linux-ext4 - Re: Modification of block device by R/O mount

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Message-ID: <Zrn7LBE8ek1dXIAn@infradead.org>
Date: Mon, 12 Aug 2024 05:08:12 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Dave Chinner <david@...morbit.com>
Cc: Johannes Bauer <canjzymsaxyt@...rnkuller.de>,
	linux-ext4@...r.kernel.org
Subject: Re: Modification of block device by R/O mount

On Fri, Aug 09, 2024 at 11:50:30AM +1000, Dave Chinner wrote:
> You'll need someone who actually knows what metadata ext4 needs to
> modify directly on read-only mounts to tell you exactly what the
> mount is modifying and whether or not it should actually be doing
> that or not. However, I personally wouldn't consider this behaviour
> a bug if it necessary to allow read-only mounts on read-only block
> devices to work reliably...

Modifying page cache without dirtying is in general a bug.  On a
block device we'll mostly get away with it, but it still is asking
for trouble later.  So this probably still warrants fixing, but as
Dave said it isn't exactly a grave bug.