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Date:   Tue, 6 Jul 2021 10:16:51 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     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

Hi Florian,

On Fri, Jul 02, 2021 at 09:49:31AM -0700, Florian Fainelli wrote:
> 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.

Unfortunately, I haven't spent too much time working on mainline
recently, so I didn't really have the occasion to test further that
patch.

It seems to make sense anyway like you said, so you can definitely send
it, with my Tested-by :)

Maxime

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