linux-kernel - Re: [PATCH v2] ext4: check folio uptodate state in ext4_page

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Message-ID: <aTCxrXtrtB0x9C8X@casper.infradead.org>
Date: Wed, 3 Dec 2025 21:54:53 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Theodore Tso <tytso@....edu>
Cc: Deepanshu Kartikey <kartikey406@...il.com>,
	Zhang Yi <yi.zhang@...weicloud.com>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	syzbot+b0a0670332b6b3230a0a@...kaller.appspotmail.com,
	adilger.kernel@...ger.ca, djwong@...nel.org
Subject: Re: [PATCH v2] ext4: check folio uptodate state in
 ext4_page_mkwrite()

On Wed, Dec 03, 2025 at 10:46:57AM -0500, Theodore Tso wrote:
> Matthew, as the page cache maintainer, do we actually need this extra
> rigamarole.  Or can we just skip taking the lock before checking to
> see if the folio is uptodate in ext4_page_mkwrite()?

Oh, this triggered a memory.  Looks like you missed my reply in that
thread.  This patch is bogus.  You need to prevent !uptodate folios from
being referenced by the page tables.

https://groups.google.com/g/syzkaller-bugs/c/kjaCOwdrWVg/m/6Li1dROPBQAJ