ext4: Fix sub-block zeroing for writes into preallocated extents

(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>

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index acb98c9db48be1b47029c894012048411ddb0709..067cbc01b44502a28c35e12f1cccbdacc0b10b14 100644 (file)
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -2670,6 +2670,8 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
                                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;
                        }
 

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ee7790fce381e0bdd1bf10fe55135a9068f11d2a..301ed5b0fbf689ddba30923c78e7bce40b8ecdfb 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2131,6 +2131,13 @@ static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
                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;
        }