Message-ID: <2bbc2df8-5fcf-b216-7aa0-192e27bac6e7@xen0n.name>
Date:   Fri, 15 Sep 2023 22:19:15 +0800
From:   WANG Xuerui <kernel@...0n.name>
To:     Guenter Roeck <linux@...ck-us.net>, Helge Deller <deller@....de>,
        Huacai Chen <chenhuacai@...nel.org>
Cc:     loongarch@...ts.linux.dev,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] LoongArch: Fix lockdep static memory detection

Hi,

On 9/15/23 22:07, Guenter Roeck wrote:
> Hi Helge,
>
> On 9/15/23 03:10, Helge Deller wrote:
>> On 9/15/23 11:23, Huacai Chen wrote:
>>> On Fri, Sep 15, 2023 at 4:16 PM Helge Deller <deller@....de> wrote:
>>>>
>>>> On 9/15/23 05:22, Huacai Chen wrote:
>>>>> Hi Helge,
>>>>>
>>>>> On Wed, Sep 13, 2023 at 3:18 AM Helge Deller <deller@....de> wrote:
>>>>>>
>>>>>> Since commit 0a6b58c5cd0d ("lockdep: fix static memory detection 
>>>>>> even
>>>>>> more") the lockdep code uses is_kernel_core_data(), 
>>>>>> is_kernel_rodata()
>>>>>> and init_section_contains() to verify if a lock is located inside a
>>>>>> kernel static data section.
>>>>>>
>>>>>> This change triggers a failure on LoongArch, for which the 
>>>>>> vmlinux.lds.S
>>>>>> script misses to put the locks (as part of in the .data.rel symbols)
>>>>>> into the Linux data section.
>>>>>> This patch fixes the lockdep problem by moving *(.data.rel*) symbols
>>>>>> into the kernel data section (from _sdata to _edata).
>>>>>>
>>>>>> Additionally, move other wrongly assigned symbols too:
>>>>>> - altinstructions into the _initdata section,
>>>>
>>>>> I think altinstructions cannot  be put into _initdata because it will
>>>>> be used by modules.
>>>>
>>>> No.
>>>> arch/loongarch/kernel/vmlinux.lds.S is used for the static parts of 
>>>> the kernel
>>>> and altinstructions are replaced before modules are loaded.
>>>> For altinstructions in modules the linker script 
>>>> scripts/module.lds.S is used.
>>
>>> OK, then what about .got/.plt? It seems arm64 also doesn't put them in
>>> the data section.
>>
>> arm64 seems to throw away all plt entries already at link time (and 
>> just keeps
>> the got.plt in the read-only data section).
>> It even checks at link time, that there are no plt entries in the 
>> binary:
>>          ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure 
>> linkages detected!")
>>
>> I don't know for loongarch, but if you need the plt entries for 
>> loongarch, it's
>> safest & best to put them into the read-only data section too, which 
>> is what my patch does.
>> Up to now, you have them completely outside of code & data sections.
>>
>> In the end you need to decide for your platform. My patch is a 
>> suggestion, which I think
>> is correct (untested by me, but Guenter replied he tested it).
>> But to fix the lockdep problem at minimum the move of the .data.rel 
>> section
>> is needed.
>>
>
> Just my $0.02 .. it might make sense to concentrate on the minimum to 
> get the immediate
> problem fixed. Loongarch maintainers can then decide at their own pace 
> if they want
> to apply any of the other changes you suggested. After all, unless I 
> am missing
> something, those additional changes are not really needed in stable 
> releases.

Sorry for coming late, but as reviewer of arch/loongarch, I'd agree with 
Guenter and Helge here: let's fix the immediate problem and investigate 
the rest later -- it's not like the problems are *definitely* orthogonal 
in this case, and at least *some* progress would be appreciated.

I'll try to reproduce the problem and test the fix during the weekend, 
so hopefully Huacai can get the fix in before -rc2 or -rc3. Thanks for 
the attention and fix.

-- 
WANG "xen0n" Xuerui

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