linux-kernel - Re: Known and unfixed active data loss bug in MM + XFS with large folios since Dec 2021 (any kernel from 6.1 upwards)

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Message-ID: <ZuNjNNmrDPVsVK03@casper.infradead.org>
Date: Thu, 12 Sep 2024 22:55:00 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Christian Theune <ct@...ingcircus.io>
Cc: linux-mm@...ck.org,
	"linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, axboe@...nel.dk,
	Daniel Dao <dqminh@...udflare.com>,
	Dave Chinner <david@...morbit.com>, clm@...a.com,
	regressions@...ts.linux.dev, regressions@...mhuis.info
Subject: Re: Known and unfixed active data loss bug in MM + XFS with large
 folios since Dec 2021 (any kernel from 6.1 upwards)

On Thu, Sep 12, 2024 at 11:18:34PM +0200, Christian Theune wrote:
> This bug is very hard to reproduce but has been known to exist as a
> “fluke” for a while already. I have invested a number of days trying
> to come up with workloads to trigger it quicker than that stochastic
> “once every few weeks in a fleet of 1.5k machines", but it eludes
> me so far. I know that this also affects Facebook/Meta as well as
> Cloudflare who are both running newer kernels (at least 6.1, 6.6,
> and 6.9) with the above mentioned patch reverted. I’m from a much
> smaller company and seeing that those guys are running with this patch
> reverted (that now makes their kernel basically an untested/unsupported
> deviation from the mainline) smells like desparation. I’m with a
> much smaller team and company and I’m wondering why this isn’t
> tackled more urgently from more hands to make it shallow (hopefully).

This passive-aggressive nonsense is deeply aggravating.  I've known
about this bug for much longer, but like you I am utterly unable to
reproduce it.  I've spent months looking for the bug, and I cannot.