linux-kernel - Re: [PATCH] debugobjects: insulate non-fixup logic related to static obj from fixup callbacks

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Message-ID: <20160507124716.GM3593@linux.vnet.ibm.com>
Date:	Sat, 7 May 2016 05:47:16 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"Du, Changbin" <changbin.du@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	josh@...htriplett.org, Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	jiangshanlai@...il.com, John Stultz <john.stultz@...aro.org>,
	Tejun Heo <tj@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] debugobjects: insulate non-fixup logic related to static
 obj from fixup callbacks

On Sat, May 07, 2016 at 10:26:28AM +0200, Thomas Gleixner wrote:
> On Sat, 7 May 2016, changbin.du@...el.com wrote:
> 
> Can you please fix your mail client. Every mail you send has:
> 
> Cc: .....
>     "Du, Changbin" <changbin.du@...el.com>,
>     Du
> 
> And that stray 'Du' is just broken.
> 
> > At last, I have a concern about the fixups that can it change the
> > object which is in incorrect state on fixup? Because the 'addr' may
> > not point to any valid object if a non-static object is not tracked.
> > Then Change such object can overwrite someone's memory and cause
> > unexpected behaviour. For example, the timer_fixup_activate bind
> > timer to function stub_timer.
> 
> Well, you have the choice of:
> 
>  1) Leave the object uninitialized and watch the resulting explosion
> 
>  2) Assume that the pointer is a valid object and initialize it     
> 
> The latter has been chosen as the lesser of two evils.
> 
> >  		raw_spin_unlock_irqrestore(&db->lock, flags);
> >  		/*
> > -		 * Maybe the object is static.  Let the type specific
> > +		 * Maybe the object is static. Let the type specific
> >  		 * code decide what to do.
> 
> Instead of doing white space changes you really want to explain the logic
> here.
> 
> >  		 */
> > -		if (debug_object_fixup(descr->fixup_assert_init, addr,
> > -				       ODEBUG_STATE_NOTAVAILABLE))
> > +		if (descr->is_static_object && descr->is_static_object(addr)) {
> > +			/* Make sure that it is tracked in the object tracker */
> > +			debug_object_init(addr, descr);
> > +		} else {
> >  			debug_print_object(&o, "assert_init");
> > +			debug_object_fixup(descr->fixup_assert_init, addr,
> > +					   ODEBUG_STATE_NOTAVAILABLE);
> > +		}
> >  		return;
> >  	}
> 
> Other than the missing comment this looks good.

The transformation to the RCU code looks fine.  So given changes so
that Thomas is good with the overall change, I am good with it from an
RCU perspective.

							Thanx, Paul