[v2,0/2] nfs: two writeback error reporting fixes

Message

Scott Mayhew Aug. 1, 2020, 11:10 a.m. UTC

These fixes fix two regressions reported by Red Hat QE.  This first
issue reported was that writing a file larger than the available space
would result in a client hang instead of returning -ENOSPC.  The second
issue reported was that the client was returning -EIO instead of -EDQUOT
when a quota is exceeded.

On further investigation, I found that in the first issue the client
wasn't really hung.  Instead it was performing all of the requested
writes before it would eventually return -ENOSPC.  The dd command was
writing 400TB, which would have taken a few weeks to complete.
Adjusting the 'bs' and 'count' arguments so that the resulting file
would be much smaller (but still enough to fill up the space on the NFS
server) showed that the dd command would indeed complete with -ENOSPC.
But on older kernels even the 400TB dd would return -ENOSPC quickly.

In the second issue, I found that adding 'conv=fsync' would make the dd
command return -EDQUOT.  So what was happening with the original
command was that it was doing a close() without first calling fsync()
and the close() was returning -EIO.

I bisected both of these down to commit aded8d7b54f2 ("NFS: Don't
inadvertently clear writeback errors").  HOWEVER, as a test I reverted
that commit and it wasn't sufficient to bring back the old behavior.  I
turns out that was due to commit 6fbda89b257f ("NFS: Replace custom
error reporting mechanism with generic one").  This is why I listed the
second commit in the 'Fixes:' tag of both of my patches.

The first patch fixes the -EDQUOT issue and the second one fixes the
-ENOSPC issue.

-Scott

v2:
- Use filemap_sample_wb_err() & filemap_check_wb_err() instead of
  file_check_and_advance_wb_err() so that the error is not consumed.

Scott Mayhew (2):
  nfs: ensure correct writeback errors are returned on close()
  nfs: nfs_file_write() should check for writeback errors

 fs/nfs/file.c     | 17 +++++++++++++----
 fs/nfs/nfs4file.c |  5 ++++-
 2 files changed, 17 insertions(+), 5 deletions(-)