linux-kernel - Re: [PATCH] livepatch: Move error print out of lock protection in klp_enable

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Message-ID: <19e0d24c-366a-a269-8c4d-bf32831e2079@huawei.com>
Date:   Thu, 1 Sep 2022 21:45:30 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Joe Lawrence <joe.lawrence@...hat.com>
CC:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>, <linux-kernel@...r.kernel.org>,
        <live-patching@...r.kernel.org>
Subject: Re: [PATCH] livepatch: Move error print out of lock protection in
 klp_enable_patch()



On 2022/9/1 21:24, Joe Lawrence wrote:
> On 8/31/22 10:27 PM, Zhen Lei wrote:
>> The patch->mod is not a protected object of mutex_lock(&klp_mutex). Since
>> it's in the error handling branch, it might not be helpful to reduce lock
>> conflicts, but it can reduce some code size.
>>
>> Before:
>>    text    data     bss     dec     hex filename
>>   10330     464       8   10802    2a32 kernel/livepatch/core.o
>>
>> After:
>>    text    data     bss     dec     hex filename
>>   10307     464       8   10779    2a1b kernel/livepatch/core.o
>>
> 
> Is a size change expected, or is it just compiler fall out from
> shuffling the code around a little bit?

I thought it was because mutex_lock()/mutex_unlock() was close enough to
reduce a "&klp_mutex" operation. Now, I was wrong.

> 
> I see some arches do a little better, some a little worse with gcc-9.3.0
> cross compilers:

Sorry. This is what I should have done. I built it on x86_64 with gcc-8.4.0

> 
> Before
> ------
>    text    data     bss     dec     hex filename
>    8490     600       8    9098    238a arm64/kernel/livepatch/core.o
>    9424     680       8   10112    2780 s390/kernel/livepatch/core.o
>    9802     228       4   10034    2732 ppc32/kernel/livepatch/core.o
>   13746     456       8   14210    3782 ppc64le/kernel/livepatch/core.o
>   10443     464       8   10915    2aa3 x86_64/kernel/livepatch/core.o
> 
> 
> After
> -----
>    text    data     bss     dec     hex filename
>    8514     600       8    9122    23a2 arm64/kernel/livepatch/core.o
>    9424     680       8   10112    2780 s390/kernel/livepatch/core.o
>    9818     228       4   10050    2742 ppc32/kernel/livepatch/core.o
>   13762     456       8   14226    3792 ppc64le/kernel/livepatch/core.o
>   10446     464       8   10918    2aa6 x86_64/kernel/livepatch/core.o
> 
> In which case, I'd just omit the size savings from the commit msg.

OK. Should I send v2 to update commit message?

> 
>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
>> ---
>>  kernel/livepatch/core.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
>> index 42f7e716d56bf72..cb7abc821a50584 100644
>> --- a/kernel/livepatch/core.c
>> +++ b/kernel/livepatch/core.c
>> @@ -1041,9 +1041,9 @@ int klp_enable_patch(struct klp_patch *patch)
>>  	mutex_lock(&klp_mutex);
>>  
>>  	if (!klp_is_patch_compatible(patch)) {
>> +		mutex_unlock(&klp_mutex);
>>  		pr_err("Livepatch patch (%s) is not compatible with the already installed livepatches.\n",
>>  			patch->mod->name);
>> -		mutex_unlock(&klp_mutex);
>>  		return -EINVAL;
>>  	}
>>  
>>
> 
> That said, I don't see anything obviously wrong about the change (we
> don't need to sync our error msgs, right?) so:

Yes

> 
> Acked-by: Joe Lawrence <joe.lawrence@...hat.com>

Thanks

> 

-- 
Regards,
  Zhen Lei