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

[Brian Foster <bfoster@redhat.com>]

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). :/

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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