mm/vmalloc: make sure to dump unpurged areas in /proc/vmallocinfo

If last va found in vmap_area_list does not have a vm pointer,
vmallocinfo.s_show() returns 0, and show_purge_info() is not called as
it should.

Link: https://lkml.kernel.org/r/20211001170815.73321-1-eric.dumazet@gmail.com
Fixes: dd3b8353 ("mm/vmalloc: do not keep unpurged areas in the busy tree")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Pengfei Li <lpf.vector@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmalloc.c

@@ -3913,7 +3913,7 @@ static int s_show(struct seq_file *m, void *p)
 			(void *)va->va_start, (void *)va->va_end,
 			va->va_end - va->va_start);
 
-		return 0;
+		goto final;
 	}
 
 	v = va->vm;
@@ -3954,6 +3954,7 @@ static int s_show(struct seq_file *m, void *p)
 	/*
 	 * As a final step, dump "unpurged" areas.
 	 */
+final:
 	if (list_is_last(&va->list, &vmap_area_list))
 		show_purge_info(m);