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Date: Sat, 14 Oct 2006 03:00:39 +0900
From: Akinobu Mita <akinobu.mita@gmail.com>
To: Andrew Morton <akpm@osdl.org>
Cc: linux-kernel@vger.kernel.org, ak@suse.de, Don Mullis <dwm@meer.net>,
       Valdis.Kletnieks@vt.edu
Subject: Re: [patch 7/7] stacktrace filtering for fault-injection capabilities
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On Thu, Oct 12, 2006 at 02:20:04PM -0700, Andrew Morton wrote:

> I read the documentation but I still don't understand this feature.  What
> does the stacktrace actually do?  It gets stored somewhere and displayed
> later?  What's it all for?

For example someone may want to inject kmalloc()/kmem_cache_alloc()
failures into only e100 module. they want to inject not only direct
kmalloc() call, but also indirect allocation, too.

- e100_poll --> netif_receive_skb --> packet_rcv_spkt --> skb_clone
  --> kmem_cache_alloc

This patch enables to detect function calls like this by stacktrace
and inject failures. The script
Documentaion/fault-injection/failmodule.sh
helps it.

The range of text section of loaded e100 is expected to be
[/sys/module/e100/sections/.text, /sys/module/e100/sections/.exit.text)

So failmodule.sh stores these values into /debug/failslab/address-start
and /debug/failslab/address-end.

> > --- work-fault-inject.orig/lib/Kconfig.debug
> > +++ work-fault-inject/lib/Kconfig.debug
> > @@ -472,6 +472,8 @@ config LKDTM
> >  
> >  config FAULT_INJECTION
> >  	bool
> > +	select STACKTRACE
> > +	select FRAME_POINTER
> >  
> >  config FAILSLAB
> >  	bool "fault-injection capabilitiy for kmalloc"
> > 
> 
> Is the selection of FRAME_POINTER really needed?  The fancy new unwinder
> is supposed to be able to handle frame-pointerless unwinding?

As I wrote in another reply, There are two type of implementation of
this stacktrace filter.

- using STACKTRACE + FRAME_POINTER
- using new unwinder (STACK_UNWIND)

The stacktrace with using new unwinder without FRAME_POINTER is much
slower than STACKTRACE + FRAME_POINTER.