[PATCH] realtek: fix locking bug in rtl838x_hw_receive()

[Sander Vanheule]

Hi Birger,

On Fri, 2022-02-18 at 12:01 +0100, Birger Koblitz wrote:
> A Locking bug in the packet receive path was introduced with PR
> #4973. The following patch prevents the driver from locking
> after a few minutes with an endless flow of
> 
> [ 1434.185085] rtl838x-eth 1b00a300.ethernet eth0: Ring contention: r: 0, last
> a28000f4, cur a28000f8
> [ 1434.208971] rtl838x-eth 1b00a300.ethernet eth0: Ring contention: r: 0, last
> a28000f4, cur a28000fc
> [ 1434.794800] rtl838x-eth 1b00a300.ethernet eth0: Ring contention: r: 0, last
> a28000f4, cur a28000fc
> [ 1435.049187] rtl838x-eth 1b00a300.ethernet eth0: Ring contention: r: 0, last
> a28000f4, cur a28000fc
> 
> Signed-off-by: Bjørn Mork <bjorn at mork.no>
> Signed-off-by: Birger Koblitz <mail at birger-koblitz.de>

If Bjørn signed off on this patch first, he should be the patch author too.
(i.e. start this patch with a From: line). This patch sounds like it should have
a Fixes: tag as well; if you can find out which patch introduced it.

Best,
Sander

> ---
>  .../realtek/files-5.10/drivers/net/ethernet/rtl838x_eth.c  | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/target/linux/realtek/files-
> 5.10/drivers/net/ethernet/rtl838x_eth.c b/target/linux/realtek/files-
> 5.10/drivers/net/ethernet/rtl838x_eth.c
> index ab4a03550bd8..cf6aabc6142f 100644
> --- a/target/linux/realtek/files-5.10/drivers/net/ethernet/rtl838x_eth.c
> +++ b/target/linux/realtek/files-5.10/drivers/net/ethernet/rtl838x_eth.c
> @@ -1254,8 +1254,9 @@ static int rtl838x_hw_receive(struct net_device *dev,
> int r, int budget)
>         bool dsa = netdev_uses_dsa(dev);
>         struct dsa_tag tag;
> 
> -       last = (u32 *)KSEG1ADDR(sw_r32(priv->r->dma_if_rx_cur + r * 4));
>         pr_debug("----------------------------------------------------------
> RX - %d\n", r);
> +       spin_lock_irqsave(&priv->lock, flags);
> +       last = (u32 *)KSEG1ADDR(sw_r32(priv->r->dma_if_rx_cur + r * 4));
> 
>         do {
>                 if ((ring->rx_r[r][ring->c_rx[r]] & 0x1)) {
> @@ -1329,7 +1330,6 @@ static int rtl838x_hw_receive(struct net_device *dev,
> int r, int budget)
>                 }
> 
>                 /* Reset header structure */
> -               spin_lock_irqsave(&priv->lock, flags);
>                 memset(h, 0, sizeof(struct p_hdr));
>                 h->buf = data;
>                 h->size = RING_BUFFER;
> @@ -1338,12 +1338,13 @@ static int rtl838x_hw_receive(struct net_device *dev,
> int r, int budget)
>                         | (ring->c_rx[r] == (priv->rxringlen - 1) ? WRAP :
> 0x1);
>                 ring->c_rx[r] = (ring->c_rx[r] + 1) % priv->rxringlen;
>                 last = (u32 *)KSEG1ADDR(sw_r32(priv->r->dma_if_rx_cur + r *
> 4));
> -               spin_unlock_irqrestore(&priv->lock, flags);
>         } while (&ring->rx_r[r][ring->c_rx[r]] != last && work_done < budget);
> 
>         // Update counters
>         priv->r->update_cntr(r, 0);
> 
> +       spin_unlock_irqrestore(&priv->lock, flags);
> +
>         return work_done;
>  }
>