mm/vma: return the exact errno in vms_gather_munmap_vmas()

__split_vma() and mas_store_gfp() returns several types of errno on
failure so don't ignore them in vms_gather_munmap_vmas().  For example,
__split_vma() returns -EINVAL when an unaligned huge page is unmapped. 
This issue is reproduced by ltp memfd_create03 test.

Don't initialise the error variable and assign it when a failure actually
occurs.

[akpm@linux-foundation.org: fix whitespace, per Liam]
Link: https://lkml.kernel.org/r/20240909125621.1994-1-ice_yangxiao@163.com
Fixes: 6898c903 ("mm/vma: extract the gathering of vmas from do_vmi_align_munmap()")
Signed-off-by: Xiao Yang <ice_yangxiao@163.com>
Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202409081536.d283a0fb-oliver.sang@intel.com
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/vma.c

@@ -1171,13 +1171,13 @@ void vms_complete_munmap_vmas(struct vma_munmap_struct *vms,
  * @vms: The vma munmap struct
  * @mas_detach: The maple state tracking the detached tree
  *
- * Return: 0 on success, -EPERM on mseal vmas, -ENOMEM otherwise
+ * Return: 0 on success, error otherwise
  */
 int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
 		struct ma_state *mas_detach)
 {
 	struct vm_area_struct *next = NULL;
-	int error = -ENOMEM;
+	int error;
 
 	/*
 	 * If we need to split any vma, do it now to save pain later.
@@ -1191,8 +1191,10 @@ int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
 		 * its limit temporarily, to help free resources as expected.
 		 */
 		if (vms->end < vms->vma->vm_end &&
-		    vms->vma->vm_mm->map_count >= sysctl_max_map_count)
+		    vms->vma->vm_mm->map_count >= sysctl_max_map_count) {
+			error = -ENOMEM;
 			goto map_count_exceeded;
+		}
 
 		/* Don't bother splitting the VMA if we can't unmap it anyway */
 		if (!can_modify_vma(vms->vma)) {
@@ -1200,7 +1202,8 @@ int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
 			goto start_split_failed;
 		}
 
-		if (__split_vma(vms->vmi, vms->vma, vms->start, 1))
+		error = __split_vma(vms->vmi, vms->vma, vms->start, 1);
+		if (error)
 			goto start_split_failed;
 	}
 	vms->prev = vma_prev(vms->vmi);
@@ -1220,12 +1223,14 @@ int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
 		}
 		/* Does it split the end? */
 		if (next->vm_end > vms->end) {
-			if (__split_vma(vms->vmi, next, vms->end, 0))
+			error = __split_vma(vms->vmi, next, vms->end, 0);
+			if (error)
 				goto end_split_failed;
 		}
 		vma_start_write(next);
 		mas_set(mas_detach, vms->vma_count++);
-		if (mas_store_gfp(mas_detach, next, GFP_KERNEL))
+		error = mas_store_gfp(mas_detach, next, GFP_KERNEL);
+		if (error)
 			goto munmap_gather_failed;
 
 		vma_mark_detached(next, true);
@@ -1255,8 +1260,9 @@ int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
 			 * split, despite we could. This is unlikely enough
 			 * failure that it's not worth optimizing it for.
 			 */
-			if (userfaultfd_unmap_prep(next, vms->start, vms->end,
-						   vms->uf))
+			error = userfaultfd_unmap_prep(next, vms->start,
+						       vms->end, vms->uf);
+			if (error)
 				goto userfaultfd_error;
 		}
 #ifdef CONFIG_DEBUG_VM_MAPLE_TREE