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Date: Wed, 26 Aug 2009 18:14:52 +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>, linux-kernel@vger.kernel.org,
       mingo@elte.hu, laijs@cn.fujitsu.com, peterz@infradead.org,
       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: <20090826161449.GB6304@nowhere>
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On Wed, Aug 26, 2009 at 10:43:01AM -0400, Steven Rostedt wrote:
> 
> On Wed, 26 Aug 2009, Frederic Weisbecker wrote:
> > > 
> > > Oh yes, you are right. kernel threads created with kernel_thread()
> > > have t->mm != NULL if the forking process has an mm too.
> > > 
> > > There are very few callsites left which still use kernel_thread().
> > > (the last one in s390 driver code will be gone after the next
> > > merge window).
> > > 
> > > As far as I can there are only four callsites left
> > > (excluding staging): jffs2 and three in net/bluetooth/*
> > 
> > 
> > In that case, I'd suggest to pick the patch that checks for
> > kernel threads while setting the TIF_FLAGS.
> > 
> > The check for invalid syscall numbers in another patch should be
> > sufficient to not crash.
> > 
> > We might have rare inaccurate result because of the remaining
> > buggy callsites but instead of working around on it, these
> > should be fixed.
> 
> Well, do these (buggy threads) call syscalls?
> 
> -- Steve
> 


That's not exactly what raises bugs because their syscalls
won't be traced. The problem occurs when the freshly created
kernel thread reaches ret_from_fork with its ->mm != NULL

It will take the trace_sys_exit() call and then will be traced
as a normal user thread.