linux-kernel - Re: [PATCH v14 03/11] livepatch: Consolidate klp

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Date:   Fri, 14 Dec 2018 08:23:33 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Jiri Kosina <jikos@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
        Jason Baron <jbaron@...mai.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jessica Yu <jeyu@...nel.org>
Subject: Re: [PATCH v14 03/11] livepatch: Consolidate klp_free functions

On Fri, Dec 14, 2018 at 10:32:01AM +0100, Petr Mladek wrote:
> On Thu 2018-12-13 16:10:37, Josh Poimboeuf wrote:
> > On Thu, Nov 29, 2018 at 10:44:23AM +0100, Petr Mladek wrote:
> > > +static void klp_free_funcs(struct klp_object *obj)
> > >  {
> > >  	struct klp_func *func;
> > >  
> > > -	for (func = obj->funcs; func->old_name && func != limit; func++)
> > > -		kobject_put(&func->kobj);
> > > +	klp_for_each_func(obj, func) {
> > > +		/* Might be called from klp_init_patch() error path. */
> > > +		if (func->kobj_alive) {
> > > +			func->kobj_alive = false;
> > > +			kobject_put(&func->kobj);
> > > +		}
> > 
> > Why does it set 'kobj_alive' to false?  The value will never be read
> > again anyway, right?
> 
> You are right. I'll remove it in v15.
> 
> My intention was that it might signalize that the kobject is being
> freed and eventually affect the behavior of sysfs-related callbacks.
> But in reality, it should be handled by some per-patch flag instead
> of a per-object one.
> 
> 
> > Also, the name isn't quite right.  The kobject is technically still
> > alive here, and may even continue to be alive after the kobject_put(),
> > if there's a sysfs reference to it somewhere.
> > 
> > Maybe it should be called something like 'kobj_initialized' instead.
> > Then it doesn't ever need to be set to false -- unless I'm missing
> > something.
> 
> This might cause confusion with kobj.state_initialized. This internal
> kobject flag is set when the reference counter is initialized. But
> it is true even before kobject_add() is called.
> 
> We need a flag that signalizes that kobject_add() succeeded and we
> can and must call kobject_put().
> 
> What about calling it 'kobj_added'?

Sounds good to me.

-- 
Josh