On Mon, Jun 4, 2018 at 8:32 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > [ adding KASAN devs...] > > On Mon, Jun 4, 2018 at 4:40 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: >> On Sun, Jun 3, 2018 at 6:48 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: >>> On Sun, Jun 3, 2018 at 5:25 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: >>>> On Mon, Jun 04, 2018 at 08:20:38AM +1000, Dave Chinner wrote: >>>>> On Thu, May 31, 2018 at 09:02:52PM -0700, Dan Williams wrote: >>>>> > On Thu, May 31, 2018 at 7:24 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: >>>>> > > On Thu, May 31, 2018 at 06:57:33PM -0700, Dan Williams wrote: >>>>> > >> > FWIW, XFS+DAX used to just work on this setup (I hadn't even >>>>> > >> > installed ndctl until this morning!) but after changing the kernel >>>>> > >> > it no longer works. That would make it a regression, yes? >>>>> >>>>> [....] >>>>> >>>>> > >> I suspect your kernel does not have CONFIG_ZONE_DEVICE enabled which >>>>> > >> has the following dependencies: >>>>> > >> >>>>> > >> depends on MEMORY_HOTPLUG >>>>> > >> depends on MEMORY_HOTREMOVE >>>>> > >> depends on SPARSEMEM_VMEMMAP >>>>> > > >>>>> > > Filesystem DAX now has a dependency on memory hotplug? >>>>> >>>>> [....] >>>>> >>>>> > > OK, works now I've found the magic config incantantions to turn >>>>> > > everything I now need on. >>>>> >>>>> By enabling these options, my test VM now has a ~30s pause in the >>>>> boot very soon after the nvdimm subsystem is initialised. >>>>> >>>>> [ 1.523718] Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled >>>>> [ 1.550353] 00:05: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A >>>>> [ 1.552175] Non-volatile memory driver v1.3 >>>>> [ 2.332045] tsc: Refined TSC clocksource calibration: 2199.909 MHz >>>>> [ 2.333280] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x1fb5dcd4620, max_idle_ns: 440795264143 ns >>>>> [ 37.217453] brd: module loaded >>>>> [ 37.225423] loop: module loaded >>>>> [ 37.228441] virtio_blk virtio2: [vda] 10485760 512-byte logical blocks (5.37 GB/5.00 GiB) >>>>> [ 37.245418] virtio_blk virtio3: [vdb] 146800640 512-byte logical blocks (75.2 GB/70.0 GiB) >>>>> [ 37.255794] virtio_blk virtio4: [vdc] 1073741824000 512-byte logical blocks (550 TB/500 TiB) >>>>> [ 37.265403] nd_pmem namespace1.0: unable to guarantee persistence of writes >>>>> [ 37.265618] nd_pmem namespace0.0: unable to guarantee persistence of writes >>>>> >>>>> The system does not appear to be consuming CPU, but it is blocking >>>>> NMIs so I can't get a CPU trace. For a VM that I rely on booting in >>>>> a few seconds because I reboot it tens of times a day, this is a >>>>> problem.... >>>> >>>> And when I turn on KASAN, the kernel fails to boot to a login prompt >>>> because: >>> >>> What's your qemu and kernel command line? I'll take look at this first >>> thing tomorrow. >> >> I was able to reproduce this crash by just turning on KASAN... >> investigating. It would still help to have your config for our own >> regression testing purposes it makes sense for us to prioritize >> "Dave's test config", similar to the priority of not breaking Linus' >> laptop. > > I believe this is a bug in KASAN, or a bug in devm_memremap_pages(), > depends on your point of view. At the very least it is a mismatch of > assumptions. KASAN learns of hot added memory via the memory hotplug > notifier. However, the devm_memremap_pages() implementation is > intentionally limited to the "first half" of the memory hotplug > procedure. I.e. it does just enough to setup the linear map for > pfn_to_page() and initialize the "struct page" memmap, but then stops > short of onlining the pages. This is why we are getting a NULL ptr > deref and not a KASAN report, because KASAN has no shadow area setup > for the linearly mapped pmem range. > > In terms of solving it we could refactor kasan_mem_notifier() so that > devm_memremap_pages() can call it outside of the notifier... I'll give > this a shot. Well, the attached patch got me slightly further, but only slightly... [ 14.998394] BUG: KASAN: unknown-crash in pmem_do_bvec+0x19e/0x790 [nd_pmem] [ 15.000006] Read of size 4096 at addr ffff880200000000 by task systemd-udevd/915 [ 15.001991] [ 15.002590] CPU: 15 PID: 915 Comm: systemd-udevd Tainted: G OE 4.17.0-rc5+ #1 982 [ 15.004783] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.1-0-g0551a 4be2c-prebuilt.qemu-project.org 04/01/2014 [ 15.007652] Call Trace: [ 15.008339] dump_stack+0x9a/0xeb [ 15.009344] print_address_description+0x73/0x280 [ 15.010524] kasan_report+0x258/0x380 [ 15.011528] ? pmem_do_bvec+0x19e/0x790 [nd_pmem] [ 15.012747] memcpy+0x1f/0x50 [ 15.013659] pmem_do_bvec+0x19e/0x790 [nd_pmem] ...I've exhausted my limited kasan internals knowledge, any ideas what it's missing?
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