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Subject: Re: [PATCH v14 03/11] livepatch: Consolidate klp_free functions
To:     Petr Mladek <pmladek@suse.com>
Cc:     Jiri Kosina <jikos@kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Miroslav Benes <mbenes@suse.cz>,
        Jason Baron <jbaron@akamai.com>,
        Evgenii Shatokhin <eshatokhin@virtuozzo.com>,
        live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
        Jessica Yu <jeyu@kernel.org>
References: <20181129094431.7801-1-pmladek@suse.com>
 <20181129094431.7801-4-pmladek@suse.com>
 <20181205190220.vterzx33opvvijne@redhat.com>
 <20181206081501.jkki7hg4u43fqwth@pathway.suse.cz>
From:   Joe Lawrence <joe.lawrence@redhat.com>
Organization: Red Hat
Message-ID: <d4dcf407-462a-e6bd-7ab5-6d27fbcccb99@redhat.com>
Date:   Thu, 6 Dec 2018 09:23:47 -0500
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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