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    SubjectRe: Kernel Panic in skb_release_data using genet
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    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);
    --
    Florian
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