Re: Kernel Panic in skb_release_data using genet

On 6/2/2021 6:28 AM, Maxime Ripard wrote:

On Tue, Jun 01, 2021 at 11:33:18AM +0200, nicolas saenz julienne wrote:

quoted

On Mon, 2021-05-31 at 19:36 -0700, Florian Fainelli wrote:

quoted

quoted

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