Attachment 8674 Details for Bug 19048 – 0001-Avoid-corruption-of-free_list.patch

[patch] 0001-Avoid-corruption-of-free_list.patch

0001-Avoid-corruption-of-free_list.patch (text/plain), 1.74 KB, created by Paulo Andrade on 2015-10-02 14:33:46 UTC

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Creator: Paulo Andrade

Created: 2015-10-02 14:33:46 UTC

Size: 1.74 KB

patch

obsolete

>From 68dbd2426b738a32324c225a543a12908dafaf43 Mon Sep 17 00:00:00 2001
>From: Paulo Andrade <pcpa@gnu.org>
>Date: Fri, 2 Oct 2015 11:10:04 -0300
>Subject: [PATCH] Avoid corruption of free_list
>
>  When a thread leaves, arena_thread_freeres is called, the malloc
>arena associated with the thread is added to the head of free_list,
>and free_list set to the arena of the exiting thread.
>
>  A common problem can be described as:
>1. thread "t1" uses arena "a"
>2. thread "t2" uses arena "a"
>3. "t1" exit, making:
>	a->next_free = free_list;
>	free_list = a;
>4. "t2" exits, but since free_list == a, it ends with
>   free_list->next_free = free_list;
>
>  When a program has several short lived threads, and most commonly
>when there are more threads than arenas, one arena will end up being
>used by most threads, causing significant contention.
>---
> malloc/arena.c | 22 ++++++++++++++++++++--
> 1 file changed, 20 insertions(+), 2 deletions(-)
>
>diff --git a/malloc/arena.c b/malloc/arena.c
>index b44e307..afe775b 100644
>--- a/malloc/arena.c
>+++ b/malloc/arena.c
>@@ -935,8 +935,26 @@ arena_thread_freeres (void)
>   if (a != NULL)
>     {
>       (void) mutex_lock (&list_lock);
>-      a->next_free = free_list;
>-      free_list = a;
>+      /* Use other arenas before "a".  */
>+      if (a == free_list)
>+	free_list = free_list->next_free;
>+      /* Insert "a" last in free_list.  */
>+      if (free_list != NULL)
>+	{
>+	  mstate b = free_list;
>+	  while (b->next_free != NULL)
>+	    {
>+	      /* Make sure to check if "a" is already in free_list. */
>+	      if (b->next_free == a)
>+		b->next_free = a->next_free;
>+	      else
>+		b = b->next_free;
>+	    }
>+	  b->next_free = a;
>+	}
>+      else
>+	free_list = a;
>+      a->next_free = NULL;
>       (void) mutex_unlock (&list_lock);
>     }
> }
>-- 
>1.8.3.1
>

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