Re: [PATCH] xfs: fail dax mount if reflink is enabled on a partition

["Darrick J. Wong" <djwong@kernel.org>]

[add tytso to cc since he asked about "How do you actually /get/ fsdax
mode these days?" this morning]

On Tue, Oct 25, 2022 at 10:56:19AM -0700, Darrick J. Wong wrote:
> On Tue, Oct 25, 2022 at 02:26:50PM +0000, ruansy.fnst@fujitsu.com wrote:
> > 
> > 
> > 在 2022/10/24 13:31, Dave Chinner 写道:
> > > On Mon, Oct 24, 2022 at 03:17:52AM +0000, ruansy.fnst@fujitsu.com wrote:
> > >> 在 2022/10/24 6:00, Dave Chinner 写道:
> > >>> On Fri, Oct 21, 2022 at 07:11:02PM -0700, Darrick J. Wong wrote:
> > >>>> On Thu, Oct 20, 2022 at 10:17:45PM +0800, Yang, Xiao/杨 晓 wrote:
> > >>>>> In addition, I don't like your idea about the test change because it will
> > >>>>> make generic/470 become the special test for XFS. Do you know if we can fix
> > >>>>> the issue by changing the test in another way? blkdiscard -z can fix the
> > >>>>> issue because it does zero-fill rather than discard on the block device.
> > >>>>> However, blkdiscard -z will take a lot of time when the block device is
> > >>>>> large.
> > >>>>
> > >>>> Well we /could/ just do that too, but that will suck if you have 2TB of
> > >>>> pmem. ;)
> > >>>>
> > >>>> Maybe as an alternative path we could just create a very small
> > >>>> filesystem on the pmem and then blkdiscard -z it?
> > >>>>
> > >>>> That said -- does persistent memory actually have a future?  Intel
> > >>>> scuttled the entire Optane product, cxl.mem sounds like expansion
> > >>>> chassis full of DRAM, and fsdax is horribly broken in 6.0 (weird kernel
> > >>>> asserts everywhere) and 6.1 (every time I run fstests now I see massive
> > >>>> data corruption).
> > >>>
> > >>> Yup, I see the same thing. fsdax was a train wreck in 6.0 - broken
> > >>> on both ext4 and XFS. Now that I run a quick check on 6.1-rc1, I
> > >>> don't think that has changed at all - I still see lots of kernel
> > >>> warnings, data corruption and "XFS_IOC_CLONE_RANGE: Invalid
> > >>> argument" errors.
> > >>
> > >> Firstly, I think the "XFS_IOC_CLONE_RANGE: Invalid argument" error is
> > >> caused by the restrictions which prevent reflink work together with DAX:
> > >>
> > >> a. fs/xfs/xfs_ioctl.c:1141
> > >> /* Don't allow us to set DAX mode for a reflinked file for now. */
> > >> if ((fa->fsx_xflags & FS_XFLAG_DAX) && xfs_is_reflink_inode(ip))
> > >>          return -EINVAL;
> > >>
> > >> b. fs/xfs/xfs_iops.c:1174
> > >> /* Only supported on non-reflinked files. */
> > >> if (xfs_is_reflink_inode(ip))
> > >>          return false;
> > >>
> > >> These restrictions were removed in "drop experimental warning" patch[1].
> > >>    I think they should be separated from that patch.
> > >>
> > >> [1]
> > >> https://lore.kernel.org/linux-xfs/1663234002-17-1-git-send-email-ruansy.fnst@fujitsu.com/
> > >>
> > >>
> > >> Secondly, how the data corruption happened?
> > > 
> > > No idea - i"m just reporting that lots of fsx tests failed with data
> > > corruptions. I haven't had time to look at why, I'm still trying to
> > > sort out the fix for a different data corruption...
> > > 
> > >> Or which case failed?
> > > 
> > > *lots* of them failed with kernel warnings with reflink turned off:
> > > 
> > > SECTION       -- xfs_dax_noreflink
> > > =========================
> > > Failures: generic/051 generic/068 generic/075 generic/083
> > > generic/112 generic/127 generic/198 generic/231 generic/247
> > > generic/269 generic/270 generic/340 generic/344 generic/388
> > > generic/461 generic/471 generic/476 generic/519 generic/561 xfs/011
> > > xfs/013 xfs/073 xfs/297 xfs/305 xfs/517 xfs/538
> > > Failed 26 of 1079 tests
> > > 
> > > All of those except xfs/073 and generic/471 are failures due to
> > > warnings found in dmesg.
> > > 
> > > With reflink enabled, I terminated the run after g/075, g/091, g/112
> > > and generic/127 reported fsx data corruptions and g/051, g/068,
> > > g/075 and g/083 had reported kernel warnings in dmesg.
> > > 
> > >> Could
> > >> you give me more info (such as mkfs options, xfstests configs)?
> > > 
> > > They are exactly the same as last time I reported these problems.
> > > 
> > > For the "no reflink" test issues:
> > > 
> > > mkfs options are "-m reflink=0,rmapbt=1", mount options "-o
> > > dax=always" for both filesytems.  Config output at start of test
> > > run:
> > > 
> > > SECTION       -- xfs_dax_noreflink
> > > FSTYP         -- xfs (debug)
> > > PLATFORM      -- Linux/x86_64 test3 6.1.0-rc1-dgc+ #1615 SMP PREEMPT_DYNAMIC Wed Oct 19 12:24:16 AEDT 2022
> > > MKFS_OPTIONS  -- -f -m reflink=0,rmapbt=1 /dev/pmem1
> > > MOUNT_OPTIONS -- -o dax=always -o context=system_u:object_r:root_t:s0 /dev/pmem1 /mnt/scratch
> > > 
> > > pmem devices are a pair of fake 8GB pmem regions set up by kernel
> > > CLI via "memmap=8G!15G,8G!24G". I don't have anything special set up
> > > - the kernel config is kept minimal for these VMs - and the only
> > > kernel debug option I have turned on for these specific test runs is
> > > CONFIG_XFS_DEBUG=y.
> > 
> > Thanks for the detailed info.  But, in my environment (and my 
> > colleagues', and our real server with DCPMM) these failure cases (you 
> > mentioned above, in dax+non_reflink mode, with same test options) cannot 
> > reproduce.
> > 
> > Here's our test environment info:
> >   - Ruan's env: fedora 36(v6.0-rc1) on kvm,pmem 2x4G:file backended
> >   - Yang's env: fedora 35(v6.1-rc1) on kvm,pmem 2x1G:memmap=1G!1G,1G!2G
> >   - Server's  : Ubuntu 20.04(v6.0-rc1) real machine,pmem 2x4G:real DCPMM
> > 
> > (To quickly confirm the difference, I just ran the failed 26 cases you 
> > mentioned above.)  Except for generic/471 and generic/519, which failed 
> > even when dax is off, the rest passed.
> > 
> > 
> > We don't want fsdax to be truned off.  Right now, I think the most 
> > important thing is solving the failed cases in dax+non_reflink mode. 
> > So, firstly, I have to reproduce those failures.  Is there any thing 
> > wrong with my test environments?  I konw you are using 'memmap=XXG!YYG' to 
> > simulate pmem.  So, (to Darrick) could you show me your config of dev 
> > environment and the 'testcloud'(I am guessing it's a server with real 
> > nvdimm just like ours)?
> 
> Nope.  Since the announcement of pmem as a product, I have had 15
> minutes of acces to one preproduction prototype server with actual
> optane DIMMs in them.
> 
> I have /never/ had access to real hardware to test any of this, so it's
> all configured via libvirt to simulate pmem in qemu:
> https://lore.kernel.org/linux-xfs/YzXsavOWMSuwTBEC@magnolia/
> 
> /run/mtrdisk/[gh].mem are both regular files on a tmpfs filesystem:
> 
> $ grep mtrdisk /proc/mounts
> none /run/mtrdisk tmpfs rw,relatime,size=82894848k,inode64 0 0
> 
> $ ls -la /run/mtrdisk/[gh].mem
> -rw-r--r-- 1 libvirt-qemu kvm 10739515392 Oct 24 18:09 /run/mtrdisk/g.mem
> -rw-r--r-- 1 libvirt-qemu kvm 10739515392 Oct 24 19:28 /run/mtrdisk/h.mem

Also forgot to mention that the VM with the fake pmem attached has a
script to do:

ndctl create-namespace --mode fsdax --map dev -e namespace0.0 -f
ndctl create-namespace --mode fsdax --map dev -e namespace1.0 -f

Every time the pmem device gets recreated, because apparently that's the
only way to get S_DAX mode nowadays?

--D

> --D
> 
> > 
> > 
> > (I just found I only tested on 4G and smaller pmem device.  I'll try the 
> > test on 8G pmem)
> > 
> > > 
> > > THe only difference between the noreflink and reflink runs is that I
> > > drop the "-m reflink=0" mkfs parameter. Otherwise they are identical
> > > and the errors I reported are from back-to-back fstests runs without
> > > rebooting the VM....
> > > 
> > > -Dave.
> > 
> > 
> > --
> > Thanks,
> > Ruan.