Re: Executable loading issues with erofs on arm?

[Gao Xiang <hsiangkao@linux.alibaba.com>]

On 2025/7/9 01:01, Jan Kiszka wrote:
> On 08.07.25 18:39, Jan Kiszka wrote:
>> On 08.07.25 17:57, Gao Xiang wrote:
>>>
>>>
>>> On 2025/7/8 23:36, Gao Xiang wrote:
>>>>
>>>>
>>>> On 2025/7/8 23:32, Gao Xiang wrote:
>>>>>
>>>>>
>>>>> On 2025/7/8 23:22, Jan Kiszka wrote:
>>>>>> On 08.07.25 17:12, Gao Xiang wrote:
>>>>>>> Hi Jan,
>>>>>>>
>>>>>>> On 2025/7/8 20:43, Jan Kiszka wrote:
>>>>>>>> On 08.07.25 14:41, Jan Kiszka wrote:
>>>>>>>>> Hi all,
>>>>>>>>>
>>>>>>>>> for some days, I'm trying to understand if we have an integration
>>>>>>>>> issue
>>>>>>>>> with erofs or rather some upstream bug. After playing with various
>>>>>>>>> parameters, it rather looks like the latter:
>>>>>>>>>
>>>>>>>>> $ ls -l erofs-dir/
>>>>>>>>> total 132
>>>>>>>>> -rwxr-xr-x 1 1000 users 132868 Jul  8 10:50 dash
>>>>>>>>> (from Debian bookworm)
>>>>>>>>> $ mkfs.erofs -z lz4hc erofs.img erofs-dir/
>>>>>>>>> mkfs.erofs 1.8.6 (trixie version, but same happens with bookworm
>>>>>>>>> 1.5)
>>>>>>>>> Build completed.
>>>>>>>>> ------
>>>>>>>>> Filesystem UUID: aae0b2f0-4ee4-4850-af49-3c1aad7fa30c
>>>>>>>>> Filesystem total blocks: 17 (of 4096-byte blocks)
>>>>>>>>> Filesystem total inodes: 2
>>>>>>>>> Filesystem total metadata blocks: 1
>>>>>>>>> Filesystem total deduplicated bytes (of source files): 0
>>>>>>>>>
>>>>>>>>> Now I have 6.15-rc5 and a defconfig-close setting for the 32-bit ARM
>>>>>>>>> target BeagleBone Black. When booting into init=/bin/sh, then
>>>>>>>>> running
>>>>>>>>>
>>>>>>>>> # mount -t erofs /dev/mmcblk0p1 /mnt
>>>>>>>>> erofs (device mmcblk0p1): mounted with root inode @ nid 36.
>>>>>>>>> # /mnt/dash
>>>>>>>>> Segmentation fault
>>>>
>>>> Two extra quick questions:
>>>>    - If the segfault happens, then if you run /mnt/dash again, does
>>>>      segfault still happen?
>>>>
>>>>    - If the /mnt/dash segfault happens, then if you run
>>>>        cat /mnt/dash > /dev/null
>>>>        /mnt/dash
>>>>      does segfault still happen?
>>>
>>> Oh, sorry I didn't read the full hints, could you check if
>>> the following patch resolve the issue (space-damaged)?
>>>
>>> diff --git a/fs/erofs/data.c b/fs/erofs/data.c
>>> index 6a329c329f43..701490b3ef7d 100644
>>> --- a/fs/erofs/data.c
>>> +++ b/fs/erofs/data.c
>>> @@ -245,6 +245,7 @@ void erofs_onlinefolio_end(struct folio *folio, int
>>> err)
>>>          if (v & ~EROFS_ONLINEFOLIO_EIO)
>>>                  return;
>>>          folio->private = 0;
>>> +       flush_dcache_folio(folio);
>>>          folio_end_read(folio, !(v & EROFS_ONLINEFOLIO_EIO));
>>>   }
>>>
>>
>> Yeah, indeed that seem to have helped with the minimal test. Will do the
>> full scenario test (complete rootfs) next.
>>
> 
> And that looks good as! Thanks a lot for that quick fix - hoping that is
> the real solution already.
> 
> BTW, that change does not look very specific to the armhf arch, rather
> like we were lucky that it didn't hit elsewhere, right?

I may submit a formal patch tomorrow.

This issue doesn't impact x86 and arm64. For example on arm64,
PG_dcache_clean is clear when it's a new page cache folio.

But it seems on arm platform flush_dcache_folio() does more
to handle D-cache aliasing so some caching setup may be
impacted.

Thanks,
Gao Xiang

> 
> Jan
>