On Thu, Apr 17, 2014 at 12:40 AM, Clemens Ladisch <[email protected]> wrote: > poma wrote: >> Sound whispers, > > ??? > >> WARNING: CPU: 3 PID: 900 at lib/dma-debug.c:593 >> debug_dma_assert_idle+0x159/0x1d0() >> snd_hda_intel 0000:00:07.0: DMA-API: cpu touching an active dma mapped >> cacheline [cln=0x03014000] >> ... >> Mapped at: >> [<c074ec12>] debug_dma_alloc_coherent+0x22/0x70 > > "Coherent" means "touching DMA mappings is allowed". > Why does dma-debug complain about that?
Right, but coherency does not follow copy-on-write. The check is there to catch cases where a page is COW'd while an active dma mapping on the source page is present. Sure, the write is coherent, but due to the COW it's going to the wrong page, so you are potentially missing data in the new mapping. See how NET_DMA inspired this check: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/dma/Kconfig?id=77873803363c -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
