Ming Lei wrote: > On Mon, Oct 14, 2024 at 07:09:08PM +0100, Robin Murphy wrote: > > On 14/10/2024 8:58 am, Ming Lei wrote: > > > 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. > > > > 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. > > The two io_uring tests are READ, and the dm thin_check are READ too. "READ from the device" == "WRITE to the page" (DMA_FROM_DEVICE). > For the raid1 case, the warning is from raid1_sync_request() which may > have both READ/WRITE IO. I don't see an easy way out of this without instrumenting archs that can not support overlapping mappings to opt-in to bounce buffering for these cases. Archs that can support this can skip the opt-in and quiet this test, but some of the value is being able to catch boundary conditions on more widely available systems.
