linux-kernel - Re: [PATCH v4] livepatch: introduce shadow variable API

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Message-ID: <2fc0160b-d16a-97d3-3ea1-4a787b8afd48@redhat.com>
Date:   Wed, 16 Aug 2017 09:40:44 -0400
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jessica Yu <jeyu@...hat.com>, Jiri Kosina <jikos@...nel.org>,
        Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH v4] livepatch: introduce shadow variable API

On 08/16/2017 08:43 AM, Miroslav Benes wrote:
> 
>> [ ... snip ... ]
> 
> There is a comment above about locking and we do not take the spinlock 
> here. That could surprise someone. So I'd keep only klp_shadow_add() 
> comment, because there it is strictly needed. It depends on the context in 
> all other cases.

Good catch, I think this changed in this last version when I moved some
of the work outside the lock.

> Could you also add a comment above klp_shadow_lock definition about what 
> it aims to protect?
> 

How about "klp_shadow_lock provides exclusive access to the
klp_shadow_hash and the shadow variables it references."  or were
thinking of something more detailed?

>> +	/* Look for <obj, id> again under the lock */
>> +	spin_lock_irqsave(&klp_shadow_lock, flags);
>> +	shadow_data = klp_shadow_get(obj, id);
>> +	if (unlikely(shadow_data)) {
> 
> shadow_data is not needed anywhere, so you could do the same as for the 
> first speculative search and remove shadow_data variable all together.

Ok.

>> [ ... snip ... ]
> 
> Otherwise it looks good. You can add my
> 
> Acked-by: Miroslav Benes <mbenes@...e.cz>
> 
> with those nits fixed.

Thank you for all the suggestions and reviews!

-- Joe