From b6d2c4475d5abc05dd009575b90556bdd3c78ad0 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Niklas=20Hamb=C3=BCchen?= <mail@nh2.me>
Date: Thu, 8 Aug 2019 22:02:27 +0200
Subject: [PATCH] malloc: Fix missing accounting of top chunk in malloc_info
 [BZ #24026]

Fixes `<total type="rest" size="..."> incorrectly showing as 0 most
of the time.

The rest value being wrong is significant because to compute the
actual amount of memory handed out via malloc, the user must subtract
it from <system type="current" size="...">. That result being wrong
makes investigating memory fragmentation issues like
<https://bugzilla.redhat.com/show_bug.cgi?id=843478> close to
impossible.

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 343d89f..0e65d63 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -5406,6 +5406,12 @@ __malloc_info (int options, FILE *fp)
 
       __libc_lock_lock (ar_ptr->mutex);
 
+      /* Account for top chunk.  The top-most available chunk is
+	 treated specially and is never in any bin. See "initial_top"
+	 comments.  */
+      avail = chunksize (ar_ptr->top);
+      nblocks = 1;  /* Top always exists.  */
+
       for (size_t i = 0; i < NFASTBINS; ++i)
 	{
 	  mchunkptr p = fastbin (ar_ptr, i);
-- 
2.9.3