Re: [PATCH 2/7] generic/427: try to ensure there's some free space before we do the aio test

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

On Tue, Aug 12, 2025 at 10:15:55PM -0700, Christoph Hellwig wrote:
> On Tue, Aug 12, 2025 at 11:54:59AM -0700, Darrick J. Wong wrote:
> > On Wed, Jul 30, 2025 at 07:18:48AM -0700, Christoph Hellwig wrote:
> > > On Tue, Jul 29, 2025 at 01:08:46PM -0700, Darrick J. Wong wrote:
> > > > The pwrite failure comes from the aio-dio-eof-race.c program because the
> > > > filesystem ran out of space.  There are no speculative posteof
> > > > preallocations on a zoned filesystem, so let's skip this test on those
> > > > setups.
> > > 
> > > Did it run out of space because it is overwriting and we need a new
> > > allocation (I've not actually seen this fail in my zoned testing,
> > > that's why I'm asking)?  If so it really should be using the new
> > > _require_inplace_writes Filipe just sent to the list.
> > 
> > I took a deeper look into what's going on here, and I think the
> > intermittent ENOSPC failures are caused by:
> > 
> > 1. First we write to every byte in the 256M zoned rt device so that
> >    0x55 gets written to the disk.
> > 2. Then we delete the huge file we created.
> > 3. The zoned garbage collector doesn't run.
> > 4. aio-dio-eof-race starts up and initiates an aiodio at pos 0.
> > 5. xfs_file_dio_write_zoned calls xfs_zoned_write_space_reserve
> > 6. xfs_zoned_space_reserve tries to decrement 64k from XC_FREE_RTEXTENTS
> >    but gets ENOSPC.
> > 7. We didn't pass XFS_ZR_GREEDY, so we error out.
> > 
> > If I make the test sleep until I see zonegc do some work before starting
> > aio-dio-eof-race, the problem goes away.  I'm not sure what the proper
> > solution is, but maybe it's adding a wake_up to the gc process and
> > waiting for it?
> 
> Isn't the problem here that zonegc only even sees the freed block
> after inodegc did run?  i.e. after 2 the inode hasn't been truncated
> yet, and thus the blocks haven't been marked as free.

Yeah... for the other ENOSPC-on-write paths, we kick inodegc, so maybe
xfs_zoned_space_reserve (or its caller, more likely) ought to do that
too?

--D