Re: [PATCH v7 04/12] ltp/fsx.c: Add atomic writes support to fsx

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

On Thu, Oct 23, 2025 at 04:44:36PM +0100, John Garry wrote:
> On 22/10/2025 08:40, Ojaswin Mujoo wrote:
> > > FWIW I see a somewhat different failure -- not data corruption, but
> > > pwrite returning failure:
> > > --- /run/fstests/bin/tests/generic/521.out      2025-07-15 14:45:15.100315255 -0700
> > > +++ /var/tmp/fstests/generic/521.out.bad        2025-10-21 10:33:39.032263811 -0700
> > > @@ -1,2 +1,668 @@
> > >   QA output created by 521
> > > +dowrite: write: Input/output error
> > Hmm that's strange. Can you try running the above command with
> > prep.fsxops that I've shared. You'll need to pull the fsx atomic write
> > changes in this patch for it to work. I've been running on non atomic
> > write device btw.
> 
> JFYI, I can see this issue with v6.18-rc2 and generic/760
> 
> I'll investigate...

I figured out why I'm seeing EIO from the ftrace output.  Apparently
xfs_atomic_write_cow_iomap_begin isn't detecting delalloc extents in the
cow fork and converting them to unwritten:

fsx-35984 [003]  1996.389571: xfs_file_direct_write: dev 8:0 ino 0x127 disize 0x88000 pos 0x20000 bytecount 0x10000
fsx-35984 [003]  1996.389572: iomap_dio_rw_begin:   dev 8:0 ino 0x127 size 0x88000 offset 0x20000 length 0x10000 done_before 0x0 flags ATOMIC|DIRECT dio_flags  aio 0
fsx-35984 [003]  1996.389583: iomap_iter:           dev 8:0 ino 0x127 pos 0x20000 length 0x10000 status 0 flags WRITE|DIRECT|ATOMIC (0x211) ops xfs_atomic_write_cow_iomap_ops caller __iomap_dio_rw+0x1cb
fsx-35984 [003]  1996.389583: xfs_iomap_atomic_write_cow: dev 8:0 ino 0x127 pos 0x20000 bytecount 0x10000
fsx-35984 [003]  1996.389584: xfs_iomap_found:      dev 8:0 ino 0x127 disize 0x88000 pos 0x20000 bytecount 0x10000 fork cow startoff 0x20 startblock 0xffffffffe0007 fsbcount 0x10
fsx-35984 [003]  1996.389584: iomap_iter_dstmap:    dev 8:0 ino 0x127 bdev 8:0 addr 0xffffffffffffffff offset 0x20000 length 0x10000 type DELALLOC (0x1) flags DIRTY|SHARED (0x6)
fsx-35984 [003]  1996.389595: console:              Direct I/O collision with buffered writes! File: /junk Comm: fsx
fsx-35984 [003]  1996.391183: iomap_iter:           dev 8:0 ino 0x127 pos 0x20000 length 0x10000 status -5 flags WRITE|DIRECT|ATOMIC (0x211) ops xfs_atomic_write_cow_iomap_ops caller __iomap_dio_rw+0x1cb
fsx-35984 [003]  1996.391184: iomap_dio_complete:   dev 8:0 ino 0x127 size 0x88000 offset 0x20000 flags ATOMIC|DIRECT aio 0 error -5 ret -5

I suspect this needs a xfs_bmapi_convert_delalloc call somewhere around
the end of that function.

--D