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[PATCH 0/2 v2] Fix data corruption when blocksize < pagesize for mmapped

To: linux-fsdevel@xxxxxxxxxxxxxxx
Subject: [PATCH 0/2 v2] Fix data corruption when blocksize < pagesize for mmapped data
From: Jan Kara <jack@xxxxxxx>
Date: Fri, 10 Oct 2014 16:23:05 +0200
Cc: linux-ext4@xxxxxxxxxxxxxxx, Dave Chinner <david@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, cluster-devel@xxxxxxxxxx, Steven Whitehouse <swhiteho@xxxxxxxxxx>, Mark Fasheh <mfasheh@xxxxxxxx>, Joel Becker <jlbec@xxxxxxxxxxxx>, ocfs2-devel@xxxxxxxxxxxxxx, reiserfs-devel@xxxxxxxxxxxxxxx, Jeff Mahoney <jeffm@xxxxxxx>, Dave Kleikamp <shaggy@xxxxxxxxxx>, jfs-discussion@xxxxxxxxxxxxxxxxxxxxx, tytso@xxxxxxx, viro@xxxxxxxxxxxxxxxxxx, Jan Kara <jack@xxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx

  this is a second version of the patches to fix data corruption in mmapped
data when blocksize < pagesize as tested by xfstests generic/030 test.
The patchset fixes XFS and ext4. I've checked and btrfs doesn't need fixing
because it doesn't support blocksize < pagesize. If that's ever going
to change btrfs will likely need a similar treatment. ocfs2, ext2, ext3 are
OK since they happily allocate blocks during writeback. For other filesystems
like gfs2, ubifs, nilfs, ceph,... I'm not sure whether they support blocksize <
pagesize at all. Interesting is also NFS which may care but I don't understand
its ->page_mkwrite() handler good enough to judge.

Changes since v1:
- changed helper function name and moved it to mm/truncate.c - I originally
  thought we can make the helper function update i_size to simplify the
  interface but it's actually impossible due to generic_write_end() lock
  ordering constraints.
- used round_up() instead of ALIGN()
- taught truncate_setsize() to use the helper function


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