Re: Executable loading issues with erofs on arm?

[Jan Kiszka <jan.kiszka@siemens.com>]

On 08.07.25 19:09, Gao Xiang wrote:
> 
> 
> 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.
> 

Great thanks. I quickly checked backports, and it fits cleanly on 6.12,
but at least 6.1 requires more work to find a home there as well.

> 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.

Yeah, that would explain it. And Stefan (on CC) was on an arm32 as well
back then.

Jan

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