Re: XFS kernel BUG during generic/270 with v4.10

[Brian Foster <bfoster@redhat.com>]

On Thu, Mar 02, 2017 at 08:47:01AM -0800, Darrick J. Wong wrote:
> On Thu, Mar 02, 2017 at 11:29:34AM -0500, Brian Foster wrote:
> > On Wed, Feb 22, 2017 at 12:13:00PM -0700, Ross Zwisler wrote:
> > > By running generic/270 in a loop on an XFS filesystem mounted with DAX I'm
> > > able to reliably generate the following kernel bug after a few (~10)
> > > iterations (output passed through kasan_symbolize.py):
> > > 
> > > run fstests generic/270 at 2017-02-22 12:01:05
> > > XFS (pmem0p2): Unmounting Filesystem
> > > XFS (pmem0p2): DAX enabled. Warning: EXPERIMENTAL, use at your own risk
> > > XFS (pmem0p2): Mounting V5 Filesystem
> > > XFS (pmem0p2): Ending clean mount
> > > XFS (pmem0p2): Quotacheck needed: Please wait.
> > > XFS (pmem0p2): Quotacheck: Done.
> > > XFS (pmem0p2): xlog_verify_grant_tail: space > BBTOB(tail_blocks)
> > > XFS: Assertion failed: XFS_FORCED_SHUTDOWN(ip->i_mount) || ip->i_delayed_blks == 0, file: fs/xfs/xfs_super.c, line: 965
> > 
> > This means we've reclaimed an inode that still has delayed allocation
> > blocks, which shouldn't occur. We do have one recent fix in this area:
> > fa7f138 ("xfs: clear delalloc and cache on buffered write failure"). Do
> > you still reproduce this? If so, does it reproduce with that patch?
> > 
> > > ------------[ cut here ]------------
> > ...
> > > ---[ end trace 384d06985052f068 ]---
> > > 
> > > Here's the xfstests run:
> > > 
> > > FSTYP         -- xfs (debug)
> > > PLATFORM      -- Linux/x86_64 alara 4.10.0
> > > MKFS_OPTIONS  -- -f -bsize=4096 /dev/pmem0p2
> > > MOUNT_OPTIONS -- -o dax -o context=system_u:object_r:nfs_t:s0 /dev/pmem0p2 /mnt/xfstests_scratch
> > > 
> > > generic/270 24s ..../check: line 596: 15817 Segmentation fault      ./$seq > $tmp.rawout 2>&1
> > >  [failed, exit status 139] - output mismatch (see /root/xfstests/results//generic/270.out.bad)
> > >     --- tests/generic/270.out	2016-10-21 15:31:10.568945780 -0600
> > >     +++ /root/xfstests/results//generic/270.out.bad	2017-02-22 12:01:29.272718284 -0700
> > >     @@ -3,6 +3,3 @@
> > >      Run fsstress
> > >      
> > >      Run dd writers in parallel
> > >     -Comparing user usage
> > >     -Comparing group usage
> > >     -Comparing filesystem consistency
> > >     ...
> > >     (Run 'diff -u tests/generic/270.out /root/xfstests/results//generic/270.out.bad'  to see the entire diff)
> > > 
> > > This was done in my normal test setup, which is a pair of PMEM disks that
> > > enable DAX.
> > > 
> > 
> > What I'm a little confused about though is that I thought DAX meant we
> > bypassed buffered I/O and always used direct I/O (which means you should
> > never perform delayed allocation). :/
> 
> The block devices are pmem, but I don't think g/270 does anything
> special to turn on DAX (the inode flag) for the files it's writing.
> 

Doesn't the dax mount force the inode flag?

Brian

> --D
> 
> > 
> > Brian
> > 
> > > Here are the versions of xfstests and xfsprogs that I'm using:
> > > 
> > > xfstets: f438604 generic: test mmap io through DAX and non-DAX
> > > 
> > > xfsprogs: xfs_admin version 4.9.0
> > > This is just the xfsprogs that comes packaged with Fedora 25.
> > > 
> > > Thanks,
> > > - Ross
> > > --
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