linux-kernel - Re: [PATCH 2/2] introduce ptrace

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Date:	Thu,  6 Mar 2008 00:09:02 -0800 (PST)
From:	Roland McGrath <roland@...hat.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] introduce ptrace_reparented() helper

> I am planning to do some changes in forget_original_parent (fix 2 very
> old minor bugs and _perhaps_ add some improvement). I hit the minor but
> nasty problem: this open coded __ptrace_unlink() in reparent_thread().
> _This_ is the actual reason for this patch.
> 
> So. Would you object if I do
> 
> 	--- kernel/ptrace.c	2008-03-03 17:01:06.000000000 +0300
> 	+++ kernel/ptrace.c	2008-03-05 20:22:44.801142777 +0300
> 	@@ -67,11 +67,12 @@ void ptrace_untrace(struct task_struct *
> 	  * remove it from the ptrace list.
> 	  *
> 	  * Must be called with the tasklist lock write-held.
> 	+ *
> 	+ * Either the caller is ptracer, or the caller is ->real_parent
> 	+ * and the child is not traced.
> 	  */
> 	 void __ptrace_unlink(struct task_struct *child)
> 	 {
> 	-	BUG_ON(!child->ptrace);
> 	-
> 		child->ptrace = 0;
> 		if (ptrace_reparented(child)) {
> 			list_del_init(&child->ptrace_list);
> 
> ?

That seems ok.  The duplication of magic in reparent_thread is indeed bad.
I don't think this BUG_ON is buying us much if we haven't hit it in a long
time.


Thanks,
Roland
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