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: <CAHk-=wjsrwuU9uALfif4WhSg=kpwXqP2h1ZB+zmH_ORDsrLCnQ@mail.gmail.com>
Date: Thu, 19 Sep 2024 05:03:23 +0200
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Dave Chinner <david@...morbit.com>
Cc: Matthew Wilcox <willy@...radead.org>, Chris Mason <clm@...a.com>, Jens Axboe <axboe@...nel.dk>, 
	Christian Theune <ct@...ingcircus.io>, linux-mm@...ck.org, 
	"linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Daniel Dao <dqminh@...udflare.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, 19 Sept 2024 at 03:43, Dave Chinner <david@...morbit.com> wrote:
>
> Should we be asking for 6758c1128ceb to be backported to all
> stable kernels then?

I think we should just do the simple one-liner of adding a
"xas_reset()" to after doing xas_split_alloc() (or do it inside the
xas_split_alloc()).

That said, I do also think it would be really good if the 'xa_lock*()'
family of functions also had something like a

        WARN_ON_ONCE(xas->xa_node && !xa_err(xas->xa_node));

which I think would have caught this. Because right now nothing at all
checks "we dropped the xa lock, and held xas state over it".

               Linus