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    SubjectRe: do_syslog/__down_trylock lockup in current BK

    the attached patch fixes one bug in the way we did zap_thread() - but this
    alone does not fix the lockup.

    the bug was that list_for_each_safe() is not 'safe enough' - zap_thread()
    drops the tasklist lock at which point anything might happen to the child
    list.

    the lockup is likely in the while loop - ie. zap_thread() not actually
    reparenting a thread and thus causing an infinite loop - is that possible?

    Ingo

    --- linux/kernel/exit.c.orig Mon Sep 9 21:59:24 2002
    +++ linux/kernel/exit.c Mon Sep 9 22:24:41 2002
    @@ -493,7 +493,6 @@
    static void exit_notify(void)
    {
    struct task_struct *t;
    - struct list_head *_p, *_n;

    forget_original_parent(current);
    /*
    @@ -554,17 +553,16 @@
    do_notify_parent(current, current->exit_signal);

    zap_again:
    - list_for_each_safe(_p, _n, &current->children)
    - zap_thread(list_entry(_p,struct task_struct,sibling), current, 0);
    - list_for_each_safe(_p, _n, &current->ptrace_children)
    - zap_thread(list_entry(_p,struct task_struct,ptrace_list), current, 1);
    + while (!list_empty(&current->children))
    + zap_thread(list_entry(current->children.next,struct task_struct,sibling), current, 0);
    + while (!list_empty(&current->ptrace_children))
    + zap_thread(list_entry(current->ptrace_children.next,struct task_struct,sibling), current, 0);
    /*
    * zap_thread might drop the tasklist lock, thus we could
    * have new children queued back from the ptrace list into the
    * child list:
    */
    - if (unlikely(!list_empty(&current->children) ||
    - !list_empty(&current->ptrace_children)))
    + if (unlikely(!list_empty(&current->children)))
    goto zap_again;
    /*
    * No need to unlock IRQs, we'll schedule() immediately
    -
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