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

[Guenter Roeck]

On 8/15/26 04:41, Geert Uytterhoeven wrote:
> 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

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