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    SubjectRe: [PATCH 10/16] ptrace: clean transitions between TASK_STOPPED and TRACED
    On 12/22, Tejun Heo wrote:
    >
    > On Wed, Dec 22, 2010 at 12:39:48PM +0100, Oleg Nesterov wrote:
    > >
    > > sys_ptrace() only works for the single thread who did PTRACE_ATTACH,
    > > but do_wait() should work for its sub-threads.
    > >
    > > 1. the tracer knows that the tracee is stopped
    > >
    > > 2. the tracer does ptrace(ATTACH)
    > >
    > > 3. the tracer's sub-thread does do_wait()
    > >
    > > Note! Personally I think we can ignore this "problem", I do not
    > > think it can break anything except some specialized test-case.
    >
    > But if ptrace(ATTACH) doesn't return until the transition is complete
    > when the task is already stopped, the tracer's sub-thread's do_wait()
    > will behave exactly the same. The only difference would be that
    > ptrace(ATTACH) may now block and/or is failed by a signal delivery.
    >
    > How would #3 behave differently if STOPPED -> TRACED transition is
    > guaranteed to be complete by the end of #2?

    Ahhh, sorry. I meant, two threads can do 2. and 3. at the same time.

    But let me repeat, it is not that I think we should worry. I mentioned
    this only because I think it is better to discuss everything we can,
    even the really minor things.

    Oleg.



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