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

[Geert Uytterhoeven]

Hi Günter,

On Fri, 14 Aug 2026 at 20:44, Guenter Roeck <linux@xxxxxxxxxxxx> 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

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds