netdev - Re: [PATCH 1/2] net: moxa: do not call dma_unmap

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Message-ID: <Yv6QenTMPkO6gSTI@lunn.ch>
Date:   Thu, 18 Aug 2022 21:18:18 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Sergei Antonov <saproj@...il.com>
Cc:     netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
        Vladimir Oltean <olteanv@...il.com>
Subject: Re: [PATCH 1/2] net: moxa: do not call dma_unmap_single() with null

On Thu, Aug 18, 2022 at 09:29:47PM +0300, Sergei Antonov wrote:
> It fixes a warning during error unwinding:
> 
> WARNING: CPU: 0 PID: 1 at kernel/dma/debug.c:963 check_unmap+0x704/0x980
> DMA-API: moxart-ethernet 92000000.mac: device driver tries to free DMA memory it has not allocated [device address=0x0000000000000000] [size=1600 bytes]
> CPU: 0 PID: 1 Comm: swapper Not tainted 5.19.0+ #60
> Hardware name: Generic DT based system
>  unwind_backtrace from show_stack+0x10/0x14
>  show_stack from dump_stack_lvl+0x34/0x44
>  dump_stack_lvl from __warn+0xbc/0x1f0
>  __warn from warn_slowpath_fmt+0x94/0xc8
>  warn_slowpath_fmt from check_unmap+0x704/0x980
>  check_unmap from debug_dma_unmap_page+0x8c/0x9c
>  debug_dma_unmap_page from moxart_mac_free_memory+0x3c/0xa8
>  moxart_mac_free_memory from moxart_mac_probe+0x190/0x218
>  moxart_mac_probe from platform_probe+0x48/0x88
>  platform_probe from really_probe+0xc0/0x2e4
> 
> Fixes: 6c821bd9edc9 ("net: Add MOXA ART SoCs ethernet driver")
> Signed-off-by: Sergei Antonov <saproj@...il.com>

This looks correct as it is:

Reviewed-by: Andrew Lunn <andrew@...n.ch>

But i do wonder how it go into the situation:

	for (i = 0; i < RX_DESC_NUM; i++) {
		desc = priv->rx_desc_base + i * RX_REG_DESC_SIZE;
		memset(desc, 0, RX_REG_DESC_SIZE);
		moxart_desc_write(RX_DESC0_DMA_OWN, desc + RX_REG_OFFSET_DESC0);
		moxart_desc_write(RX_BUF_SIZE & RX_DESC1_BUF_SIZE_MASK,
		       desc + RX_REG_OFFSET_DESC1);

		priv->rx_buf[i] = priv->rx_buf_base + priv->rx_buf_size * i;
		priv->rx_mapping[i] = dma_map_single(&ndev->dev,
						     priv->rx_buf[i],
						     priv->rx_buf_size,
						     DMA_FROM_DEVICE);
		if (dma_mapping_error(&ndev->dev, priv->rx_mapping[i]))
			netdev_err(ndev, "DMA mapping error\n");

		moxart_desc_write(priv->rx_mapping[i],
		       desc + RX_REG_OFFSET_DESC2 + RX_DESC2_ADDRESS_PHYS);
		moxart_desc_write((uintptr_t)priv->rx_buf[i],
		       desc + RX_REG_OFFSET_DESC2 + RX_DESC2_ADDRESS_VIRT);
	}

There is no way out of this, such that it only allocates some but not
all. So maybe there was an dma_mapping_error, it printed: DMA mapping
error, but kept going? So maybe another patch would be good, making
moxart_mac_setup_desc_ring() return an error when something goes
wrong?

    Andrew