[Bug malloc/19048] New: Avoid corruption of free_list

["paulo.cesar.pereira.de.andrade at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=19048

            Bug ID: 19048
           Summary: Avoid corruption of free_list
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: malloc
          Assignee: unassigned at sourceware dot org
          Reporter: paulo.cesar.pereira.de.andrade at gmail dot com
  Target Milestone: ---

Created attachment 8666
  --> https://sourceware.org/bugzilla/attachment.cgi?id=8666&action=edit
0001-Avoid-corruption-of-free_list.patch

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.

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