1 files changed, 32 insertions, 19 deletions

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index d06453fa8aba..7d5d709cc838 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -86,14 +86,10 @@ static struct vm_area_struct *uffd_lock_vma(struct mm_struct *mm,
 	mmap_read_lock(mm);
 	vma = find_vma_and_prepare_anon(mm, address);
 	if (!IS_ERR(vma)) {
-		/*
-		 * We cannot use vma_start_read() as it may fail due to
-		 * false locked (see comment in vma_start_read()). We
-		 * can avoid that by directly locking vm_lock under
-		 * mmap_lock, which guarantees that nobody can lock the
-		 * vma for write (vma_start_write()) under us.
-		 */
-		down_read(&vma->vm_lock->lock);
+		bool locked = vma_start_read_locked(vma);
+
+		if (!locked)
+			vma = ERR_PTR(-EAGAIN);
 	}
 
 	mmap_read_unlock(mm);
@@ -1563,16 +1559,24 @@ static int uffd_move_lock(struct mm_struct *mm,
 
 	mmap_read_lock(mm);
 	err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
-	if (!err) {
-		/*
-		 * See comment in uffd_lock_vma() as to why not using
-		 * vma_start_read() here.
-		 */
-		down_read(&(*dst_vmap)->vm_lock->lock);
-		if (*dst_vmap != *src_vmap)
-			down_read_nested(&(*src_vmap)->vm_lock->lock,
-					 SINGLE_DEPTH_NESTING);
+	if (err)
+		goto out;
+
+	if (!vma_start_read_locked(*dst_vmap)) {
+		err = -EAGAIN;
+		goto out;
 	}
+
+	/* Nothing further to do if both vmas are locked. */
+	if (*dst_vmap == *src_vmap)
+		goto out;
+
+	if (!vma_start_read_locked_nested(*src_vmap, SINGLE_DEPTH_NESTING)) {
+		/* Undo dst_vmap locking if src_vmap failed to lock */
+		vma_end_read(*dst_vmap);
+		err = -EAGAIN;
+	}
+out:
 	mmap_read_unlock(mm);
 	return err;
 }
@@ -1898,6 +1902,14 @@ struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi,
 					     unsigned long end)
 {
 	struct vm_area_struct *ret;
+	bool give_up_on_oom = false;
+
+	/*
+	 * If we are modifying only and not splitting, just give up on the merge
+	 * if OOM prevents us from merging successfully.
+	 */
+	if (start == vma->vm_start && end == vma->vm_end)
+		give_up_on_oom = true;
 
 	/* Reset ptes for the whole vma range if wr-protected */
 	if (userfaultfd_wp(vma))
@@ -1905,7 +1917,7 @@ struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi,
 
 	ret = vma_modify_flags_uffd(vmi, prev, vma, start, end,
 				    vma->vm_flags & ~__VM_UFFD_FLAGS,
-				    NULL_VM_UFFD_CTX);
+				    NULL_VM_UFFD_CTX, give_up_on_oom);
 
 	/*
 	 * In the vma_merge() successful mprotect-like case 8:
@@ -1956,7 +1968,8 @@ int userfaultfd_register_range(struct userfaultfd_ctx *ctx,
 		new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags;
 		vma = vma_modify_flags_uffd(&vmi, prev, vma, start, vma_end,
 					    new_flags,
-					    (struct vm_userfaultfd_ctx){ctx});
+					    (struct vm_userfaultfd_ctx){ctx},
+					    /* give_up_on_oom = */false);
 		if (IS_ERR(vma))
 			return PTR_ERR(vma);