Re: [PATCH] erofs: fix EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS on some UP platforms

[Geert Uytterhoeven]

Hi Gao,

Thanks for your patch!

On Wed, 12 Aug 2026 at 15:12, Gao Xiang <xiang@xxxxxxxxxx> wrote:
> CONFIG_NR_CPUS doesn't define on some UP platforms (e.g. arm), so this
> can cause make oldconfig to loop indefinitely when CONFIG_SMP=n:
>
>  $ make ARCH=arm allmodconfig
>  $ sed -i "/CONFIG_SMP=y/d" .config
>  $ sed -i "/CONFIG_EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS.*/d" .config
>
> EROFS LZMA default maximum decompression streams (EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS) [0] (NEW)
> EROFS LZMA default maximum decompression streams (EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS) [0] (NEW)
> ...

This also fixes EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS silently becoming
zero (and thus breaking decompression completely?) for "automatic"
configs like "make allmodconfig" or "make olddefconfig" on architectures
where NR_CPUS depends on SMP (which is most of them).

>
> Let's guard NR_CPUS with SMP instead of using a hardcoded arbitrary CPU
> uplimit here, similar to commit a3344078101c ("mm: make SPLIT_PTE_PTLOCKS
> depend on SMP").
>
> The initial report from SJ Park was for m68k [1] (m68k is the only arch
> without NR_CPUS in Kconfig), and it will be changed in another patch [2].
>
> [1] https://lore.kernel.org/all/anuyFHLUGDjZWY4K@XiangdeMacBook-Pro.local/T/#u
> [2] https://lore.kernel.org/r/20260731094950.1988084-2-ukleinek@xxxxxxxxxx
>
> Reported-by: SJ Park <sj@xxxxxxxxxx>
> Closes: https://lore.kernel.org/r/20260728065447.91511-1-sj@xxxxxxxxxx
> Reported-by: Guenter Roeck <groeck7@xxxxxxxxx>
> Closes: https://lore.kernel.org/r/87853c96-cc8f-49e6-81b1-02bfe409e372@xxxxxxxxxxxx
> Fixes: c9b47e6b2311 ("erofs: cap LZMA stream pool size")
> Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Signed-off-by: Gao Xiang <xiang@xxxxxxxxxx>

Tested-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>

> --- 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.

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