On Thu, 6 Mar 2014, Dan Williams wrote: > >>> Mapped at: > >>> [<c13081b5>] debug_dma_alloc_coherent+0x2b/0xc3 > >>> [<c116fcee>] dma_pool_alloc+0x14f/0x2fd > >>> [<c1456eaa>] uhci_alloc_td.isra.35+0x24/0x60 > >>> [<c1457fa6>] uhci_start+0x272/0x56b > >>> [<c142d8fb>] usb_add_hcd+0x252/0x774 > >> > >> I don't get it. As the name indicates, debug_dma_alloc_coherent should > >> give us consistent memory -- meaning that the CPU is allowed to access > >> the memory while DMA is in progress, without worrying about caching > >> effects (see Documentation/DMA-API.txt). > >> > >> So why should we get a warning when the CPU accesses this memory? Is > >> this a regression in the DMA debug library? > > > > Yes, it seems so. alloc_coherent needs to be exempt from active > > mapping tracking. Fix coming up. > > > > Actually I'm not so sure. Yes, alloc_coherent means the cpu can > touch, but if that page is COW'd how can you be sure that the copy > gets the most up to date data from the device? This check is > asserting that dma might be colliding with a copy-on-write event. dma_pool_create should never return memory that requires COW. How would the system know when to do the copies? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
