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

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Date:   Thu, 6 Dec 2018 09:23:47 -0500
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Jason Baron <jbaron@...mai.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 12/06/2018 03:15 AM, Petr Mladek wrote:
> On Wed 2018-12-05 14:02:20, Joe Lawrence wrote:
>> On Thu, Nov 29, 2018 at 10:44:23AM +0100, Petr Mladek wrote:
>>> The code for freeing livepatch structures is a bit scattered and tricky:
>>>
>>> [ ... snip ... ]
>>>
>>> +static int klp_init_patch(struct klp_patch *patch)
>>> +{
>>> +	struct klp_object *obj;
>>> +	int ret;
>>> +
>>> +	mutex_lock(&klp_mutex);
>>> +
>>> +	ret = klp_init_patch_before_free(patch);
>>>  	if (ret) {
>>>  		mutex_unlock(&klp_mutex);
>>>  		return ret;
>>>  	}
>>>
>>
>> I believe klp_init_patch_before_free() accumulates more responsibilities
>> later in the patchset, but I'll ask here: does it really need the
>> klp_mutex since it looks to be operating only on the klp_patch, its
>> objects and functions? 
> 
> I do not have a strong opinion about it.
> 
> On one hand, we are manipulating all the structures and should prevent
> any parallel use. On the other hand, the rest of the code will not
> touch the patch until it is added into klp_patches list or until
> the sysfs interface is created.
> 
> If you think that it might cause false expectations and confusions
> then I could move it out of the lock.

I didn't find it confusing, nor is it performance limiting.  I figured I
would point it out in case there was some reason for the mutex that I
had missed.

> Well, in the final version we need to call klp_check_patch_conflict()
> under the mutex.

That's right.

-- Joe