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

[Christoph Hellwig]

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?