linux-ext4 - Re: Issue with ext4 filesystem corruption when writing to a file after disk exhaustion

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Message-ID: <20250715034204.GD23343@mit.edu>
Date: Mon, 14 Jul 2025 23:42:04 -0400
From: "Theodore Ts'o" <tytso@....edu>
To: Jiany Wu <wujianyue000@...il.com>
Cc: "Darrick J. Wong" <djwong@...nel.org>, yi.zhang@...wei.com, jack@...e.cz,
        linux-ext4@...r.kernel.org
Subject: Re: Issue with ext4 filesystem corruption when writing to a file
 after disk exhaustion

On Tue, Jul 15, 2025 at 09:27:01AM +0800, Jiany Wu wrote:
> 
> Thanks indeed for the clarification, it is clear now.
> OK, if using a loopback mounted image on a disk, underlying file
> system full then the block device will have I/O error.
> This loopback mount belongs to a third party common config. I'll
> fallocate lower disk space to not exhaust disk as a work around
> firstly.

The question I'd ask is *why* someone set up that loopback mount in
the first place.  As a guess, perhaps the goal was to restrict the
mount of disk space could be used for log files in /var/log, so that
if there is runaway logging, that all of the free space on the root
partition won't be consumed.

But if that's the case, there are much better ways of achieving the
same goal.  For example, in addition to using log rotation programs,
you could back that up with using project quotas , which restricts how
much space can get used in a subdirectory.

Cheers,

					- Ted