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Date: Wed, 26 Aug 2009 15:53:35 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>,
       Hendrik Brueckner <brueckner@linux.vnet.ibm.com>,
       Jason Baron <jbaron@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
       Ingo Molnar <mingo@elte.hu>, Lai Jiangshan <laijs@cn.fujitsu.com>,
       Peter Zijlstra <peterz@infradead.org>,
       Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>, jiayingz@google.com,
       mbligh@google.com, lizf@cn.fujitsu.com,
       Martin Schwidefsky <schwidefsky@de.ibm.com>
Subject: Re: [PATCH 08/12] add trace events for each syscall entry/exit
Message-ID: <20090826135331.GF6009@nowhere>
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On Wed, Aug 26, 2009 at 09:48:48AM -0400, Steven Rostedt wrote:
> 
> On Wed, 26 Aug 2009, Frederic Weisbecker wrote:
> > > 
> > > That won't always work as pointed out in the other example:
> > > - Process doing sys_init_module then scheduled away
> > > - User enables syscall tracing -> TIF_SYSCALL_FTRACE gets set
> > > - init function of the module gets called and is doing kernel_thread()
> > >   (old API) -> kernel thread inherits TIF_SYSCALL_FTRACE.
> > > 
> > > I don't think that's what you want. You might want to clear the flag for
> > > new processes during fork (only for kernel threads I would guess).
> > > 
> > > At least the current patch leaves a hole.
> > 
> > 
> > Ah, there are callsites that use kernel_thread() directly?
> > Does it means that t->mm could be non NULL for such resulting
> > kernel threads, in that case it would be hard to hook on
> > do_fork() to check that.
> 
> All kernel threads have a NULL t->mm. Since do_fork is called by kthreadd 
> and not by kthread_create, the caller of do_fork will also have a
> t->mm = NULL.
> 
> -- Steve
> 

Yeah, that's the case with kthread_create() creation fashion,
but what if you create a kernel thread using the low level
kernel_thread() directly (ie: without relaying on kthreadd queue)?

Especially in Heiko example, it seems to be a duplication of user
task.

I wonder what obvious think I'm missing here...