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authorFilipe Manana <fdmanana@suse.com>2015-06-25 04:17:46 +0100
committerChris Mason <clm@fb.com>2015-07-01 17:17:12 -0700
commita89ca6f24ffe435edad57de02eaabd37a2c6bff6 (patch)
tree9428cf5260c00f66637d29f3d8c37902c6127ddb /fs/btrfs/tree-log.c
parent36283bf777d963fac099213297e155d071096994 (diff)
Btrfs: fix fsync after truncate when no_holes feature is enabled
When we have the no_holes feature enabled, if a we truncate a file to a smaller size, truncate it again but to a size greater than or equals to its original size and fsync it, the log tree will not have any information about the hole covering the range [truncate_1_offset, new_file_size[. Which means if the fsync log is replayed, the file will remain with the state it had before both truncate operations. Without the no_holes feature this does not happen, since when the inode is logged (full sync flag is set) it will find in the fs/subvol tree a leaf with a generation matching the current transaction id that has an explicit extent item representing the hole. Fix this by adding an explicit extent item representing a hole between the last extent and the inode's i_size if we are doing a full sync. The issue is easy to reproduce with the following test case for fstests: . ./common/rc . ./common/filter . ./common/dmflakey _need_to_be_root _supported_fs generic _supported_os Linux _require_scratch _require_dm_flakey # This test was motivated by an issue found in btrfs when the btrfs # no-holes feature is enabled (introduced in kernel 3.14). So enable # the feature if the fs being tested is btrfs. if [ $FSTYP == "btrfs" ]; then _require_btrfs_fs_feature "no_holes" _require_btrfs_mkfs_feature "no-holes" MKFS_OPTIONS="$MKFS_OPTIONS -O no-holes" fi rm -f $seqres.full _scratch_mkfs >>$seqres.full 2>&1 _init_flakey _mount_flakey # Create our test files and make sure everything is durably persisted. $XFS_IO_PROG -f -c "pwrite -S 0xaa 0 64K" \ -c "pwrite -S 0xbb 64K 61K" \ $SCRATCH_MNT/foo | _filter_xfs_io $XFS_IO_PROG -f -c "pwrite -S 0xee 0 64K" \ -c "pwrite -S 0xff 64K 61K" \ $SCRATCH_MNT/bar | _filter_xfs_io sync # Now truncate our file foo to a smaller size (64Kb) and then truncate # it to the size it had before the shrinking truncate (125Kb). Then # fsync our file. If a power failure happens after the fsync, we expect # our file to have a size of 125Kb, with the first 64Kb of data having # the value 0xaa and the second 61Kb of data having the value 0x00. $XFS_IO_PROG -c "truncate 64K" \ -c "truncate 125K" \ -c "fsync" \ $SCRATCH_MNT/foo # Do something similar to our file bar, but the first truncation sets # the file size to 0 and the second truncation expands the size to the # double of what it was initially. $XFS_IO_PROG -c "truncate 0" \ -c "truncate 253K" \ -c "fsync" \ $SCRATCH_MNT/bar _load_flakey_table $FLAKEY_DROP_WRITES _unmount_flakey # Allow writes again, mount to trigger log replay and validate file # contents. _load_flakey_table $FLAKEY_ALLOW_WRITES _mount_flakey # We expect foo to have a size of 125Kb, the first 64Kb of data all # having the value 0xaa and the remaining 61Kb to be a hole (all bytes # with value 0x00). echo "File foo content after log replay:" od -t x1 $SCRATCH_MNT/foo # We expect bar to have a size of 253Kb and no extents (any byte read # from bar has the value 0x00). echo "File bar content after log replay:" od -t x1 $SCRATCH_MNT/bar status=0 exit The expected file contents in the golden output are: File foo content after log replay: 0000000 aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa * 0200000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 * 0372000 File bar content after log replay: 0000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 * 0772000 Without this fix, their contents are: File foo content after log replay: 0000000 aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa * 0200000 bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb * 0372000 File bar content after log replay: 0000000 ee ee ee ee ee ee ee ee ee ee ee ee ee ee ee ee * 0200000 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff * 0372000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 * 0772000 A test case submission for fstests follows soon. Signed-off-by: Filipe Manana <fdmanana@suse.com> Reviewed-by: Liu Bo <bo.li.liu@oracle.com> Signed-off-by: Chris Mason <clm@fb.com>
Diffstat (limited to 'fs/btrfs/tree-log.c')
-rw-r--r--fs/btrfs/tree-log.c108
1 files changed, 108 insertions, 0 deletions
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 66f87156882f..9c45431e69ab 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -4197,6 +4197,107 @@ static int btrfs_log_all_xattrs(struct btrfs_trans_handle *trans,
return 0;
}
+/*
+ * If the no holes feature is enabled we need to make sure any hole between the
+ * last extent and the i_size of our inode is explicitly marked in the log. This
+ * is to make sure that doing something like:
+ *
+ * 1) create file with 128Kb of data
+ * 2) truncate file to 64Kb
+ * 3) truncate file to 256Kb
+ * 4) fsync file
+ * 5) <crash/power failure>
+ * 6) mount fs and trigger log replay
+ *
+ * Will give us a file with a size of 256Kb, the first 64Kb of data match what
+ * the file had in its first 64Kb of data at step 1 and the last 192Kb of the
+ * file correspond to a hole. The presence of explicit holes in a log tree is
+ * what guarantees that log replay will remove/adjust file extent items in the
+ * fs/subvol tree.
+ *
+ * Here we do not need to care about holes between extents, that is already done
+ * by copy_items(). We also only need to do this in the full sync path, where we
+ * lookup for extents from the fs/subvol tree only. In the fast path case, we
+ * lookup the list of modified extent maps and if any represents a hole, we
+ * insert a corresponding extent representing a hole in the log tree.
+ */
+static int btrfs_log_trailing_hole(struct btrfs_trans_handle *trans,
+ struct btrfs_root *root,
+ struct inode *inode,
+ struct btrfs_path *path)
+{
+ int ret;
+ struct btrfs_key key;
+ u64 hole_start;
+ u64 hole_size;
+ struct extent_buffer *leaf;
+ struct btrfs_root *log = root->log_root;
+ const u64 ino = btrfs_ino(inode);
+ const u64 i_size = i_size_read(inode);
+
+ if (!btrfs_fs_incompat(root->fs_info, NO_HOLES))
+ return 0;
+
+ key.objectid = ino;
+ key.type = BTRFS_EXTENT_DATA_KEY;
+ key.offset = (u64)-1;
+
+ ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+ ASSERT(ret != 0);
+ if (ret < 0)
+ return ret;
+
+ ASSERT(path->slots[0] > 0);
+ path->slots[0]--;
+ leaf = path->nodes[0];
+ btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
+
+ if (key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY) {
+ /* inode does not have any extents */
+ hole_start = 0;
+ hole_size = i_size;
+ } else {
+ struct btrfs_file_extent_item *extent;
+ u64 len;
+
+ /*
+ * If there's an extent beyond i_size, an explicit hole was
+ * already inserted by copy_items().
+ */
+ if (key.offset >= i_size)
+ return 0;
+
+ extent = btrfs_item_ptr(leaf, path->slots[0],
+ struct btrfs_file_extent_item);
+
+ if (btrfs_file_extent_type(leaf, extent) ==
+ BTRFS_FILE_EXTENT_INLINE) {
+ len = btrfs_file_extent_inline_len(leaf,
+ path->slots[0],
+ extent);
+ ASSERT(len == i_size);
+ return 0;
+ }
+
+ len = btrfs_file_extent_num_bytes(leaf, extent);
+ /* Last extent goes beyond i_size, no need to log a hole. */
+ if (key.offset + len > i_size)
+ return 0;
+ hole_start = key.offset + len;
+ hole_size = i_size - hole_start;
+ }
+ btrfs_release_path(path);
+
+ /* Last extent ends at i_size. */
+ if (hole_size == 0)
+ return 0;
+
+ hole_size = ALIGN(hole_size, root->sectorsize);
+ ret = btrfs_insert_file_extent(trans, log, ino, hole_start, 0, 0,
+ hole_size, 0, hole_size, 0, 0, 0);
+ return ret;
+}
+
/* log a single inode in the tree log.
* At least one parent directory for this inode must exist in the tree
* or be logged already.
@@ -4460,6 +4561,13 @@ next_slot:
err = btrfs_log_all_xattrs(trans, root, inode, path, dst_path);
if (err)
goto out_unlock;
+ if (max_key.type >= BTRFS_EXTENT_DATA_KEY && !fast_search) {
+ btrfs_release_path(path);
+ btrfs_release_path(dst_path);
+ err = btrfs_log_trailing_hole(trans, root, inode, path);
+ if (err)
+ goto out_unlock;
+ }
log_extents:
btrfs_release_path(path);
btrfs_release_path(dst_path);