mm/vmalloc.c: avoid bogus -Wmaybe-uninitialized warning

gcc gets confused in pcpu_get_vm_areas() because there are too many
branches that affect whether 'lva' was initialized before it gets used:

  mm/vmalloc.c: In function 'pcpu_get_vm_areas':
  mm/vmalloc.c:991:4: error: 'lva' may be used uninitialized in this function [-Werror=maybe-uninitialized]
      insert_vmap_area_augment(lva, &va->rb_node,
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
       &free_vmap_area_root, &free_vmap_area_list);
       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  mm/vmalloc.c:916:20: note: 'lva' was declared here
    struct vmap_area *lva;
                      ^~~

Add an intialization to NULL, and check whether this has changed before
the first use.

[[email protected]: tweak comments]
Link: http://lkml.kernel.org/r/[email protected]
Fixes: 68ad4a3 ("mm/vmalloc.c: keep track of free blocks for vmap allocation")
Signed-off-by: Arnd Bergmann <[email protected]>
Reviewed-by: Uladzislau Rezki (Sony) <[email protected]>
Cc: Joel Fernandes <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/vmalloc.c

@@ -913,7 +913,7 @@ adjust_va_to_fit_type(struct vmap_area *va,
 	unsigned long nva_start_addr, unsigned long size,
 	enum fit_type type)
 {
-	struct vmap_area *lva;
+	struct vmap_area *lva = NULL;
 
 	if (type == FL_FIT_TYPE) {
 		/*
@@ -972,7 +972,7 @@ adjust_va_to_fit_type(struct vmap_area *va,
 	if (type != FL_FIT_TYPE) {
 		augment_tree_propagate_from(va);
 
-		if (type == NE_FIT_TYPE)
+		if (lva)	/* type == NE_FIT_TYPE */
 			insert_vmap_area_augment(lva, &va->rb_node,
 				&free_vmap_area_root, &free_vmap_area_list);
 	}