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

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Date:   Mon, 24 Oct 2022 16:31:09 +1100
From:   Dave Chinner <david@...morbit.com>
To:     "ruansy.fnst@...itsu.com" <ruansy.fnst@...itsu.com>
Cc:     "Darrick J. Wong" <djwong@...nel.org>,
        "yangx.jy@...itsu.com" <yangx.jy@...itsu.com>,
        "Yasunori Gotou (Fujitsu)" <y-goto@...itsu.com>,
        Brian Foster <bfoster@...hat.com>,
        "hch@...radead.org" <hch@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "zwisler@...nel.org" <zwisler@...nel.org>,
        Jeff Moyer <jmoyer@...hat.com>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>,
        "toshi.kani@....com" <toshi.kani@....com>
Subject: Re: [PATCH] xfs: fail dax mount if reflink is enabled on a partition

On Mon, Oct 24, 2022 at 03:17:52AM +0000, ruansy.fnst@...itsu.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.

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.
-- 
Dave Chinner
david@...morbit.com