linux-ext4 - Re: [PATCH] tune2fs: prohibit toggling uninit

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Message-ID: <20191121182240.GJ4262@mit.edu>
Date:   Thu, 21 Nov 2019 13:22:40 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     linux-ext4 <linux-ext4@...r.kernel.org>,
        eric.saint.etienne@...cle.com
Subject: Re: [PATCH] tune2fs: prohibit toggling uninit_bg on live filesystems

On Wed, Nov 20, 2019 at 11:32:55AM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@...cle.com>
> 
> An internal customer followed an erroneous AskUbuntu article[1] to try to
> change the UUID of a live ext4 filesystem.  The article claims that you
> can work around tune2fs' "cannot change UUID on live fs" error by
> disabling uninit_bg, changing the UUID, and re-enabling the feature.
> 
> This led to metadata corruption because tune2fs' journal descriptor
> rewrite races with regular filesystem writes.  Therefore, prevent
> administrators from turning on or off uninit_bg on a mounted fs.
> 
> [1] https://askubuntu.com/questions/132079/how-do-i-change-uuid-of-a-disk-to-whatever-i-want/195839#459097
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>

Thanks, applied.

					- Ted