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

On 8/11/26 12:27, Geert Uytterhoeven wrote:
> On Mon, 3 Aug 2026 at 11:12, Uwe Kleine-König
> <[email protected]> wrote:
>> On Mon, Aug 03, 2026 at 10:09:06AM +0200, Geert Uytterhoeven wrote:
>>> On Tue, 28 Jul 2026 at 08:55, SJ Park <[email protected]> wrote:
>>>> I don't have a m68k testfarm, either.  I'm doing crossbuild [1].  Hopefully you
>>>> could also reproduce it.
>>
>> FTR, I don't have m68k hardware either, but as this is a build time
>> failure installing the Debian package gcc-m68k-linux-gnu and then doing
>> builds using
>>
>>          make ARCH=m68k CROSS_COMPILE=m68k-linux-gnu-
>>
>> is good enough to reproduce the failure.
>>
>>> I think you can reproduce some of the issues on most architectures
>>> with a non-SMP kernel, cfr. my reply[1] to Uwe's proposed fix.
>>> Unfortunately the Kconfig warning only shows up on architectures that
>>> don't define NR_CPUS (because they do not support SMP) at all,
>>> while ending up with zero streams is probably a runtime failure.
>>>
>>> [1] https://lore.kernel.org/CAMuHMdVGKX=3cfOrLWp1uSHX76xf1-=C0+GVCXkA8JTqNPg-ew@mail.gmail.com
>>
>> I guess EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS should depend on SMP and
>> it's use should be conditionalized using something like
>>
>> diff --git a/fs/erofs/decompressor_lzma.c b/fs/erofs/decompressor_lzma.c
>> index 6b0cdb446c6a..c00e94f8206f 100644
>> --- a/fs/erofs/decompressor_lzma.c
>> +++ b/fs/erofs/decompressor_lzma.c
>> @@ -50,9 +50,13 @@ static int __init z_erofs_lzma_init(void)
>>          unsigned int i;
>>
>>          /* by default, use # of possible CPUs instead */
>> -       if (!z_erofs_lzma_nstrms)
>> -               z_erofs_lzma_nstrms = min_t(unsigned int, num_possible_cpus(),
>> -                               CONFIG_EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS);
>> +       if (!z_erofs_lzma_nstrms) {
>> +               if (IS_ENABLED(CONFIG_SMP))
>> +                       z_erofs_lzma_nstrms = min_t(unsigned int, num_possible_cpus(),
>> +                                       CONFIG_EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS);
>> +               else
>> +                       z_erofs_lzma_nstrms = 1;
>> +       }
>>
>>          for (i = 0; i < z_erofs_lzma_nstrms; ++i) {
>>                  struct z_erofs_lzma *strm = kzalloc_obj(*strm);
> 
> LGTM.
> 
>>
>> I played a bit with the definition of
>> EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS in fs/erofs/Kconfig, but didn't
>> find a way to define it that both uses NR_CPUS and doesn't generate a
>> warning with ARCH=m68k.
> 
> Any progress with fixing this for v7.2?
> 
> NR_CPUS depends on SMP on most architectures, so you get e.g.
> with ARCH=arm allmodconfig + CONFIG_SMP=n:
> 
>      CONFIG_EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS=0
> 
> X86 defines NR_CPUS unconditionally, so there it works as expected.
> Thanks!
> 
FWIW, m68k:allmodconfig now fails to build due to this problem all the
way back to v6.6.y.

Guenter