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 9e8f68eb83287a..32dcbfd3908315 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -473,8 +473,8 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
>   
>   	pud = READ_ONCE(*pudp);
>   	if (pud_none(pud)) {
> -		ret = hmm_vma_walk_hole(start, end, -1, walk);
> -		goto out_unlock;
> +		spin_unlock(ptl);
> +		return hmm_vma_walk_hole(start, end, -1, walk);
>   	}
>   
>   	if (pud_huge(pud) && pud_devmap(pud)) {
> @@ -483,8 +483,8 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
>   		bool fault, write_fault;
>   
>   		if (!pud_present(pud)) {
> -			ret = hmm_vma_walk_hole(start, end, -1, walk);
> -			goto out_unlock;
> +			spin_unlock(ptl);
> +			return hmm_vma_walk_hole(start, end, -1, walk);
>   		}
>   
>   		i = (addr - range->start) >> PAGE_SHIFT;
> @@ -495,9 +495,9 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
>   		hmm_range_need_fault(hmm_vma_walk, pfns, npages,
>   				     cpu_flags, &fault, &write_fault);
>   		if (fault || write_fault) {
> -			ret = hmm_vma_walk_hole_(addr, end, fault,
> -						 write_fault, walk);
> -			goto out_unlock;
> +			spin_unlock(ptl);
> +			return hmm_vma_walk_hole_(addr, end, fault, write_fault,
> +						  walk);
>   		}
>   
>   		pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
>