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Date:   Fri, 4 Aug 2023 11:57:22 -0500
From:   Frederick Lawler <fred@cloudflare.com>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Daniel Dao <dqminh@cloudflare.com>, linux-fsdevel@vger.kernel.org,
        Dave Chinner <david@fromorbit.com>,
        kernel-team <kernel-team@cloudflare.com>,
        linux-kernel <linux-kernel@vger.kernel.org>, djwong@kernel.org
Subject: Re: Kernel NULL pointer deref and data corruptions with xfs on 6.1
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Hi Matthew,

On Thu, Jul 27, 2023 at 01:27:56PM +0100, Matthew Wilcox wrote:
> On Thu, Jul 27, 2023 at 11:25:33AM +0100, Daniel Dao wrote:
> > On Thu, Jul 27, 2023 at 4:27 AM Matthew Wilcox <willy@infradead.org> wrote:
> > >
> > > On Fri, Jul 21, 2023 at 11:49:04AM +0100, Daniel Dao wrote:
> > > > We do not have a reproducer yet, but we now have more debugging data
> > > > which hopefully
> > > > should help narrow this down. Details as followed:
> > > >
> > > > 1. Kernel NULL pointer deferencences in __filemap_get_folio
> > > >
> > > > This happened on a few different hosts, with a few different repeated addresses.
> > > > The addresses are 0000000000000036, 0000000000000076,
> > > > 00000000000000f6. This looks
> > > > like the xarray is corrupted and we were trying to do some work on a
> > > > sibling entry.
> > >
> > > I think I have a fix for this one.  Please try the attached.
> > 
> > For some reason I do not see the attached patch. Can you resend it, or
> > is it the same
> > one as in https://bugzilla.kernel.org/show_bug.cgi?id=216646#c31 ?
> 
> Yes, that's the one, sorry.

I setup a kernel with this patch to deploy out. It'll take some time to
see any results from that. I did run your multiorder.c changes with/without
the change to lib/xarray.c and that seemed to work as intended. I didn't see
any regressions across multiple seeds with our kernel config.

Fred