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

[Guenter Roeck]

On 8/12/26 03:54, Gao Xiang wrote:
> Hi Geert,
>
> On Wed, Aug 12, 2026 at 11:30:14AM +0200, Geert Uytterhoeven wrote:
> > Hi Gao,
> >
> > On Wed, 12 Aug 2026 at 01:37, Gao Xiang <xiang@xxxxxxxxxx> wrote:
> > > On Tue, Aug 11, 2026 at 03:37:38PM -0400, Michael Bommarito wrote:
> > > > On Tue, Aug 11, 2026 at 3:35 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > > > > > Any progress with fixing this for v7.2?
> > > >
> > > > I would like to fix this since I started the problem with the original
> > > > patch, but I feel a bit stuck.  My v1 and v2 patches would not have
> > > > triggered the build failure, but Gao made valid points about the
> > > > trade-offs that led us to this v3.  Maybe it would be worth your
> > > > opinion on the config approach in those earlier patches?
> > >
> > > Sorry about the late reply.
> > >
> > > As I said, I really dislike hardcoded range, but it is an issue that no
> > > NR_CPUS definition on CONFIG_SMP:
> > >
> > > I wonder if the following diff resolves the m68k issue (I'm not an
> > > Kconfig expert but it seems to work on x86_64 !CONFIG_SMP):
> > >
> > > diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
> > > index 8ca1767dafb6..2dfc313588d2 100644
> > > --- a/fs/erofs/Kconfig
> > > +++ b/fs/erofs/Kconfig
> > > @@ -134,7 +134,8 @@ config EROFS_FS_ZIP_LZMA
> > >   config EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS
> > >          int "EROFS LZMA default maximum decompression streams"
> > >          depends on EROFS_FS_ZIP_LZMA
> > > -       range 1 NR_CPUS
> > > +       range 1 NR_CPUS if SMP
> > > +       range 1 1 if !SMP
> > >          default 16
> > >          help
> > >            By default EROFS allocates one LZMA decompression stream per CPU.
> >
> > 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.

> The following diff can eliminate the m68k warning above, I think m68k
> folks could consider this way if you really don't want to define an
> explicit NR_CPUS.  Anyway, I think it should go with another patch:
>
> ```
> diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
> index 11835eb59d94..90499f126c73 100644
> --- a/arch/m68k/Kconfig
> +++ b/arch/m68k/Kconfig
> @@ -44,6 +44,9 @@ config M68K
>   	select UACCESS_MEMCPY if !MMU
>   	select ZONE_DMA
>   
> +config NR_CPUS
> +	int

I would suggest to add

	default 1

Guenter

> +
>   config CPU_BIG_ENDIAN
>   	def_bool y
> ```
>
> I will try to form a formal patch (with the diff in the previous reply)
> directly to Linus (since I don't have other urgent patches for
> Linux 7.2.)
>
> Thanks,
> Gao Xiang