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    SubjectRe: do_syslog/__down_trylock lockup in current BK
    On Mon, Sep 09, 2002 at 10:33:17PM +0200, Ingo Molnar wrote:
    >
    > 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?

    Well, it shouldn't be. forget_original_parent should update
    real_parent for every child on either list, and then zap_thread unlinks
    each child from the current parent and links it to the new real_parent.
    A couple of printks in there should be able to work out if I'm wrong,
    though...

    > @@ -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);

    As Linus points out, typo right there on the last argument.

    --
    Daniel Jacobowitz
    MontaVista Software Debian GNU/Linux Developer
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