Btrfs: Tree logging fixes

* Pin down data blocks to prevent them from being reallocated like so:

trans 1: allocate file extent
trans 2: free file extent
trans 3: free file extent during old snapshot deletion
trans 3: allocate file extent to new file
trans 3: fsync new file

Before the tree logging code, this was legal because the fsync
would commit the transation that did the final data extent free
and the transaction that allocated the extent to the new file
at the same time.

With the tree logging code, the tree log subtransaction can commit
before the transaction that freed the extent.  If we crash,
we're left with two different files using the extent.

* Don't wait in start_transaction if log replay is going on.  This
avoids deadlocks from iput while we're cleaning up link counts in the
replay code.

* Don't deadlock in replay_one_name by trying to read an inode off
the disk while holding paths for the directory

* Hold the buffer lock while we mark a buffer as written.  This
closes a race where someone is changing a buffer while we write it.
They are supposed to mark it dirty again after they change it, but
this violates the cow rules.

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

1 files changed, 9 insertions, 4 deletions

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index d1ce8314b948..13d7ee8e0c52 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -1176,8 +1176,8 @@ static noinline int replay_one_name(struct btrfs_trans_handle *trans,
 	struct btrfs_key found_key;
 	struct btrfs_key log_key;
 	struct inode *dir;
-	struct inode *inode;
 	u8 log_type;
+	int exists;
 	int ret;
 
 	dir = read_one_inode(root, key->objectid);
@@ -1190,6 +1190,13 @@ static noinline int replay_one_name(struct btrfs_trans_handle *trans,
 		   name_len);
 
 	btrfs_dir_item_key_to_cpu(eb, di, &log_key);
+	exists = btrfs_lookup_inode(trans, root, path, &log_key, 0);
+	if (exists == 0)
+		exists = 1;
+	else
+		exists = 0;
+	btrfs_release_path(root, path);
+
 	if (key->type == BTRFS_DIR_ITEM_KEY) {
 		dst_di = btrfs_lookup_dir_item(trans, root, path, key->objectid,
 				       name, name_len, 1);
@@ -1224,11 +1231,9 @@ static noinline int replay_one_name(struct btrfs_trans_handle *trans,
 	 * don't drop the conflicting directory entry if the inode
 	 * for the new entry doesn't exist
 	 */
-	inode = read_one_inode(root, log_key.objectid);
-	if (!inode)
+	if (!exists)
 		goto out;
 
-	iput(inode);
 	ret = drop_one_dir_item(trans, root, path, dir, dst_di);
 	BUG_ON(ret);