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    SubjectRe: init's children list is long and slows reaping children.

    * Eric W. Biederman <ebiederm@xmission.com> wrote:

    > > on a second thought: the p->children list is needed for the whole
    > > child/parent task tree, which is needed for sys_getppid().
    >
    > Yes, something Oleg said made me realize that.
    >
    > As long as the reparent isn't to complex it isn't required that we
    > have exactly one list .
    >
    > > The question is, does anything require us to reparent to within the
    > > same thread group?
    >
    > I think my head is finally on straight about this question.
    >
    > Currently there is the silly linux specific parent death signal
    > (pdeath_signal). Oleg's memory was a better than mine on this score.
    >
    > However there is no indication that the parent death signal being sent
    > when a thread leader dies is actually correct, or even interesting. It
    > probably should only be sent when getppid changes.
    >
    > So with pdeath_signal fixed that is nothing that requires us to
    > reparent within the same thread group.
    >
    > I'm trying to remember what the story is now. There is a nasty race
    > somewhere with reparenting, a threaded parent setting SIGCHLD to
    > SIGIGN, and non-default signals that results in an zombie that no one
    > can wait for and reap. It requires being reparented twice to trigger.
    >
    > Anyway it is a real mess and if we can remove the stupid multi-headed
    > child lists things would become much simpler and the problem could not
    > occur.
    >
    > Plus the code would become much simpler...
    >
    > utrace appears to have removed the ptrace_children list and the
    > special cases that entailed.

    so ... is anyone pursuing this? This would allow us to make sys_wait4()
    faster and more scalable: no tasklist_lock bouncing for example.

    Ingo
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