Re: [PATCH] xfs: fix livelock in delayed allocation at ENOSPC

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

On Thu, Apr 27, 2023 at 03:26:00PM +1000, Dave Chinner wrote:
> On Wed, Apr 26, 2023 at 05:53:33PM -0700, Darrick J. Wong wrote:
> > On Thu, Apr 27, 2023 at 10:11:24AM +1000, Dave Chinner wrote:
> > > On Wed, Apr 26, 2023 at 04:38:31PM -0700, Darrick J. Wong wrote:
> > > > I also added a su=128k,sw=4 config to the fstests fleet and am now
> > > > trying to fix all the fstests bugs that produce incorrect test failures.
> > > 
> > > The other thing I noticed is a couple of the FIEMAP tests fail
> > > because they find data blocks where they expect holes such as:
> > > 
> > > generic/225 21s ... - output mismatch (see /home/dave/src/xfstests-dev/results//xfs_align/generic/225.out.bad)
> > >     --- tests/generic/225.out   2022-12-21 15:53:25.479044361 +1100
> > >     +++ /home/dave/src/xfstests-dev/results//xfs_align/generic/225.out.bad      2023-04-26 04:24:31.426016818 +1000
> > >     @@ -1,3 +1,79 @@
> > >      QA output created by 225
> > >      fiemap run without preallocation, with sync
> > >     +ERROR: FIEMAP claimed there was data at a block which should be a hole, and FIBMAP confirmend that it is in fact a hole, so FIEMAP is wrong: 35
> > >     +ERROR: found an allocated extent where a hole should be: 35
> > >     +map is 'DHDDHHDDHDDHHHHDDDDDHHHHHHHDHDDDHHDHDHHHHHDDHDDHHDDHDHHDDDHHHHDDDDHDHHDDHHHDDDDHHDHDDDHHDHDDDHDHHHHHDHDHDHDHHDDHDHHHHDHHDDDDDDDH'
> > >     +logical: [      27..      27] phys:       67..      67 flags: 0x000 tot: 1
> > >     +logical: [      29..      31] phys:       69..      71 flags: 0x000 tot: 3
> > >     ...
> > >     (Run 'diff -u /home/dave/src/xfstests-dev/tests/generic/225.out /home/dave/src/xfstests-dev/results//xfs_align/generic/225.out.bad'  to see the entire diff)
> > > 
> > > I haven't looked into this yet, but nothing is reporting data
> > > corruptions so I suspect it's just the stripe aligned allocation
> > > leaving unwritten extents in places the test is expecting holes to
> > > exist...
> > 
> > That's the FIEMAP tester program not expecting that areas of the file
> > that it didn't write to can have unwritten extents mapped.  I'm testing
> > patches to fix all that tonight too.  If I can ever get these %#@%)#%!!!
> > orchestration scripts to work correctly.
> 
> OK.
> 
> FWIW, I've just found another bug in the stripe aligned allocation
> at EOF that is triggered by the filestreams code hitting ENOSPC
> conditions. xfs/170 seems to hit it fairly reliably - it's marking
> args->pag as NULL and not resetting the caller pag correctly and the
> high level filestreams failure code is expecting args->pag to be set
> because it owns the reference...
> 
> I hope to have a fix for that one on the list this afternoon....

Oh, yeah, I hit that one too.  I'll send out my fixes after the ext4
concall and we can sync up on that.

--D

> -Dave.
> -- 
> Dave Chinner
> david@fromorbit.com