linux-ext4 - [QUESTION] question for commit 2d01ddc86606 ("ext4: save error info to sb through journal if available")

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Message-ID: <05ff3a17-6559-9317-a382-f0a02fa59926@huawei.com>
Date:   Wed, 25 Aug 2021 10:13:03 +0800
From:   yangerkun <yangerkun@...wei.com>
To:     Jan Kara <jack@...e.cz>
CC:     "Theodore Y . Ts'o" <tytso@....edu>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        <yangerkun@...wei.com>
Subject: [QUESTION] question for commit 2d01ddc86606 ("ext4: save error info
 to sb through journal if available")

Hi Jan,

There is a question about 2d01ddc86606 ("ext4: save error info to sb 
through journal if available"). This commit describe that we can have 
checksum failure with follow case:

1. ext4_handle_error will call ext4_commit_super which write directly to 
the superblock
2. At the same time, jounalled update of the superblock is ongoing

However, after commit 05c2c00f3769 ("ext4: protect superblock 
modifications with a buffer lock"), all the update for superblock and 
the csum will be protected with buffer lock. It seems we won't get a 
csum error after that commit and the journal logic in 
flush_stashed_error_work seems useless.

Maybe there is something missing... Can you help to explain more for that...

Thanks,
Kun.