Re: Kernel Panic in skb_release_data using genet

[Florian Fainelli]

On 5/28/2021 9:48 AM, Florian Fainelli wrote:
> On 5/28/21 9:32 AM, Maxime Ripard wrote:
>> hi Florian,
>>
>> On Fri, May 28, 2021 at 09:21:27AM -0700, Florian Fainelli wrote:
>>> On 5/24/21 8:37 AM, Florian Fainelli wrote:
>>>>
>>>>
>>>> On 5/24/2021 8:13 AM, Maxime Ripard wrote:
>>>>> Hi Florian,
>>>>>
>>>>> On Mon, May 24, 2021 at 07:49:25AM -0700, Florian Fainelli wrote:
>>>>>> Hi Maxime,
>>>>>>
>>>>>> On 5/24/2021 6:01 AM, Maxime Ripard wrote:
>>>>>>> Hi Doug, Florian,
>>>>>>>
>>>>>>> I've been running a RaspberryPi4 with a mainline kernel for a while,
>>>>>>> booting from NFS. Every once in a while (I'd say ~20-30% of all boots),
>>>>>>> I'm getting a kernel panic around the time init is started.
>>>>>>>
>>>>>>> I was debugging a kernel based on drm-misc-next-2021-05-17 today with
>>>>>>> KASAN enabled and got this, which looks related:
>>>>>>
>>>>>> Is there a known good version that could be used for bisection or you
>>>>>> just started to do this test and you have no reference point?
>>>>>
>>>>> I've had this issue for over a year and never (I think?) got a good
>>>>> version, so while it might be a regression, it's not a recent one.
>>>>
>>>> OK, this helps and does not really help.
>>>>
>>>>>
>>>>>> How stable in terms of clocking is the configuration that you are using?
>>>>>> I could try to fire up a similar test on a Pi4 at home, or use one of
>>>>>> our 72112 systems which is the closest we have to a Pi4 and see if that
>>>>>> happens there as well.
>>>>>
>>>>> I'm not really sure about the clocking. Is there any clock you want to
>>>>> look at in particular?
>>>>
>>>> ARM, DDR, AXI, anything that could cause some memory corruption to occur
>>>> essentially. GENET clocks are fairly fixed, you have a 250MHz clock and
>>>> a 125MHz clock feeding the data path.
>>>>
>>>>>
>>>>> My setup is fairly simple: the firmware and kernel are loaded over TFTP
>>>>> and the rootfs is mounted over NFS, and the crash always occur around
>>>>> init start, so I guess when it actually starts to transmit a decent
>>>>> amount of data?
>>>>
>>>> Do you reproduce this problem with KASAN disabled, do you eventually
>>>> have a crash pointing back to the same location?
>>>>
>>>> I have a suspicion that this is all Pi4 specific because we regularly
>>>> run the GENET driver through various kernel versions (4.9, 5.4 and 5.10
>>>> and mainline) and did not run into that.
>>>
>>> I have not had time to get a set-up to reproduce what you are seeing,
>>> could you share your .config meanwhile? Thanks
>>
>> Sorry, I didn't have the time to check how the clock were behaving.
>>
>> You'll find attached my config.txt file and .config
>>
>> I'm booting the board entirely from TFTP (which might introduce some
>> issues in the "handoff" from the bootloader to the kernel), you'll find
>> some guide there:
>>
>> https://www.raspberrypi.org/documentation/hardware/raspberrypi/bootmodes/net_tutorial.md
> 
> That is also how I boot my Pi4 at home, and I suspect you are right, if
> the VPU does not shut down GENET's DMA, and leaves buffer addresses in
> the on-chip descriptors that point to an address space that is managed
> totally differently by Linux, then we can have a serious problem and
> create some memory corruption when the ring is being reclaimed. I will
> run a few experiments to test that theory and there may be a solution
> using the SW_INIT reset controller to have a big reset of the controller
> before handing it over to the Linux driver.

Adding a WARN_ON(reg & DMA_EN) in bcmgenet_dma_disable() has not shown
that the TX or RX DMA have been left running during the hand over from
the VPU to the kernel. I checked out drm-misc-next-2021-05-17 to reduce
as much as possible the differences between your set-up and my set-up
but so far have not been able to reproduce the crash in booting from NFS
repeatedly, I will try again.
-- 
Florian