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

[Gao Xiang <xiang@kernel.org>]

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@kernel.org> 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@roeck-us.net> 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.

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
+
 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