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Message-ID: <d1f6c2da-4473-d0ae-88a2-dc379a9857e8@gmail.com>
Date:   Tue, 18 Oct 2022 15:33:25 +0700
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Subject: Re: BISECT result: 6.0.0-RC kernels trigger Firefox snap bug with
 6.0.0-rc3 through 6.0.0-rc7
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From:   Bagas Sanjaya <bagasdotme@gmail.com>
To:     Jintao Yin <nicememory@gmail.com>, phillip@squashfs.org.uk
Cc:     linux-kernel@vger.kernel.org, marcmiltenberger@gmail.com,
        mirsad.todorovac@alu.unizg.hr, regressions@leemhuis.info,
        regressions@lists.linux.dev, srw@sladewatkins.net
References: <20221015205936.5735-1-phillip@squashfs.org.uk>
 <20221018021507.612-1-nicememory@gmail.com>
 <2522e5d5-5f8a-c5e9-4864-a82f0e6d2512@gmail.com>
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On 10/18/22 14:23, Bagas Sanjaya wrote:
> On 10/18/22 09:15, Jintao Yin wrote:
>> Hi Phillip,
>>   There is a logical bug in commit 8fc78b6fe24c36b151ac98d7546591ed92083d4f
>>   which is parent commit of commit b09a7a036d2035b14636cd4c4c69518d73770f65.
>>   
>>   In function squashfs_readahead(...),
>>   file_end is initialized with i_size_read(inode) >> msblk->block_log,
>>   which means the last block index of the file.
>>   But later in the logic to check if the page is last one or not the
>>   code is 
>>     if (pages[nr_pages - 1]->index == file_end && bytes) {
>>       ...
>>     }
>>   , use file_end as the last page index of file but actually is the last
>>   block index, so for the common setup of page and block size, the first 
>>   comparison is true only when pages[nr_pages - 1]->index is 0.
>>   Otherwise, the trailing bytes of last page won't be zeroed.
>>
>>   Maybe it's the real cause of the snap bug in some way.
>>
> 
> Hi Jintao, thanks for explaining the real culprit. However, I'd like to
> see the fixup patch from you so that we can test.
> 

Sorry for inconvenience. Hsin-Yi Wang have already submitted the candidate
fix at [1]. Thanks anyway.

[1]: https://lore.kernel.org/lkml/CAJMQK-hgQEkhgpO9VFOCgn-cKtVsr7Hb_58pAYiGoDi5SzGZtA@mail.gmail.com/

-- 
An old man doll... just what I always wanted! - Clara