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

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Message-ID: <ZwzPDU5Lgt6MbpYt@fedora>
Date: Mon, 14 Oct 2024 15:58:05 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Christoph Hellwig <hch@....de>
Cc: 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 Mon, Oct 14, 2024 at 09:41:51AM +0200, Christoph Hellwig wrote:
> On Mon, Oct 14, 2024 at 09:23:14AM +0200, Hannes Reinecke wrote:
> >> 3) some storage utilities
> >> - dm thin provisioning utility of thin_check
> >> - `dt`(https://github.com/RobinTMiller/dt)
> >>
> >> I looks like same user buffer is used in more than 1 dio.
> >>
> >> 4) some self cooked test code which does same thing with 1)
> >>
> >> In storage stack, the buffer provider is far away from the actual DMA
> >> controller operating code, which doesn't have the knowledge if
> >> DMA_ATTR_SKIP_CPU_SYNC should be set.
> >>
> >> And suggestions for avoiding this noise?
> >>
> > Can you check if this is the NULL page? Operations like 'discard' will 
> > create bios with several bvecs all pointing to the same NULL page.
> > That would be the most obvious culprit.
> 
> 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.


Thanks,
Ming