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ext4: correctly migrate a file with a hole at the beginning

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Currently ext4_ind_migrate() doesn't correctly handle a file which
contains a hole at the beginning of the file.  This caused the migration
to be done incorrectly, and then if there is a subsequent following
delayed allocation write to the "hole", this would reclaim the same data
blocks again and results in fs corruption.

  # assmuing 4k block size ext4, with delalloc enabled
  # skip the first block and write to the second block
  xfs_io -fc "pwrite 4k 4k" -c "fsync" /mnt/ext4/testfile

  # converting to indirect-mapped file, which would move the data blocks
  # to the beginning of the file, but extent status cache still marks
  # that region as a hole
  chattr -e /mnt/ext4/testfile

  # delayed allocation writes to the "hole", reclaim the same data block
  # again, results in i_blocks corruption
  xfs_io -c "pwrite 0 4k" /mnt/ext4/testfile
  umount /mnt/ext4
  e2fsck -nf /dev/sda6
  ...
  Inode 53, i_blocks is 16, should be 8.  Fix? no
  ...

Signed-off-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
This commit is contained in:
Eryu Guan 2015-07-04 00:03:44 -04:00 committed by Theodore Ts'o
parent d6f123a929
commit 8974fec7d7
1 changed files with 5 additions and 4 deletions
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9
fs/ext4/migrate.c
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@ -620,7 +620,7 @@ int ext4_ind_migrate(struct inode *inode)
struct ext4_inode_info *ei = EXT4_I(inode);
struct ext4_extent *ex;
unsigned int i, len;
ext4_lblk_t end;
ext4_lblk_t start, end;
ext4_fsblk_t blk;
handle_t *handle;
int ret;
@ -659,11 +659,12 @@ int ext4_ind_migrate(struct inode *inode)
goto errout;
}
if (eh->eh_entries == 0)
blk = len = 0;
blk = len = start = end = 0;
else {
len = le16_to_cpu(ex->ee_len);
blk = ext4_ext_pblock(ex);
end = le32_to_cpu(ex->ee_block) + len - 1;
start = le32_to_cpu(ex->ee_block);
end = start + len - 1;
if (end >= EXT4_NDIR_BLOCKS) {
ret = -EOPNOTSUPP;
goto errout;
@ -672,7 +673,7 @@ int ext4_ind_migrate(struct inode *inode)
ext4_clear_inode_flag(inode, EXT4_INODE_EXTENTS);
memset(ei->i_data, 0, sizeof(ei->i_data));
for (i=0; i < len; i++)
for (i = start; i <= end; i++)
ei->i_data[i] = cpu_to_le32(blk++);
ext4_mark_inode_dirty(handle, inode);
errout: