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Date:   Tue, 5 Apr 2022 15:24:51 +0530
From:   Ritesh Harjani <ritesh.list@gmail.com>
To:     anserper@ya.ru
Cc:     linux-ext4@vger.kernel.org,
        Andrew Perepechko <andrew.perepechko@hpe.com>
Subject: Re: [PATCH v3] ext4: truncate during setxattr leads to kernel panic
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References: <20220402084023.1841375-1-anserper@ya.ru>
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On 22/04/02 11:40AM, anserper@ya.ru wrote:
> From: Andrew Perepechko <andrew.perepechko@hpe.com>
>
> When changing a large xattr value to a different large xattr value,
> the old xattr inode is freed. Truncate during the final iput causes
> current transaction restart. Eventually, parent inode bh is marked
> dirty and kernel panic happens when jbd2 figures out that this bh
> belongs to the committed transaction.
>
> A possible fix is to call this final iput in a separate thread.
> This way, setxattr transactions will never be split into two.
> Since the setxattr code adds xattr inodes with nlink=0 into the
> orphan list, old xattr inodes will be properly cleaned up in
> any case.

Ok, I think there is a lot happening in above description. I think part of the
problem I am unable to understand it easily is because I haven't spend much time
with xattr code. But I think below 2 requests will be good to have -

1. Do we have the call stack for this problem handy. I think it will be good to
mention it in the commit message itself. It is sometimes easy to look at the
call stack if someone else encounters a similar problem. That also gives more
idea about where the problem is occuring.

2. Do we have a easy reproducer for this problem? I think it will be a good
   addition to fstests given that this adds another context in calling iput on
   old_ea_inode.

>
> Signed-off-by: Andrew Perepechko <andrew.perepechko@hpe.com>
> HPE-bug-id: LUS-10534

^^^ I think above can be dropped. Any fixes tag instead?

-ritesh