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

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Message-ID: <20140410092842.1f9a8760@gandalf.local.home>
Date:	Thu, 10 Apr 2014 09:28:42 -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>
Subject: Re: [PATCH RESEND 2/2] tracing: syscall_regfunc() should not skip
 kernel threads

On Wed, 9 Apr 2014 19:06:16 +0200
Oleg Nesterov <oleg@...hat.com> wrote:

> syscall_regfunc() ignores the kernel thread because "it has
> no effect", see cc3b13c1 "Don't trace kernel thread syscalls".
> 
> However, this means that a user-space task spawned by
> call_usermodehelper() won't report the system calls if
> kernel_execve() is called when sys_tracepoint_refcount != 0.

What about doing the set there? That is, we could add a check in the
call_userspacehelper() just before it does the do_execve, that if
sys_tracepoint_refcount is set, we set the TIF flag.


-- Steve

> 
> Remove this check. Hopefully the unnecessary report from
> ret_from_fork path mentioned by cc3b13c1 is fine. In fact
> "this is the only case" is not true. Say, kernel_execve()
> itself does "int 80" on X86_32. Hopefully fine too.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/tracepoint.c |    4 +---
>  1 files changed, 1 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index a16754b..4e1e4ca 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -737,9 +737,7 @@ void syscall_regfunc(void)
>  	if (!sys_tracepoint_refcount) {
>  		read_lock(&tasklist_lock);
>  		do_each_thread(g, t) {
> -			/* Skip kernel threads. */
> -			if (!(t->flags & PF_KTHREAD))
> -				set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
> +			set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
>  		} while_each_thread(g, t);
>  		read_unlock(&tasklist_lock);
>  	}

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