linux-kernel - Re: [PATCH] Make PTRACE_SEIZE set ptrace options specified in data parameter

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Date:	Wed, 7 Sep 2011 23:40:34 +0200
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>, Tejun Heo <tj@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Make PTRACE_SEIZE set ptrace options specified in data parameter

On Wednesday 07 September 2011 19:02, Oleg Nesterov wrote:
> >  	retval = -EIO;
> > -	if (seize && !(flags & PTRACE_SEIZE_DEVEL))
> > -		goto out;
> > +	if (seize) {
> > +		if ((flags & ~(long)PTRACE_O_MASK) != PTRACE_SEIZE_DEVEL)
> > +			goto out;
> > +		flags &= ~PTRACE_SEIZE_DEVEL;
> > +	} else
> > +		flags = 0;
> 
> Personally I do not care, but this is against the coding-style rules. This
> should be
> 
> 	} else {
> 		flags = 0;
> 	}

Ok


> > @@ -263,7 +267,7 @@ static int ptrace_attach(struct task_struct *task, long request,
> >  	if (task->ptrace)
> >  		goto unlock_tasklist;
> >
> > -	task->ptrace = PT_PTRACED;
> > +	task->ptrace = PT_PTRACED | (flags << PT_OPT_FLAG_SHIFT);
> >  	if (seize)
> >  		task->ptrace |= PT_SEIZED;
> 
> Hmm. Tejun, Denys, this doesn't look exactly right.
> 
> I already thought about this before, but somehow I convinced myself
> this is fine.
> 
> I think we should set both PT_PTRACED | PT_SEIZED "atomically", at
> once. Otherwise, say, the tracee can do do_jobctl_trap() in between,
> no? Nothing really bad can happen, but we shouldn't lose EVENT_STOP
> code.
> 
> IOW, I think we need the small fix before this patch.

I think the best is to just do one and only assignment to task->ptrace.
Even before patch, we can touch it three times...

Sending patch v2...

-- 
vda
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