Re: [PATCH 1/2] wait/ptrace: always assume __WALL if the child is traced

[Oleg Nesterov <oleg@redhat.com>]

On 10/28, Pedro Alves wrote:
>
> On 10/28/2015 04:11 PM, Oleg Nesterov wrote:
> > On 10/26, Pedro Alves wrote:
> >>
> >> (Also, in the original test case, if the child gets/raises a signal or execs
> >> before exiting, the bash/init/whatever process won't be issuing PTRACE_CONT,
> >> and the child will thus end up stuck (though should be SIGKILLable,
> >
> > Oh, but if it is killable everything is fine. How does this differ from the
> > case when, say, you jusr reparent to init and do kill(getpid(), SIGSTOP) ?
>
> The difference is that if the child called PTRACE_TRACEME, then it goes
> to ptrace-stop instead and no amount of SIGCONT unstucks it -- the only way
> out is force killing.  I agree it's not a major issue as there's a way out
> (and thus made it a parens), but I wouldn't call it nice either.

IOW, the difference is that it is TASK_TRACED, not TASK_STOPPED. I agree,
this is not nice. But this is not nice simply because PTRACE_TRACEME is
not nice.

> >> All this because PTRACE_TRACEME is broken by design
> >
> > Heh. I agree. But we can't fix it now.
>
> Perhaps the man page could document it as deprecated, suggesting
> PTRACE_ATTACH/PTRACE_SEIZE instead?

I don't know. but I won't mind if you mark PTRACE_ATTACH as deprecated
too ;) PTRACE_SEIZE can be used instead and it doesn't abuse SIGSTOP.

Oleg.