On Fri, 30 Sep 2022 14:46:06 +0100 Robin Murphy wrote: > On 2022-09-30 14:10, Marek Behún wrote: > > Hello Linus, Arnd, Robin and Christoph, > > > > I just bisected a regression on Turris Omnia (Armada 385), wherein the > > system hangs shortly after init is run, to commit > > > > ae626eb97376 ("ARM/dma-mapping: use dma-direct unconditionally") > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ae626eb97376 > > > > In order to fix the regression, I had to revert this commit and > > subsequent 3 commits: > > ae626eb97376 ("ARM/dma-mapping: use dma-direct unconditionally") > > 42998ef08aba ("ARM/dma-mapping: drop .dma_supported for IOMMU ops") > > d563bccfa35b ("ARM/dma-mapping: consolidate IOMMU ops callbacks") > > 4136ce90f079 ("ARM/dma-mapping: merge IOMMU ops") > > in reverse order, of course: > > git revert 4136ce90f079 > > git revert d563bccfa35b > > git revert 42998ef08aba > > git revert ae626eb97376 > > > > Christoph, Robin, since you are the authors of these commits, do you > > have any idea what could be happening? Are we able to fix this without > > reverting those commits, before 6.0? > > "hangs shortly after init" isn't much to go on. Are any errors logged? > Possibly some driver is sat waiting for a DMA transfer to complete, that > has somehow got the wrong address or lost coherency so never gets seen, > but without at least being able to narrow it down to the affected driver > it's hard to do much more than vague guessing. OK I enabled CONFIG_DMA_API_DEBUG and now am getting a null pointer dereference. I managed to isolate the bug to a specifc line in mvneta driver: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/ethernet/marvell/mvneta.c#n2591 I put debug printfs (pr_err(" a %i\n", __LINE__)) into the mvneta_rx_hwbm() function. The pr_err after the call to dma_sync_single_range_for_cpu() prints, but the pr_err after skb_put_data() does not print. Attaching console output. Marek