perf hists: Add extra integrity checks to fmt_free()

Make sure the struct perf_hpp_fmt is properly unhooked before we free
it.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Changbin Du <changbin.du@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/20171013083736.15037-3-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/ui/hist.c

@@ -606,6 +606,13 @@ void perf_hpp__append_sort_keys(struct perf_hpp_list *list)
 
 static void fmt_free(struct perf_hpp_fmt *fmt)
 {
+	/*
+	 * At this point fmt should be completely
+	 * unhooked, if not it's a bug.
+	 */
+	BUG_ON(!list_empty(&fmt->list));
+	BUG_ON(!list_empty(&fmt->sort_list));
+
 	if (fmt->free)
 		fmt->free(fmt);
 }