linux-kernel - Re: [PATCH RESEND 2/2] tracing: syscall_regfunc() should not skip kernel threads

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Message-ID: <20140410155554.44f88536@gandalf.local.home>
Date:	Thu, 10 Apr 2014 15:55:54 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>
Subject: Re: [PATCH RESEND 2/2] tracing: syscall_regfunc() should not skip
 kernel threads

On Thu, 10 Apr 2014 21:38:20 +0200
Oleg Nesterov <oleg@...hat.com> wrote:

> I _think_ that the kernel thread can only return from "call *%rbx" if
> it is no longer a kernel thread, iow, do_execve() was called.

Ah right. But only in special cases.

Actually, it only returns if the function in kernel_thread() returns,
and in the case of ____call_usermodehelper, it does an exec and
returns on success. But if it fails, it needs to call do_exit().

Thus, it's not sufficient to just say "only if do_execve is called" but
to say, if the handler that is called is only allowed to return iff it
did a execve first and succeeded.

-- Steve
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