On Mon, Apr 03, 2017 at 12:37:51PM +0100, Will Deacon wrote: > On Mon, Apr 03, 2017 at 11:56:29AM +0100, Mark Rutland wrote: > > On Fri, Mar 31, 2017 at 06:58:45PM +0100, Mark Rutland wrote: > > > Hi, > > > > > > I'm seeing intermittent bad page state splats on arm64 with 4.11-rc3 and > > > v4.11-rc4. I have not tested earlier kernels, or other architectures. > > > > > > So far, it looks like the flags are always bad in the same > > > way: > > > > > > bad because of flags: 0x80(waiters) > > > > > > ... though I don't know if that's definitely the case for splat 4, the > > > BUG at mm/page_alloc.c:800. > > > > > > I see this in QEMU VMs launched by Syzkaller, triggering once every few > > > hours. So far, I have not been able to reproduce the issue in any other > > > way (including using syz-repro). > > > > It looks like this may be an issue with the arm64 HUGETLB code. > > > > I wasn't able to trigger the issue over the weekend on a kernel with > > HUGETLBFS disabled. There are known issues with our handling of > > contiguous entries, and this might be an artefact of that. > > After chatting with Punit, it looks like this might be because the GUP > code doesn't handle huge ptes (which we create using the contiguous hint), > so follow_page_pte ends up with one of those and goes wrong. In particular, > the migration code will certainly do the wrong thing. > > I'll probably revert the contiguous support (again) if testing indicates > that it makes this issue disappear. It might be worth checking with Punit's patches as well: https://marc.info/?l=linux-arm-kernel&m=149089199018167&w=2 -- Catalin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
