linux-kernel - Re: Regression: NULL pointer dereference after NFS_V4_2_READ

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Date:   Thu, 15 Jun 2023 15:38:48 -0400
From:   Anna Schumaker <schumaker.anna@...il.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <Anna.Schumaker@...app.com>,
        linux-nfs <linux-nfs@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>
Subject: Re: Regression: NULL pointer dereference after NFS_V4_2_READ_PLUS
 (commit 7fd461c47)

On Thu, Jun 15, 2023 at 1:16 PM Anna Schumaker <schumaker.anna@...il.com> wrote:
>
> On Thu, Jun 15, 2023 at 1:04 PM Anna Schumaker <schumaker.anna@...il.com> wrote:
> >
> > On Thu, Jun 15, 2023 at 9:01 AM Anna Schumaker <schumaker.anna@...il.com> wrote:
> > >
> > > On Thu, Jun 15, 2023 at 4:55 AM Krzysztof Kozlowski
> > > <krzysztof.kozlowski@...aro.org> wrote:
> > > >
> > > > On 15/06/2023 10:52, Krzysztof Kozlowski wrote:
> > > > > On 14/06/2023 22:55, Anna Schumaker wrote:
> > > > >>>>> Still null ptr (built on 420b2d4 with your patch):
> > > > >>>>
> > > > >>>> We're through the merge window and at rc1 now, so I can spend more
> > > > >>>> time scratching my head over your bug again. We've come up with a
> > > > >>>> patch (attached) that adds a bunch of printks to show us what the
> > > > >>>> kernel thinks is going on. Do you mind trying it out and letting us
> > > > >>>> know what gets printed out? You'll need to make sure
> > > > >>>> CONFIG_NFS_V4_2_READ_PLUS is enabled when compiling the kernel.
> > > > >>>
> > > > >>> The patch does not apply. I tried: v6.4-rc1, v6.4-rc5, next-20230609.
> > > > >>
> > > > >> Can you try the attached patch on top of my 3-patch series from the
> > > > >> other day, and let me know what gets printed out? It adds a bunch of
> > > > >> printk()s at strategic points to print out what is going on with the
> > > > >> xdr scratch buffer since it's suddenly a bad memory address after
> > > > >> working for a bit on your machine.
> > > > >>
> > > > >
> > > > > Here you have entire log - attached (113 kB, I hope goes past mailing
> > > > > lists/spam filters).
> > > >
> > > > As expected this bounced from the mailing lists, but I hope you got it.
> > > > If not, let me know.
> > >
> > > I did still receive it. Thanks!
> >
> > Can you swap out yesterday's patch with this patch? I've adjusted what
> > gets printed out, and added printk()s to xdr_copy_to_scratch().  I'm
> > starting to think that the xdr scratch buffer is fine, and that it's
> > the other pointer passed to memcpy() in that function that's the
> > problem, and the output from this patch will confirm for me.
>
> Oh, and can you add this one on top of the v2 patch as well?

Sorry about the noise today. Can you use this patch instead of the two
I attached earlier? I cleaned up the output and cut down on extra
output..

>
> Thanks,
> Anna
>
> >
> > Thanks,
> > Anna
> >
> > >
> > > Anna
> > > >
> > > > Best regards,
> > > > Krzysztof
> > > >

View attachment "0001-NFS-Add-debugging-printk-s-to-trace-the-READ_PLUS-xd.patch" of type "text/x-patch" (6616 bytes)