commit a3b473373ee43a292f5ec68a7fda6b9cfb26a9b0

Author: Florian Weimer <fweimer@redhat.com>

Date:   Tue Jun 21 21:29:21 2016 +0200

    malloc: Avoid premature fallback to mmap [BZ #20284]

    Before this change, the while loop in reused_arena which avoids

    returning a corrupt arena would never execute its body if the selected

    arena were not corrupt.  As a result, result == begin after the loop,

    and the function returns NULL, triggering fallback to mmap.

Index: glibc-2.17-c758a686/malloc/arena.c

===================================================================

--- glibc-2.17-c758a686.orig/malloc/arena.c

+++ glibc-2.17-c758a686/malloc/arena.c

@@ -907,14 +907,12 @@ reused_arena (mstate avoid_arena)

     {

       result = result->next;

       if (result == begin)

-	break;

+	/* We looped around the arena list.  We could not find any

+	   arena that was either not corrupted or not the one we

+	   wanted to avoid.  */

+	return NULL;

     }

-  /* We could not find any arena that was either not corrupted or not the one

-     we wanted to avoid.  */

-  if (result == begin || result == avoid_arena)

-    return NULL;

-

   /* No arena available without contention.  Wait for the next in line.  */

   LIBC_PROBE (memory_arena_reuse_wait, 3, &result->mutex, result, avoid_arena);

   (void)mutex_lock(&result->mutex);