Re: BISECT result: 6.0.0-RC kernels trigger Firefox snap bug with 6.0.0-rc3 through 6.0.0-rc7

[Phillip Lougher <phillip@squashfs.org.uk>]

On 18/10/2022 13:59, Bagas Sanjaya wrote:
> On Tue, Oct 18, 2022 at 04:24:46PM +0800, Hsin-Yi Wang wrote:
>> Hi Jintao,
>>
>> Thanks for pointing out and sorry for missing this. Does the following
>> diff improve the issue?
>>
>> diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
>> index e56510964b229..7759bd70dfbf2 100644
>> --- a/fs/squashfs/file.c
>> +++ b/fs/squashfs/file.c
>> @@ -600,7 +600,7 @@ static void squashfs_readahead(struct
>> readahead_control *ractl)
>>
>>                          /* Last page (if present) may have trailing
>> bytes not filled */
>>                          bytes = res % PAGE_SIZE;
>> -                       if (pages[nr_pages - 1]->index == file_end && bytes)
>> +                       if ((pages[nr_pages - 1]->index >> shift) ==
>> file_end && bytes)
>>                                  memzero_page(pages[nr_pages - 1], bytes,
>>                                               PAGE_SIZE - bytes);
>>
>>
>> readahead only handles the case that the first page and the last page
>> have the same block index:
>>      index = pages[0]->index >> shift;
>>      if ((pages[nr_pages - 1]->index >> shift) != index)
>>          goto skip_pages;
>>
>> The diff above makes a difference to SQUASHFS_INVALID_BLK case, which
>> will not be handled by squashfs_readahead_fragment() if
>> index==file_end.
>> With the above diff, it will now be memzero_page().
> 
> Hi Hsin-Yi Wang, thanks for the proposed diff. However, it was wrapped,
> so I have to manually type the changes.
> 
> I compiled 6.1-rc1 with your diff applied. For testing, I have both
> hello-world and lxd snaps installed. No problems on running the former.
> On the latter, I got coredump when trying to start lxd services with
> `snap start lxd`. The coredump for lxd processes are attached.
> 
>  From above, I think b09a7a036d2035 ("squashfs: support reading fragments in readahead call") should be reverted until we come up with proper solution.
> 
> Thanks.
> 

I am currently working with the snap developers to identify the issue.

When there is progress, I will post.

Phillip