File malloc-Prevent-arena-free_list-from-turning-cyc... of Package glibc

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File malloc-Prevent-arena-free_list-from-turning-cyclic-B.patch of Package glibc

2015-10-28  Florian Weimer  <fweimer@redhat.com>

[BZ# 19048]
	* malloc/malloc.c (struct malloc_state): Update comment.  Add
	attached_threads member.
	(main_arena): Initialize attached_threads.
	* malloc/arena.c (list_lock): Update comment.
	(ptmalloc_lock_all, ptmalloc_unlock_all): Likewise.
	(ptmalloc_unlock_all2): Reinitialize arena reference counts.
	(deattach_arena): New function.
	(_int_new_arena): Initialize arena reference count and deattach
	replaced arena.
	(get_free_list, reused_arena): Update reference count and deattach
	replaced arena.
	(arena_thread_freeres): Update arena reference count and only put
	unreferenced arenas on the free list.

Index: glibc-2.19/malloc/arena.c
===================================================================
--- glibc-2.19.orig/malloc/arena.c
+++ glibc-2.19/malloc/arena.c
@@ -297,12 +297,19 @@ ptmalloc_unlock_all2 (void)
   tsd_setspecific (arena_key, save_arena);
   __malloc_hook = save_malloc_hook;
   __free_hook = save_free_hook;
+
+  /* Push all arenas to the free list, except save_arena, which is
+     attached to the current thread.  */
+  if (save_arena != NULL)
+    ((mstate) save_arena)->attached_threads = 1;
   free_list = NULL;
   for (ar_ptr = &main_arena;; )
     {
       mutex_init (&ar_ptr->mutex);
       if (ar_ptr != save_arena)
         {
+	  /* This arena is no longer attached to any thread.  */
+	  ar_ptr->attached_threads = 0;
           ar_ptr->next_free = free_list;
           free_list = ar_ptr;
         }
@@ -743,6 +750,22 @@ heap_trim (heap_info *heap, size_t pad)
 
 /* Create a new arena with initial size "size".  */
 
+/* If REPLACED_ARENA is not NULL, detach it from this thread.  Must be
+   called while list_lock is held.  */
+static void
+detach_arena (mstate replaced_arena)
+{
+  if (replaced_arena != NULL)
+    {
+      assert (replaced_arena->attached_threads > 0);
+      /* The current implementation only detaches from main_arena in
+	 case of allocation failure.  This means that it is likely not
+	 beneficial to put the arena on free_list even if the
+	 reference count reaches zero.  */
+      --replaced_arena->attached_threads;
+    }
+}
+
 static mstate
 _int_new_arena (size_t size)
 {
@@ -764,6 +787,7 @@ _int_new_arena (size_t size)
     }
   a = h->ar_ptr = (mstate) (h + 1);
   malloc_init_state (a);
+  a->attached_threads = 1;
   /*a->next = NULL;*/
   a->system_mem = a->max_system_mem = h->size;
   arena_mem += h->size;
@@ -777,12 +801,16 @@ _int_new_arena (size_t size)
   set_head (top (a), (((char *) h + h->size) - ptr) | PREV_INUSE);
 
   LIBC_PROBE (memory_arena_new, 2, a, size);
+  mstate replaced_arena;
+  arena_lookup (replaced_arena);
   tsd_setspecific (arena_key, (void *) a);
   mutex_init (&a->mutex);
   (void) mutex_lock (&a->mutex);
 
   (void) mutex_lock (&list_lock);
 
+  detach_arena (replaced_arena);
+
   /* Add the new arena to the global list.  */
   a->next = main_arena.next;
   atomic_write_barrier ();
@@ -799,13 +827,24 @@ _int_new_arena (size_t size)
 static mstate
 get_free_list (void)
 {
+  mstate replaced_arena;
+  arena_lookup (replaced_arena);
   mstate result = free_list;
   if (result != NULL)
     {
       (void) mutex_lock (&list_lock);
       result = free_list;
       if (result != NULL)
-        free_list = result->next_free;
+	{
+	  free_list = result->next_free;
+
+	  /* Arenas on the free list are not attached to any thread.  */
+	  assert (result->attached_threads == 0);
+	  /* But the arena will now be attached to this thread.  */
+	  result->attached_threads = 1;
+
+	  detach_arena (replaced_arena);
+	}
       (void) mutex_unlock (&list_lock);
 
       if (result != NULL)
@@ -865,6 +904,15 @@ reused_arena (mstate avoid_arena)
   (void) mutex_lock (&result->mutex);
 
 out:
+  {
+    mstate replaced_arena;
+    arena_lookup (replaced_arena);
+    (void) mutex_lock (&list_lock);
+    detach_arena (replaced_arena);
+    ++result->attached_threads;
+    (void) mutex_unlock (&list_lock);
+  }
+
   LIBC_PROBE (memory_arena_reuse, 2, result, avoid_arena);
   tsd_setspecific (arena_key, (void *) result);
   THREAD_STAT (++(result->stat_lock_loop));
@@ -959,8 +1007,14 @@ arena_thread_freeres (void)
   if (a != NULL)
     {
       (void) mutex_lock (&list_lock);
-      a->next_free = free_list;
-      free_list = a;
+      /* If this was the last attached thread for this arena, put the
+	 arena on the free list.  */
+      assert (a->attached_threads > 0);
+      if (--a->attached_threads == 0)
+	{
+	  a->next_free = free_list;
+	  free_list = a;
+	}
       (void) mutex_unlock (&list_lock);
     }
 }
Index: glibc-2.19/malloc/malloc.c
===================================================================
--- glibc-2.19.orig/malloc/malloc.c
+++ glibc-2.19/malloc/malloc.c
@@ -1706,9 +1706,15 @@ struct malloc_state
   /* Linked list */
   struct malloc_state *next;
 
-  /* Linked list for free arenas.  */
+  /* Linked list for free arenas.  Access to this field is serialized
+     by list_lock in arena.c.  */
   struct malloc_state *next_free;
 
+  /* Number of threads attached to this arena.  0 if the arena is on
+     the free list.  Access to this field is serialized by list_lock
+     in arena.c.  */
+  INTERNAL_SIZE_T attached_threads;
+
   /* Memory allocated from the system in this arena.  */
   INTERNAL_SIZE_T system_mem;
   INTERNAL_SIZE_T max_system_mem;
@@ -1752,7 +1758,8 @@ struct malloc_par
 static struct malloc_state main_arena =
 {
   .mutex = MUTEX_INITIALIZER,
-  .next = &main_arena
+  .next = &main_arena,
+  .attached_threads = 1
 };
 
 /* There is only one instance of the malloc parameters.  */

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