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    Subject[patch] pidhash-2.5.38-A0

    the attached patch removes the cmpxchg from the PID allocator and replaces
    it with a spinlock. This spinlock is hit only a couple of times per
    bootup, so it's not a performance issue.

    Ingo

    --- linux/kernel/pid.c.orig Wed Sep 25 10:36:13 2002
    +++ linux/kernel/pid.c Wed Sep 25 10:38:55 2002
    @@ -53,6 +53,8 @@

    static pidmap_t *map_limit = pidmap_array + PIDMAP_ENTRIES;

    +static spinlock_t pidmap_lock __cacheline_aligned_in_smp = SPIN_LOCK_UNLOCKED;
    +
    inline void free_pidmap(int pid)
    {
    pidmap_t *map = pidmap_array + pid / BITS_PER_PAGE;
    @@ -77,8 +79,13 @@
    * Free the page if someone raced with us
    * installing it:
    */
    - if (cmpxchg(&map->page, NULL, (void *) page))
    + spin_lock(&pidmap_lock);
    + if (map->page)
    free_page(page);
    + else
    + map->page = (void *)page;
    + spin_unlock(&pidmap_lock);
    +
    if (!map->page)
    break;
    }
    -
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