linux-kernel - Re: [Report] annoyed dma debug warning "cacheline tracking EEXIST, overlapping mappings aren't supported"

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Message-ID: <20241015075418.GA25487@lst.de>
Date: Tue, 15 Oct 2024 09:54:18 +0200
From: Christoph Hellwig <hch@....de>
To: Ming Lei <ming.lei@...hat.com>
Cc: Christoph Hellwig <hch@....de>, Robin Murphy <robin.murphy@....com>,
	Hannes Reinecke <hare@...e.de>,
	Hamza Mahfooz <someguy@...ective-light.com>,
	Dan Williams <dan.j.williams@...el.com>,
	linux-block@...r.kernel.org, io-uring@...r.kernel.org,
	linux-raid@...r.kernel.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [Report] annoyed dma debug warning "cacheline tracking EEXIST,
 overlapping mappings aren't supported"

On Tue, Oct 15, 2024 at 03:40:26PM +0800, Ming Lei wrote:
> > Yes, active_cacheline_insert only complains for FROM_DEVICE or
> > BIDIRECTIONAL mappings.  I can't see how raid 1 would trigger that
> > given that it only reads from one leg at a time.
> > 
> > Ming, can you look a bit more into what is happening here?
> 
> All should be READ IO which is FROM_DEVICE, please see my reply:

Yes, reads translate to DMA_FROM_DEVICE.

> https://lore.kernel.org/linux-block/Zw3MZrK_l7DuFfFd@fedora/
> 
> And the raid1 warning is actually from raid1_sync_request().

In that case the warnings are perfectly valid because the I/O patterns
will create data corruption on non-coherent architectures.  For direct
I/O from userspace the kernel can't prevent it, but for raid1 we should
be able to do something better.  As raid1_sync_request is a convoluted
and undocumented mess I don't have a straigh shot answer to what it is
doing (wrong) and how to fix it unfortunately.

> 
> 
> Thanks,
> Ming
---end quoted text---