linux-kernel - Re: DPAA2 triggers, [PATCH] dma debug: report -EEXIST errors in add_dma

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Date:   Fri, 1 Oct 2021 09:21:13 +0000
From:   Ioana Ciornei <ioana.ciornei@....com>
To:     Christoph Hellwig <hch@....de>
CC:     Jeremy Linton <jeremy.linton@....com>,
        Hamza Mahfooz <someguy@...ective-light.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: DPAA2 triggers, [PATCH] dma debug: report -EEXIST errors in
 add_dma_entry

On Fri, Oct 01, 2021 at 06:19:59AM +0200, Christoph Hellwig wrote:
> On Tue, Sep 14, 2021 at 03:45:06PM +0000, Ioana Ciornei wrote:
> > [  245.927020] fsl_dpaa2_eth dpni.3: scather-gather idx 0 P=20a7320000 N=20a7320 D=20a7320000 L=30 DMA_BIDIRECTIONAL dma map error check not applicable·
> > [  245.927048] fsl_dpaa2_eth dpni.3: scather-gather idx 1 P=20a7320030 N=20a7320 D=20a7320030 L=5a8 DMA_BIDIRECTIONAL dma map error check not applicable
> > [  245.927062] DMA-API: cacheline tracking EEXIST, overlapping mappings aren't supported
> > 
> > The first line is the dump of the dma_debug_entry which is already present
> > in the radix tree and the second one is the entry which just triggered
> > the EEXIST.
> > 
> > As we can see, they are not actually overlapping, at least from my
> > understanding. The first one starts at 0x20a7320000 with a size 0x30
> > and the second one at 0x20a7320030.
> 
> They overlap the cache lines.  Which means if you use this driver
> on a system that is not dma coherent you will corrupt data.

This is a driver of an integrated ethernet controller which is DMA
coherent.

I added a print just to make sure of this:

--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -567,6 +567,7 @@ static void add_dma_entry(struct dma_debug_entry *entry)
                pr_err("cacheline tracking ENOMEM, dma-debug disabled\n");
                global_disable = true;
        } else if (rc == -EEXIST) {
+               pr_err("dev_is_dma_coherent(%s) = %d\n", dev_name(entry->dev), dev_is_dma_coherent(entry->dev));
                err_printk(entry->dev, entry,
                        "cacheline tracking EEXIST, overlapping mappings aren't supported\n");
        }


[   85.852218] DMA-API: dev_is_dma_coherent(dpni.3) = 1
[   85.858891] ------------[ cut here ]------------
[   85.858893] DMA-API: fsl_dpaa2_eth dpni.3: cacheline tracking EEXIST, overlapping mappings aren't supported
[   85.858901] WARNING: CPU: 13 PID: 1046 at kernel/dma/debug.c:571 add_dma_entry+0x330/0x390
[   85.858911] Modules linked in:
[   85.858915] CPU: 13 PID: 1046 Comm: iperf3 Not tainted 5.15.0-rc2-00478-g34286ba6a164-dirty #1275
[   85.858919] Hardware name: NXP Layerscape LX2160ARDB (DT)


Shouldn't this case not generate this kind of warning?

Ioana