linux-kernel - Re: [patch 1/5] Debugobjects transition check

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Date:	Wed, 31 Mar 2010 15:51:27 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
cc:	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	laijs@...fujitsu.com, dipankar@...ibm.com, josh@...htriplett.org,
	dvhltc@...ibm.com, niv@...ibm.com, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, adobriyan@...il.com,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [patch 1/5] Debugobjects transition check

On Wed, 31 Mar 2010, Mathieu Desnoyers wrote:

> * Thomas Gleixner (tglx@...utronix.de) wrote:
> > On Mon, 29 Mar 2010, Mathieu Desnoyers wrote:
> > 
> > > Implement a basic state machine checker in the debugobjects.
> > 
> > Can you please add some real explanation how that checker works and
> > why we want to have it ?
> 
> We can add this to the changelog. Is it worth it to create a Documentation file
> for it ?

I meant the changelog. The "Implement ...." line was not really helpful :)
 
> 
> This state machine checker detects races and inconsistencies within the "active"
> life of a debugobject. The checker only keeps track of the current state; all
> the state machine logic is kept at the object instance level.
> 
> The checker works by adding a supplementary "unsigned int astate" field to the
> debug_obj structure. It keeps track of the current "active state" of the object.
> 
> The only constraints that are imposed on the states by the debugobjects system
> is that:
> 
> - activation of an object sets the current active state to 0,
> - deactivation of an object expects the current active state to be 0.
> 
> For the rest of the states, the state mapping is determined by the specific
> object instance. Therefore, the logic keeping track of the state machine is
> within the specialized instance, without any need to know about it at the
> debugobject level.
> 
> The current object active state is changed by calling:
> 
> debug_object_active_state(addr, descr, expect, next)
> 
> where "expect" is the expected state and "next" is the next state to move to if
> the expected state is found. A warning is generated if the expected is not
> found.

Does it only warn or is there a callback to fixup things as well ?

Thanks,

	tglx
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