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

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Message-ID: <Zw4camcCvclL4Q_6@fedora>
Date: Tue, 15 Oct 2024 15:40:26 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Christoph Hellwig <hch@....de>
Cc: 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 06:54:13AM +0200, Christoph Hellwig wrote:
> On Mon, Oct 14, 2024 at 07:09:08PM +0100, Robin Murphy wrote:
> >>> The only case I fully understand without looking into the details
> >>> is raid1, and that will obviously map the same data multiple times
> >>
> >> The other cases should be concurrent DIOs on same userspace buffer.
> >
> > active_cacheline_insert() does already bail out for DMA_TO_DEVICE, so it 
> > returning -EEXIST to tickle the warning would seem to genuinely imply these 
> > are DMA mappings requesting to *write* the same cacheline concurrently, 
> > which is indeed broken in general.
> 
> 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:

https://lore.kernel.org/linux-block/Zw3MZrK_l7DuFfFd@fedora/

And the raid1 warning is actually from raid1_sync_request().


Thanks,
Ming