Re: [PATCH v12 06/31] mm: introduce pte_spinlock for FAULT_FLAG_SPECULATIVE

[Jerome Glisse]

On Tue, Apr 16, 2019 at 03:44:57PM +0200, Laurent Dufour wrote:
> When handling page fault without holding the mmap_sem the fetch of the
> pte lock pointer and the locking will have to be done while ensuring
> that the VMA is not touched in our back.
> 
> So move the fetch and locking operations in a dedicated function.
> 
> Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxx>

Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx>


> ---
>  mm/memory.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index fc3698d13cb5..221ccdf34991 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2073,6 +2073,13 @@ int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
>  }
>  EXPORT_SYMBOL_GPL(apply_to_page_range);
>  
> +static inline bool pte_spinlock(struct vm_fault *vmf)
> +{
> +	vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
> +	spin_lock(vmf->ptl);
> +	return true;
> +}
> +
>  static inline bool pte_map_lock(struct vm_fault *vmf)
>  {
>  	vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd,
> @@ -3656,8 +3663,8 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
>  	 * validation through pte_unmap_same(). It's of NUMA type but
>  	 * the pfn may be screwed if the read is non atomic.
>  	 */
> -	vmf->ptl = pte_lockptr(vma->vm_mm, vmf->pmd);
> -	spin_lock(vmf->ptl);
> +	if (!pte_spinlock(vmf))
> +		return VM_FAULT_RETRY;
>  	if (unlikely(!pte_same(*vmf->pte, vmf->orig_pte))) {
>  		pte_unmap_unlock(vmf->pte, vmf->ptl);
>  		goto out;
> @@ -3850,8 +3857,8 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
>  	if (pte_protnone(vmf->orig_pte) && vma_is_accessible(vmf->vma))
>  		return do_numa_page(vmf);
>  
> -	vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
> -	spin_lock(vmf->ptl);
> +	if (!pte_spinlock(vmf))
> +		return VM_FAULT_RETRY;
>  	entry = vmf->orig_pte;
>  	if (unlikely(!pte_same(*vmf->pte, entry)))
>  		goto unlock;
> -- 
> 2.21.0
>