Re: [PATCH v3] erofs: cap LZMA stream pool size

On 8/15/26 04:41, Geert Uytterhoeven wrote:
> Hi Günter,
> 
> On Fri, 14 Aug 2026 at 20:44, Guenter Roeck <[email protected]> wrote:
>> On 8/14/26 11:26, Gao Xiang wrote:
>>> On Wed, Aug 12, 2026 at 07:25:50AM -0700, Guenter Roeck wrote:
>>>>>> Thank you, that seems to work (despite still seeing the warning on m68k,
>>>>>> as NR_CPUS does not exist).
>>>>>>
>>>>>>          $ make ARCH=m68k allmodconfig
>>>>>>         fs/erofs/Kconfig:137:warning: range is invalid
>>>>>>
>>>>>>     Warning...
>>>>>
>>>>> Yes, other arches shouldn't have the warning because I think other
>>>>> arches (including microblaze) defines NR_CPUS in Kconfig, except m68k.
>>>>
>>>> That is not entirely true. openrisc only has it if SMP=y. But it still
>>>> does not generate the warning for some reason.
>>>
>>> I looked into the documentation a bit
>>> (https://docs.kernel.org/kbuild/kconfig-language.html), especially the
>>> following parts:
>>>
>>>    - type definition: “bool”/”tristate”/”string”/”hex”/”int” ...
>>>    - input prompt: “prompt” <prompt> [“if” <expr>] ...
>>>        and "If a prompt is not present, the config option is
>>>             a non-visible symbol, ..."
>>>
>>>    - dependencies: “depends on” <expr> [“if” <expr>] ...
>>>    - Menu dependencies ..
>>>
>>> and I think that is true, taking openrisc for example:
>>>
>>> config NR_CPUS
>>>           int "Maximum number of CPUs (2-32)"
>>>           range 2 32
>>>           depends on SMP
>>>           default "2"
>>>
>>> which can be transformed into
>>>
>>> config NR_CPUS
>>>           int
>>>        prompt "Maximum number of CPUs (2-32)"
>>>        range 2 32
>>>        depends on SMP
>>>           default "2"
>>>
>>> which can be then transformed into
>>>
>>> config NR_CPUS
>>>           int
>>>        prompt "Maximum number of CPUs (2-32)" if SMP
>>>        range 2 32 if SMP
>>>           default "2" if SMP
>>>
>>> so if `SMP=n`, it's equivalent to
>>>
>>> config NR_CPUS
>>>           int
>>>
>>> so NR_CPUS symbol is still there I think (and its value is 0.)
>>>
>> $ grep NR_CPUS .config
>> CONFIG_FORCE_NR_CPUS=y
>> $ grep EROFS .config
>> CONFIG_EROFS_FS=y
>> # CONFIG_EROFS_FS_DEBUG is not set
>> CONFIG_EROFS_FS_XATTR=y
>> CONFIG_EROFS_FS_POSIX_ACL=y
>> CONFIG_EROFS_FS_SECURITY=y
>> CONFIG_EROFS_FS_BACKED_BY_FILE=y
>> CONFIG_EROFS_FS_ZIP=y
>> CONFIG_EROFS_FS_ZIP_LZMA=y
>> CONFIG_EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS=0
>> # CONFIG_EROFS_FS_ZIP_DEFLATE is not set
>> # CONFIG_EROFS_FS_ZIP_ZSTD is not set
>> # CONFIG_EROFS_FS_ZIP_ACCEL is not set
>> # CONFIG_EROFS_FS_PCPU_KTHREAD is not set
>> # CONFIG_EROFS_FS_PAGE_CACHE_SHARE is not set
>>
>> The symbol may be there internally, but it does not show up in .config.
> 
>      config EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS
>      ...
>      range 1 NR_CPUS
> 
> Apparently the default value picked by "automatic" configs like
> allmodconfig and defconfig is the last item from the range.
> If NR_CPUS exists internally (e.g. openrisc and arm), you end up with
> the "undefined value", aka zero:
> 
>      CONFIG_EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS=0
> 
> As NR_CPUS did not exist on m68k at all, you ended up with the NR_CPUS
> literal:
> 
>      CONFIG_EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS=NR_CPUS
> 

Upstream commit a64d500b0078 ("erofs: fix EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS
on some UP platforms") should fix that problem. Apparently it did not only
affect openrisc.

Thanks,
Guenter