[PATCH v2 4/6] mm: Handle COW faults under the VMA lock

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

If the page is not currently present in the page tables, we need to call
the page fault handler to find out which page we're supposed to COW,
so we need to both check that there is already an anon_vma and that the
fault handler doesn't need the mmap_lock.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/memory.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index a9b0c135209a..938f481df0ab 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4639,13 +4639,11 @@ static vm_fault_t do_cow_fault(struct vm_fault *vmf)
 	struct vm_area_struct *vma = vmf->vma;
 	vm_fault_t ret;
 
-	if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
-		vma_end_read(vma);
-		return VM_FAULT_RETRY;
-	}
-
-	if (unlikely(anon_vma_prepare(vma)))
-		return VM_FAULT_OOM;
+	ret = vmf_can_call_fault(vmf);
+	if (!ret)
+		ret = vmf_anon_prepare(vmf);
+	if (ret)
+		return ret;
 
 	vmf->cow_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vmf->address);
 	if (!vmf->cow_page)
-- 
2.40.1