Re: [PATCH v2 2/7] dax: change bdev_dax_supported() to support boolean returns

[Mike Snitzer <snitzer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Mon, Jun 04 2018 at  7:40pm -0400,
Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:

> On Sun, Jun 3, 2018 at 6:48 PM, Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:
> > On Sun, Jun 3, 2018 at 5:25 PM, Dave Chinner <david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org> 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-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org> 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.

Dave, _this_ is when you know you've arrived! ;)