linux-kernel - 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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Message-ID: <2522e5d5-5f8a-c5e9-4864-a82f0e6d2512@gmail.com>
Date:   Tue, 18 Oct 2022 14:23:42 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     Jintao Yin <nicememory@...il.com>, phillip@...ashfs.org.uk
Cc:     linux-kernel@...r.kernel.org, marcmiltenberger@...il.com,
        mirsad.todorovac@....unizg.hr, regressions@...mhuis.info,
        regressions@...ts.linux.dev, srw@...dewatkins.net
Subject: Re: BISECT result: 6.0.0-RC kernels trigger Firefox snap bug with
 6.0.0-rc3 through 6.0.0-rc7

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.

Thanks.

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