linux-kernel - Re: [External] Re: [PATCH v3] livepatch: Don't block removal of patches that are safe to unload

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Message-ID: <f27650d5-5ff5-f954-5eb2-745a7bfc0dcb@bytedance.com>
Date:   Thu, 17 Mar 2022 09:15:22 +0800
From:   Chengming Zhou <zhouchengming@...edance.com>
To:     Petr Mladek <pmladek@...e.com>, Miroslav Benes <mbenes@...e.cz>
Cc:     jpoimboe@...hat.com, jikos@...nel.org, joe.lawrence@...hat.com,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        songmuchun@...edance.com, qirui.001@...edance.com
Subject: Re: [External] Re: [PATCH v3] livepatch: Don't block removal of
 patches that are safe to unload

On 2022/3/16 11:01 下午, Petr Mladek wrote:
> On Wed 2022-03-16 15:48:25, Miroslav Benes wrote:
>> On Sat, 12 Mar 2022, Chengming Zhou wrote:
>>
>>> module_put() is not called for a patch with "forced" flag. It should
>>> block the removal of the livepatch module when the code might still
>>> be in use after forced transition.
>>>
>>> klp_force_transition() currently sets "forced" flag for all patches on
>>> the list.
>>>
>>> In fact, any patch can be safely unloaded when it passed through
>>> the consistency model in KLP_UNPATCHED transition.
>>>
>>> By other words, the "forced" flag must be set only for livepatches
>>
>> s/By/In/
>>
>>> that are being removed. In particular, set the "forced" flag:
>>>
>>>   + only for klp_transition_patch when the transition to KLP_UNPATCHED
>>>     state was forced.
>>>
>>>   + all replaced patches when the transition to KLP_PATCHED state was
>>>     forced and the patch was replacing the existing patches.
>>>
>>> index 5683ac0d2566..7f25a5ae89f6 100644
>>> --- a/kernel/livepatch/transition.c
>>> +++ b/kernel/livepatch/transition.c
>>> @@ -641,6 +641,18 @@ void klp_force_transition(void)
>>>  	for_each_possible_cpu(cpu)
>>>  		klp_update_patch_state(idle_task(cpu));
>>>  
>>> -	klp_for_each_patch(patch)
>>> -		patch->forced = true;
>>> +	/*
>>> +	 * Only need to set forced flag for the transition patch
>>> +	 * when force transition to KLP_UNPATCHED state, but
>>> +	 * have to set forced flag for all replaced patches
>>> +	 * when force atomic replace transition.
>>> +	 */
>>
>> How about something like
>>
>> /*
>>  * Set forced flag for patches being removed, which is the transition
>>  * patch in KLP_UNPATCHED state or all replaced patches when forcing
>>  * the atomic replace transition.
>>  */
> 
> Or just the first sentence:
> 
> 	/* Set forced flag for patches being removed */
> 
> The rest is visible from the code.
> 
> Either version works for me. If we agree on it then I update
> the text when pushing the patch.

Ok, this works for me too ;-)

Thanks.

> 
> Best Regards,
> Petr