[Cluster-devel] [PATCH 0/2] fix gfs2 truncate race

[Benjamin Marzinski <bmarzins@redhat.com>]

If gfs2 tries to write out a page of a file with data journaling
enabled, while that file is being truncated, it can cause a kernel
panic. The problem is that the page it is writing out may point to past
the end of the file. If this happens, gfs2 will try to invalidate the
page.  However, it can't invalidate a journaled page with buffers in the
in-memory log, without revoking those buffers, so that there is no
chance of corruption if the machine crashes and later has its journal
replayed.  If the page is being written out by the log flush code, there
is no way that it can add a revoke entry onto the log during the flush.

To solve this, gfs2 simply writes out journalled data pages that point
past the end of the file, since the truncate is still in progress, and
everything will be cleaned up before the file is unlocked, or the blocks
are marked free. Doing this involves both a gfs2 change and exporting an
additional symbol from the vfs.

Benjamin Marzinski (2):
  fs: export __block_write_full_page
  gfs2: writeout truncated pages

 fs/buffer.c                 |  3 ++-
 fs/gfs2/aops.c              | 37 +++++++++++++++++++++++++++----------
 include/linux/buffer_head.h |  3 +++
 3 files changed, 32 insertions(+), 11 deletions(-)

-- 
1.8.3.1