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/ChangeLog b/ChangeLog
index 760698b4409224f6e176e063a1b830c914eadda3..d09461458923b1c6e83b8a4ceac9e62e5f551fe0 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2019-08-08  Niklas Hambüchen  <mail@nh2.me>
+           Carlos O'Donell  <carlos@redhat.com>
+
+       [BZ #24026]
+       * malloc/malloc.c (__malloc_info): Account for top chunk.
+
 2019-08-07  Joseph Myers  <joseph@codesourcery.com>
 
        * sysdeps/unix/sysv/linux/bits/fcntl-linux.h [__USE_GNU]

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 343d89f4893e33b95e7648460c4cb7fd6ff382ab..0e65d636cdddcf07380dd27c5b750a351ecc3786 100644 (file)
--- 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);