linux-kernel - Re: [patch 3/14] x86, ptrace, bts: stop bts tracing early in do

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Message-ID: <49D0A29E.2040406@linux.intel.com>
Date:	Mon, 30 Mar 2009 12:44:46 +0200
From:	Andi Kleen <ak@...ux.intel.com>
To:	"Metzger, Markus T" <markus.t.metzger@...el.com>
CC:	Oleg Nesterov <oleg@...hat.com>,
	Markus Metzger <markus.t.metzger@...glemail.com>,
	Ingo Molnar <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"hpa@...or.com" <hpa@...or.com>,
	"roland@...hat.com" <roland@...hat.com>,
	"eranian@...glemail.com" <eranian@...glemail.com>,
	"Villacis, Juan" <juan.villacis@...el.com>,
	"ak@...ux.jf.intel.com" <ak@...ux.jf.intel.com>
Subject: Re: [patch 3/14] x86, ptrace, bts: stop bts tracing early in	do_exit


> 
>>> ds_release_bts(struct bts_tracer *tracer)
>>> {
>>> 	struct task_struct *task =
>>> 		tracer->ds.context->task;
>>>
>>> 	do {
>>> 		set_task_state(task, TASK_UNINTERRUPTIBLE);
>> Oh, this is not right,
> 
> Agreed.
> 
> I wonder if it is ever safe to change another task's state.
> There's a lot of code that sets the task state seemingly
> unprotected - but always for current.

It should be safe when you can guarantee that the other task is stopped
(as in ptrace) and you protect against yourself (only a single
external writer)

-Andi
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