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

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Date:	Fri, 27 Mar 2009 15:34:35 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Markus Metzger <markus.t.metzger@...el.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, tglx@...utronix.de,
	hpa@...or.com, markus.t.metzger@...il.com, roland@...hat.com,
	eranian@...glemail.com, juan.villacis@...el.com,
	ak@...ux.jf.intel.com
Subject: Re: [patch 3/14] x86, ptrace, bts: stop bts tracing early in
	do_exit

On 03/27, Markus Metzger wrote:
>
> +static void ptrace_bts_exit(void)
> +{
> +	if (unlikely(!list_empty(&current->ptraced)))
> +		ptrace_bts_exit_tracer();
> +
> +	if (unlikely(current->bts))
> +		ptrace_bts_exit_tracee();
> +}

Could you explain why do we need ptrace_bts_exit_tracee() ?

If current is traced, the tracer should do ptrace_bts_release()
eventually, no?

And if we really need to do ptrace_bts_exit_tracee(), then
"if (unlikely(current->bts))" check is racy. The tracer
can do PTRACE_BTS_CONFIG right after the check.

Oleg.

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