linux-kernel - Re: [PATCH v2 1/2] livepatch: Initialize shadow variables safely by a custom callback

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Message-ID: <20180406223420.icjwcq7vy24tvecu@treble>
Date:   Fri, 6 Apr 2018 17:34:20 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Jiri Kosina <jikos@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Jessica Yu <jeyu@...nel.org>, Nicolai Stange <nstange@...e.de>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] livepatch: Initialize shadow variables safely by
 a custom callback

On Thu, Apr 05, 2018 at 02:23:14PM +0200, Petr Mladek wrote:
> @@ -150,6 +149,23 @@ static void *__klp_shadow_get_or_alloc(void *obj, unsigned long id, void *data,
>  		goto exists;
>  	}
>  
> +	new_shadow->obj = obj;
> +	new_shadow->id = id;
> +
> +	if (ctor) {
> +		int err;
> +
> +		err = ctor(obj, new_shadow->data, ctor_data);
> +		if (err) {
> +			spin_unlock_irqrestore(&klp_shadow_lock, flags);
> +			kfree(new_shadow);
> +			WARN(1,
> +			     "Failed to construct shadow variable <%p, %lx>\n",
> +			     obj, id);
> +			return NULL;
> +		}
> +	}
> +

I'm not sure why a constructor would return an error, though I guess it
doesn't hurt to allow it.

The WARN seems excessive though, IMO.  The constructor itself can warn
(or printk or whatever else) if it thinks its warranted.

Also I think the 'err' variable isn't really needed.

-- 
Josh