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Subject[PATCH 3.16.y-ckt 178/180] ext4: fix ZERO_RANGE bug hidden by flag aliasing
Date
3.16.7-ckt11 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Theodore Ts'o <tytso@mit.edu>

commit 713e8dde3e71e92db2d8cc8459d236ce1fb576ce upstream.

We accidently aliased EXT4_EX_NOCACHE and EXT4_GET_CONVERT_UNWRITTEN
falgs, which apparently was hiding a bug that was unmasked when this
flag aliasing issue was addressed (see the subsequent commit). The
reproduction case was:

fsx -N 10000 -l 500000 -r 4096 -t 4096 -w 4096 -Z -R -W /vdb/junk

... which would cause fsx to report corruption in the data file.

The fix we have is a bit of an overkill, but I'd much rather be
conservative for now, and we can optimize ZERO_RANGE_FL handling
later. The fact that we need to zap the extent_status cache for the
inode is unfortunate, but correctness is far more important than
performance.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: Namjae Jeon <namjae.jeon@samsung.com>
Cc: Moritz Muehlenhoff <jmm@debian.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
fs/ext4/extents.c | 21 ++++++++++++++-------
1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 467661264ad0..2a4b4f3b1ae2 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4796,7 +4796,8 @@ static long ext4_zero_range(struct file *file, loff_t offset,
max_blocks -= lblk;

flags = EXT4_GET_BLOCKS_CREATE_UNWRIT_EXT |
- EXT4_GET_BLOCKS_CONVERT_UNWRITTEN;
+ EXT4_GET_BLOCKS_CONVERT_UNWRITTEN |
+ EXT4_EX_NOCACHE;
if (mode & FALLOC_FL_KEEP_SIZE)
flags |= EXT4_GET_BLOCKS_KEEP_SIZE;

@@ -4834,15 +4835,21 @@ static long ext4_zero_range(struct file *file, loff_t offset,
ext4_inode_block_unlocked_dio(inode);
inode_dio_wait(inode);

+ ret = ext4_alloc_file_blocks(file, lblk, max_blocks, new_size,
+ flags, mode);
+ if (ret)
+ goto out_dio;
/*
* Remove entire range from the extent status tree.
+ *
+ * ext4_es_remove_extent(inode, lblk, max_blocks) is
+ * NOT sufficient. I'm not sure why this is the case,
+ * but let's be conservative and remove the extent
+ * status tree for the entire inode. There should be
+ * no outstanding delalloc extents thanks to the
+ * filemap_write_and_wait_range() call above.
*/
- ret = ext4_es_remove_extent(inode, lblk, max_blocks);
- if (ret)
- goto out_dio;
-
- ret = ext4_alloc_file_blocks(file, lblk, max_blocks, new_size,
- flags, mode);
+ ret = ext4_es_remove_extent(inode, 0, EXT_MAX_BLOCKS);
if (ret)
goto out_dio;
}

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