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

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Message-ID: <dfcc114f-56f1-e4ab-7b36-f9a4ce3e8c8c@linaro.org>
Date:   Wed, 21 Jun 2023 15:27:33 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Anna Schumaker <schumaker.anna@...il.com>
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 21/06/2023 14:49, Anna Schumaker wrote:
> On Sat, Jun 17, 2023 at 6:09 AM Krzysztof Kozlowski
> <krzysztof.kozlowski@...aro.org> wrote:
>>
>> On 15/06/2023 21:38, Anna Schumaker wrote:
>>> 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..
>>>
>>
>> Here you have - attached.
> 
> This is good, thanks! I was finally able to figure out how to hit the
> bug using a 32bit x86 VM, so hopefully the next thing you hear from me
> is a patch fixing the bug!

QEMU also has 32-bit ARM and x86...

Best regards,
Krzysztof