Re: [PATCH] generic/391: check inode metadata on f{data}sync after power-cut

Eryu Guan
2016-11-17T16:58:42Z

On Thu, Nov 17, 2016 at 11:32:03AM -0500, Brian Foster wrote:
[snip some unrelated context]
> > > > > +{
> > > > > + src/godown $SCRATCH_MNT >> $seqres.full
> > > > > + $XFS_IO_PROG -r -c "stat -v" $1 >$tmp.before
> > > >
> > > > Shouldn't we call godown *after* xfs_io -c stat? I saw EIO on this
> > > > xfs_io command and all sub-tests reported stat diff.
> > > >
> > >
> > > Yeah.. I haven't run the test, but I would expect pretty much anything
> > > to return an error after an fs shutdown.
> > >
> > > > And perhaps we need to flush the log on godown for XFS? i.e.
> > > >
> > > > src/godown -f $SCRATCH_MNT >> $seqres.full
> > > >
> > >
> > > I don't think this is necessary. The semantics of fsync() dictate that
> > > the fs do what is necessary to make the file persistent on disk. This
> > > means it is the fs responsibility to ensure the changes are logged on
> > > disk. Indeed, xfs_file_fsync() calls _xfs_log_force_lsn() to flush the
> > > log up to the most recent LSN that covered the inode in question.
> > >
> > > > Otherwise XFS fails all the "1024" & fsync tests (after I fixed the
> > > > godown & xfs_io order locally), fdatasync tests are fine.
> > > >
> > > > @@ -1,8 +1,16 @@
> > > > QA output created by 391
> > > > ==== i_size 1024 test with fsync ====
> > > > +6c6
> > > > +< stat.blocks = 8200
> > > > +---
> > > > +> stat.blocks = 16256
> > > > ==== i_size 4096 test with fsync ====
> > > > ==== i_time test with fsync ====
> > > > ==== fpunch 1024 test with fsync ====
> > > > +6c6
> > > > +< stat.blocks = 8208
> > > > +---
> > > > +> stat.blocks = 24576
> > > > ==== fpunch 4096 test with fsync ====
> > > >
> > > > Not sure if this is the expected behavior on XFS. cc'ed xfs list for
> > > > some inputs.
> > > >
> > >
> > > Am I reading this correctly that you're seeing more blocks than
> > > expected? If so, preallocation perhaps?
> >
> > Yes, you're correct, I see more blocks after godown than before godown.
> >
> > I tried adding "-o allocsize=4k" to MOUNT_OPTIONS, it works but not
> > always. e.g. on a host with sunit/swidth reported from underlying block
> > device, test still fails.
> >
>
> I'm not quite sure where the preallocation is coming from in that case.
> It looks like it should honor allocsize, so that might be worth looking
> into.
>
> > # xfs_info /mnt/xfs
> > meta-data=/dev/mapper/systemvg-testlv2 isize=512 agcount=16, agsize=245696 blks
> > = sectsz=512 attr=2, projid32bit=1
> > = crc=1 finobt=1 spinodes=0 rmapbt=0
> > = reflink=0
> > data = bsize=4096 blocks=3931136, imaxpct=25
> > = sunit=64 swidth=192 blks
> > naming =version 2 bsize=4096 ascii-ci=0 ftype=1
> > log =internal bsize=4096 blocks=2560, version=2
> > = sectsz=512 sunit=64 blks, lazy-count=1
> > realtime =none extsz=4096 blocks=0, rtextents=0
> >
> > Part of the test diff:
> > ==== i_size 1024 test with fsync ====
> > +6c6
> > +< stat.blocks = 8200
> > +---
> > +> stat.blocks = 8704
> >
> > On the other hand, adding "-f" to godown always works for me.
> >
>
> I'm guessing the difference here is that fsync flushes the inode with
> preallocation, but preallocation is typically cleaned up on file close
> (when xfs_io exits). So a subsequent log flush at shutdown may flush
> the transaction that clears out post-eof blocks. Note that it may also
> hit the disk without the log forcing shutdown, it's just not guaranteed
> in that case.
>
> The right thing to do is probably deal with preallocation explicitly in
> the test. E.g., a truncate of the file to the current size after a
> potentially preallocated write, but before the fsync, should always
> result in an equivalent blocks count post-recovery.

You're right, I added truncate operation to isize test and punch test,
and this case passed without problem on XFS. Thanks!

Eryu