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

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Date:   Sat, 17 Jun 2023 12:09:45 +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 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.


Best regards,
Krzysztof

View attachment "oops-nfs-read-plus-20230617.txt" of type "text/plain" (106344 bytes)