linux-kernel - Re: [PATCH v3] mm, slub: change run-time assertion in kmalloc

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Message-ID: <a1287a21-bcbb-77ed-c88d-f5890b785213@kernel.org>
Date:   Mon, 17 May 2021 17:43:22 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>, akpm@...ux-foundation.org,
        iamjoonsoo.kim@....com, rientjes@...gle.com, penberg@...nel.org,
        cl@...ux.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        naresh.kamboju@...aro.org, clang-built-linux@...glegroups.com,
        linux-next@...r.kernel.org, ndesaulniers@...gle.com,
        lkft-triage@...ts.linaro.org, sfr@...b.auug.org.au, arnd@...db.de,
        Marco Elver <elver@...gle.com>
Subject: Re: [PATCH v3] mm, slub: change run-time assertion in kmalloc_index()
 to compile-time

On 5/17/2021 5:38 PM, Hyeonggon Yoo wrote:
> On Sat, May 15, 2021 at 11:34:49PM -0700, Nathan Chancellor wrote:
>> This should work I think:
> 
> compiled well with clang-10.0.1, clang-11.0.0,
> and gcc-10.2.0 with x86_64 default config.
> 
> is the condition CONFIG_CLANG_VERSION > 110000,
> not including 110000 it self?

Ah sorry, that should definitely be >= :(

That is what I get for writing an email that late... in reality, it 
probably won't matter due to the availability of 11.0.1 and 11.1.0 but 
it should absolutely be changed.

I have not given Nick's patch a go yet but would something like this be 
acceptable? If so, did you want me to send a formal fixup patch or did 
you want to send a v4? I have no personal preference.

>> diff --git a/include/linux/slab.h b/include/linux/slab.h
>> index 9d316aac0aba..1b653266f2aa 100644
>> --- a/include/linux/slab.h
>> +++ b/include/linux/slab.h
>> @@ -413,7 +413,7 @@ static __always_inline unsigned int __kmalloc_index(size_t size,
>>   	if (size <=  16 * 1024 * 1024) return 24;
>>   	if (size <=  32 * 1024 * 1024) return 25;
>>   
>> -	if (size_is_constant)
>> +	if ((IS_ENABLED(CONFIG_CC_IS_GCC) || CONFIG_CLANG_VERSION > 110000) && size_is_constant)
>>   		BUILD_BUG_ON_MSG(1, "unexpected size in kmalloc_index()");
>>   	else
>>   		BUG();