[RFC v3 03/17] mm: Introduce pte_spinlock

[Laurent Dufour]

This is needed because in handle_pte_fault() pte_offset_map() is
called and then fe->ptl is fetched and spin_locked.

This was previously embedded in the call to pte_offset_map_lock().

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 bce32c9d73c2..441c0e3f3a0f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2100,6 +2100,13 @@ 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;
+}
+
 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);
@@ -3398,8 +3405,8 @@ static int do_numa_page(struct vm_fault *vmf)
 	* page table entry is not accessible, so there would be no
 	* concurrent hardware modifications to the PTE.
 	*/
-	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, pte))) {
 		pte_unmap_unlock(vmf->pte, vmf->ptl);
 		goto out;
@@ -3566,8 +3573,8 @@ 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;
-- 
2.7.4