linux-kernel - Re: Kernel Panic in skb_release

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Date:   Fri, 2 Jul 2021 09:49:31 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Maxime Ripard <maxime@...no.tech>,
        Florian Fainelli <f.fainelli@...il.com>
Cc:     nicolas saenz julienne <nsaenz@...nel.org>,
        Doug Berger <opendmb@...il.com>,
        bcm-kernel-feedback-list@...adcom.com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: Kernel Panic in skb_release_data using genet

Hey Maxime,

On 6/25/2021 5:59 AM, Maxime Ripard wrote:
> Hi Florian,
> 
> Sorry for the late reply
> 
> On Thu, Jun 10, 2021 at 02:33:17PM -0700, Florian Fainelli wrote:
>> On 6/2/2021 6:28 AM, Maxime Ripard wrote:
>>> On Tue, Jun 01, 2021 at 11:33:18AM +0200, nicolas saenz julienne wrote:
>>>> On Mon, 2021-05-31 at 19:36 -0700, Florian Fainelli wrote:
>>>>>> 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.
>>>>
>>>> FWIW I can reproduce the error too. That said it's rather hard to reproduce,
>>>> something in the order of 1 failure every 20 tries.
>>>
>>> Yeah, it looks like it's only from a cold boot and comes in "bursts",
>>> where you would get like 5 in a row and be done with it for a while.
>>
>> Here are two patches that you could try exclusive from one another
>>
>> 1) Limit GENET to a single queue
>>
>> diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
>> b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
>> index fcca023f22e5..e400c12e6868 100644
>> --- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
>> +++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
>> @@ -3652,6 +3652,12 @@ static int bcmgenet_change_carrier(struct
>> net_device *dev, bool new_carrier)
>>          return 0;
>>   }
>>
>> +static u16 bcmgenet_select_queue(struct net_device *dev, struct sk_buff
>> *skb,
>> +                                struct net_device *sb_dev)
>> +{
>> +       return 0;
>> +}
>> +
>>   static const struct net_device_ops bcmgenet_netdev_ops = {
>>          .ndo_open               = bcmgenet_open,
>>          .ndo_stop               = bcmgenet_close,
>> @@ -3666,6 +3672,7 @@ static const struct net_device_ops
>> bcmgenet_netdev_ops = {
>>   #endif
>>          .ndo_get_stats          = bcmgenet_get_stats,
>>          .ndo_change_carrier     = bcmgenet_change_carrier,
>> +       .ndo_select_queue       = bcmgenet_select_queue,
>>   };
>>
>>   /* Array of GENET hardware parameters/characteristics */
>>
>> 2) Ensure that all TX/RX queues are disabled upon DMA initialization
>>
>> diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
>> b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
>> index fcca023f22e5..7f8a5996fbbb 100644
>> --- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
>> +++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
>> @@ -3237,15 +3237,21 @@ static void bcmgenet_get_hw_addr(struct
>> bcmgenet_priv *priv,
>>   /* Returns a reusable dma control register value */
>>   static u32 bcmgenet_dma_disable(struct bcmgenet_priv *priv)
>>   {
>> +       unsigned int i;
>>          u32 reg;
>>          u32 dma_ctrl;
>>
>>          /* disable DMA */
>>          dma_ctrl = 1 << (DESC_INDEX + DMA_RING_BUF_EN_SHIFT) | DMA_EN;
>> +       for (i = 0; i < priv->hw_params->tx_queues; i++)
>> +               dma_ctrl |= (1 << (i + DMA_RING_BUF_EN_SHIFT));
>>          reg = bcmgenet_tdma_readl(priv, DMA_CTRL);
>>          reg &= ~dma_ctrl;
>>          bcmgenet_tdma_writel(priv, reg, DMA_CTRL);
>>
>> +       dma_ctrl = 1 << (DESC_INDEX + DMA_RING_BUF_EN_SHIFT) | DMA_EN;
>> +       for (i = 0; i < priv->hw_params->rx_queues; i++)
>> +               dma_ctrl |= (1 << (i + DMA_RING_BUF_EN_SHIFT));
>>          reg = bcmgenet_rdma_readl(priv, DMA_CTRL);
>>          reg &= ~dma_ctrl;
>>          bcmgenet_rdma_writel(priv, reg, DMA_CTRL);
> 
> I had a bunch of issues popping up today so I took the occasion to test
> those patches. The first one doesn't change anything, I still had the
> crash occurring with it. With the second applied (in addition), it seems
> like it's fixed. I'll keep testing and will let you know.

Did this patch survive more days of testing? I am tempted to send it 
regardless of your testing because it is a correctness issue that is 
being fixed. There is a global DMA enable bit which should "cut" any 
TX/RX queues, but still, for symmetry with other code paths all queues 
should be disabled.

Thanks!
-- 
Florian