linux-kernel - Re: [PATCH] Don't apply for write lock on tasklist_lock if parent doesn't ptrace other processes

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Message-Id: <20100721222529.EFBAA400B6@magilla.sf.frob.com>
Date:	Wed, 21 Jul 2010 15:25:29 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>, andi.kleen@...el.com,
	Oleg Nesterov <oleg@...hat.com>, stable@...nel.org
Subject: Re: [PATCH] Don't apply for write lock on tasklist_lock if parent
 doesn't ptrace other processes

> > @@ -331,6 +331,9 @@ void exit_ptrace(struct task_struct *tra
> >  	struct task_struct *p, *n;
> >  	LIST_HEAD(ptrace_dead);
> >  
> > +	if (list_empty(&tracer->ptraced))
> > +		return;
> > +
> >  	write_lock_irq(&tasklist_lock);
> >  	list_for_each_entry_safe(p, n, &tracer->ptraced, ptrace_entry) {
> >  		if (__ptrace_detach(tracer, p))

I think we may have tried that before.  Oleg can tell us if it's really
safe vs a race with PTRACE_TRACEME or something like that.


Thanks,
Roland
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