linux-kernel - Re: [PATCH v14 07/11] livepatch: Add atomic replace

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Date:   Mon, 17 Dec 2018 16:27:41 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Josh Poimboeuf <jpoimboe@...hat.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 07/11] livepatch: Add atomic replace

On Thu 2018-12-13 16:55:28, Josh Poimboeuf wrote:
> On Thu, Nov 29, 2018 at 10:44:27AM +0100, Petr Mladek wrote:
> > @@ -415,6 +449,124 @@ static struct attribute *klp_patch_attrs[] = {
> >  	NULL
> >  };
> >  
> > +/*
> > + * Dynamically allocated objects and functions.
> > + */
> 
> I don't think this comment is needed.
> 
> > +static void klp_free_object_dynamic(struct klp_object *obj)
> > +{
> > +	kfree(obj->name);
> > +	kfree(obj);
> > +}
> > @@ -456,6 +620,8 @@ static void klp_free_funcs(struct klp_object *obj)
> >  		if (func->kobj_alive) {
> >  			func->kobj_alive = false;
> >  			kobject_put(&func->kobj);
> > +		} else if (func->nop) {
> > +			klp_free_func_nop(func);
> 
> This removes 'func' from the list, so it needs to do a 'safe' list
> iteration.

Good catch!

Well, note that the 'safe' list iterators were added by the very next
patch anyway. This is why I never triggered a problem with this.


> > +void klp_discard_replaced_patches(struct klp_patch *new_patch)
> > +{
> > +	struct klp_patch *old_patch, *tmp_patch;
> > +
> > +	list_for_each_entry_safe(old_patch, tmp_patch, &klp_patches, list) {
> > +		if (old_patch == new_patch)
> > +			return;
> > +
> > +		old_patch->enabled = false;
> > +		klp_unpatch_objects(old_patch);
> > +		klp_free_patch_start(old_patch);
> > +		schedule_work(&old_patch->free_work);
> > +	}
> 
> This doesn't need the "safe" list iteration because it doesn't remove
> the patch from the list.

It does need the 'safe' list. klp_free_patch_start() removes
the patch from the list.


> Side note, it would probably be useful to have a klp_for_each_patch()
> helper.

Will do.

Best Regards,
Petr