Re: [PATCHSET ptrace] ptrace: implement PTRACE_SEIZE/INTERRUPT andgroup stop notification, take#4

From: Oleg Nesterov
Date: Fri Jun 03 2011 - 11:48:48 EST

On 06/03, Denys Vlasenko wrote:
> On Friday 03 June 2011 03:24, Tejun Heo wrote:
> >
> > Anyways, let's think about that, but SIGSTOP on clone is closely
> > linked to why SEIZE is used in the first place and I currently lean
> > toward tying it to SEIZE.
> Ok.
> SIGSTOP on clone is less problematic because in practice it's
> rather hard to send a real SIGSTOP to a thread which is _just_ created.
> So the race window is mostly theoretical

It is not. The new child can dequeue a signal which was sent to the
process (thread group). How the tracer can distinguish? Also, SIGSTOP
can be sent to pgrp and the new tracee can be forked.

I think that SEIZE should never send SIGSTOP on auto-attach, without
any options.


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