Re: [PATCH 10/16] ptrace: clean transitions between TASK_STOPPEDand TRACED

[Oleg Nesterov]

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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