linux-kernel - Re: [PATCH 08/12] add trace events for each syscall entry/exit

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Date:	Wed, 26 Aug 2009 18:14:52 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>,
	Jason Baron <jbaron@...hat.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, laijs@...fujitsu.com, peterz@...radead.org,
	mathieu.desnoyers@...ymtl.ca, jiayingz@...gle.com,
	mbligh@...gle.com, lizf@...fujitsu.com,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH 08/12] add trace events for each syscall entry/exit

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.


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