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Date: Thu, 7 May 2009 01:30:27 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Andrew Morton <akpm@linux-foundation.org>,
       Chris Wright <chrisw@sous-sol.org>, Roland McGrath <roland@redhat.com>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] ptrace: cleanup check/set of PT_PTRACED during
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Message-ID: <20090506233027.GB3756@redhat.com>
References: <20090505224727.GA958@redhat.com> <20090506074421.GE17457@elte.hu>
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On 05/06, Ingo Molnar wrote:
>
> * Oleg Nesterov <oleg@redhat.com> wrote:
>
> > ptrace_attach() and ptrace_traceme() are the last functions which 
> > look as if the untraced task can have task->ptrace != 0, this must 
> > not be possible. Change the code to just check ->ptrace != 0 and 
> > s/|=/=/ to set PT_PTRACED.
> >
> > Also, a couple of trivial whitespace cleanups in ptrace_attach().
> >
> > And move ptrace_traceme() up near ptrace_attach() to keep them 
> > close to each other.
>
> btw., while at it, please also fix the typos in 
> include/linux/ptrace.h's PT_* flags section:
>
> /*
>  * Ptrace flags
>  *
>  * The owner ship rules for task->ptrace which holds the ptrace
>  * flags is simple.  When a task is running it owns it's task->ptrace
>  * flags.  When the a task is stopped the ptracer owns task->ptrace.
>  */
>
> s/owner ship/ownership
> s/it's/its

Yes, thanks.

We should change this comment anyway, because it is not right.

The only case when a task owns (iow, can change it safely) its ->ptrace
is: it is running _and_ traced. I think this is what the comment tried
to say.

But this doesn't really matter, because afaics the correct comment
should say: the task should never touch its ->ptrace, ptracer always
owns it.

There is only one exception afaics, de_thread() or do_wait() can call
release_task()->ptrace_unlink() and clear ->ptrace on behalve of
another (not ptracer) task.

Roland, what do you think?

Oleg.