linux-kernel - Re: [RFC PATCH 1/1] iomap: fix race between iomap_set_range_uptodate and folio_end

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Message-ID: <aUxZTvH46FE9Q6qr@laps>
Date: Wed, 24 Dec 2025 16:21:18 -0500
From: Sasha Levin <sashal@...nel.org>
To: Matthew Wilcox <willy@...radead.org>
Cc: Joanne Koong <joannelkoong@...il.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/1] iomap: fix race between iomap_set_range_uptodate
 and folio_end_read

On Wed, Dec 24, 2025 at 05:27:03PM +0000, Matthew Wilcox wrote:
>On Wed, Dec 24, 2025 at 10:43:58AM -0500, Sasha Levin wrote:
>> On Wed, Dec 24, 2025 at 02:10:19AM +0000, Matthew Wilcox wrote:
>> > So Sasha has produced a very convincingly worded writeup that's
>> > hallucinated.
>>
>> And spent a few hours trying to figure it out so I could unblock testing, but
>> sure - thanks.
>
>When you produce a convincingly worded writeup that's utterly wrong,
>and have a reputation for using AI, that's the kind of reaction you're
>going to get.

A rude and unprofessional one?

>> Here's the full log:
>> https://qa-reports.linaro.org/lkft/sashal-linus-next/build/v6.18-rc7-13806-gb927546677c8/testrun/30618654/suite/log-parser-test/test/exception-warning-fsiomapbuffered-io-at-ifs_free/log
>> , happy to test any patches you might have.
>
>That's actually much more helpful because it removes your incorrect
>assumptions about what's going on.
>
> WARNING: fs/iomap/buffered-io.c:254 at ifs_free+0x130/0x148, CPU#0: msync04/406
>
>That's this one:
>
>        WARN_ON_ONCE(ifs_is_fully_uptodate(folio, ifs) !=
>                        folio_test_uptodate(folio));
>
>which would be fully explained by fuse calling folio_clear_uptodate()
>in fuse_send_write_pages().  I have come to believe that allowing
>filesystems to call folio_clear_uptodate() is just dangerous.  It
>causes assertions to fire all over the place (eg if the page is mapped
>into memory, the MM contains assertions that it must be uptodate).
>
>So I think the first step is simply to delete the folio_clear_uptodate()
>calls in fuse:

[snip]

Here's the log of a run with the change you've provided applied: https://qa-reports.linaro.org/lkft/sashal-linus-next/build/v6.18-rc7-13807-g26a15474eb13/testrun/30620754/suite/log-parser-test/test/exception-warning-fsiomapbuffered-io-at-ifs_free/log

-- 
Thanks,
Sasha