Btrfs: Don't allow written blocks from this transaction to be reallocated

When a block is freed, it can be immediately reused if it is from
the current transaction.  But, an extra check is required to make sure
the block had not been written yet.  If it were reused after being written,
the transid in the block header might match the transid of the
next time the block was allocated.

The parent node records the transaction ID of the block it is pointing to,
and this is used as part of validating the block on reads.  So, there
can only be one version of a block per transaction.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 1885ec4280c88cfbfd2e9babc600dccfe9c177aa..0c0dde6d96149288a6d6abb5ce1207fddc2cb882 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -1288,7 +1288,9 @@ static int pin_down_bytes(struct btrfs_root *root, u64 bytenr, u32 num_bytes,
                                    root->fs_info->running_transaction->transid;
                                u64 header_transid =
                                        btrfs_header_generation(buf);
-                               if (header_transid == transid) {
+                               if (header_transid == transid &&
+                                   !btrfs_header_flag(buf,
+                                              BTRFS_HEADER_FLAG_WRITTEN)) {
                                        clean_tree_block(NULL, root, buf);
                                        free_extent_buffer(buf);
                                        return 1;