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

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Date:   Wed, 14 Jun 2023 16:55:17 -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)

Hi Krzysztof,

On Sat, Jun 10, 2023 at 6:15 AM Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> wrote:
>
> On 06/03/2023 18:09, Anna Schumaker wrote:
> > Hi Krzysztof,
> >
> > On Tue, Feb 14, 2023 at 6:02 AM Krzysztof Kozlowski
> > <krzysztof.kozlowski@...aro.org> wrote:
> >>
> >> On 12/02/2023 15:05, Anna Schumaker wrote:
> >>>>> From ac2d6c501dbcdb306480edaee625b5496f1fb4f5 Mon Sep 17 00:00:00 2001
> >>>>> From: Anna Schumaker <Anna.Schumaker@...app.com>
> >>>>> Date: Fri, 10 Feb 2023 15:50:22 -0500
> >>>>> Subject: [PATCH] NFSv4.2: Rework scratch handling for READ_PLUS
> >>>>>
> >>>>
> >>>> Patch is corrupted - maybe mail program reformatted it when sending:
> >>>>
> >>>> Applying: NFSv4.2: Rework scratch handling for READ_PLUS
> >>>> error: corrupt patch at line 12
> >>>> Patch failed at 0001 NFSv4.2: Rework scratch handling for READ_PLUS
> >>>
> >>> That's weird. I wasn't expecting gmail to reformat the patch but I
> >>> guess it did. I've added it as an attachment so that shouldn't happen
> >>> again.
> >>
> >> 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.

Thanks,
Anna

>
> Best regards,
> Krzysztof
>

View attachment "0001-NFS-Add-debugging-printk-s-to-trace-the-xdr-scratch-.patch" of type "text/x-patch" (2716 bytes)