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Subject[patch 57/60] ext4: Fix sub-block zeroing for writes into preallocated extents

-stable review patch. If anyone has any objections, please let us know.

------------------
From: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

(cherry picked from commit 9c1ee184a30394e54165fa4c15923cabd952c106)

We need to mark the buffer_head mapping preallocated space as new
during write_begin. Otherwise we don't zero out the page cache content
properly for a partial write. This will cause file corruption with
preallocation.

Now that we mark the buffer_head new we also need to have a valid
buffer_head blocknr so that unmap_underlying_metadata() unmaps the
correct block.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
fs/ext4/extents.c | 2 ++
fs/ext4/inode.c | 7 +++++++
2 files changed, 9 insertions(+)

--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -2670,6 +2670,8 @@ int ext4_ext_get_blocks(handle_t *handle
if (allocated > max_blocks)
allocated = max_blocks;
set_buffer_unwritten(bh_result);
+ bh_result->b_bdev = inode->i_sb->s_bdev;
+ bh_result->b_blocknr = newblock;
goto out2;
}

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2131,6 +2131,13 @@ static int ext4_da_get_block_prep(struct
set_buffer_delay(bh_result);
} else if (ret > 0) {
bh_result->b_size = (ret << inode->i_blkbits);
+ /*
+ * With sub-block writes into unwritten extents
+ * we also need to mark the buffer as new so that
+ * the unwritten parts of the buffer gets correctly zeroed.
+ */
+ if (buffer_unwritten(bh_result))
+ set_buffer_new(bh_result);
ret = 0;
}




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