On 06/16/2017 11:22 PM, 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.
It does not change things from whats happening right now, where do we
check that VMA has not changed by now ?
>
> So move the fetch and locking operations in a dedicated function.
>
> Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx>
> ---
> mm/memory.c | 15 +++++++++++----
> 1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 40834444ea0d..f1132f7931ef 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2240,6 +2240,13 @@ static inline void wp_page_reuse(struct vm_fault *vmf)
> pte_unmap_unlock(vmf->pte, vmf->ptl);
> }
>
> +static bool pte_spinlock(struct vm_fault *vmf)
> +{
> + vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
> + spin_lock(vmf->ptl);
> + return true;
> +}
> +
Moving them together makes sense but again if blocks are redundant when
it returns true all the time.
> static bool pte_map_lock(struct vm_fault *vmf)
> {
> vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, vmf->address, &vmf->ptl);
> @@ -3552,8 +3559,8 @@ static int 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;
> @@ -3745,8 +3752,8 @@ static int 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;
>
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