Btrfs: fix uncompleted transaction

In some cases, we need commit the current transaction, but don't want
to start a new one if there is no running transaction, so we introduce
the function - btrfs_attach_transaction(), which can catch the current
transaction, and return -ENOENT if there is no running transaction.

But no running transaction doesn't mean the current transction completely,
because we removed the running transaction before it completes. In some
cases, it doesn't matter. But in some special cases, such as freeze fs, we
hope the transaction is fully on disk, it will introduce some bugs, for
example, we may feeze the fs and dump the data in the disk, if the transction
doesn't complete, we would dump inconsistent data. So we need fix the above
problem for those cases.

We fixes this problem by introducing a function:
	btrfs_attach_transaction_barrier()
if we hope all the transaction is fully on the disk, even they are not
running, we can use this function.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 0f68729f261e411cff3afeb3853b6c641372df44..e0893036da08ca1bc56f8113ab6ce25c75f55bbf 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3114,7 +3114,7 @@ static noinline long btrfs_ioctl_start_sync(struct btrfs_root *root,
        u64 transid;
        int ret;
 
-       trans = btrfs_attach_transaction(root);
+       trans = btrfs_attach_transaction_barrier(root);
        if (IS_ERR(trans)) {
                if (PTR_ERR(trans) != -ENOENT)
                        return PTR_ERR(trans);

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index e0ea1278377a5cbe340e2473a5270258a9b0f82a..db1ba9a2ed64b0336649449d4292012b5406bf68 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -878,7 +878,7 @@ int btrfs_sync_fs(struct super_block *sb, int wait)
 
        btrfs_wait_ordered_extents(root, 0);
 
-       trans = btrfs_attach_transaction(root);
+       trans = btrfs_attach_transaction_barrier(root);
        if (IS_ERR(trans)) {
                /* no transaction, don't bother */
                if (PTR_ERR(trans) == -ENOENT)
@@ -1563,7 +1563,7 @@ static int btrfs_freeze(struct super_block *sb)
        struct btrfs_trans_handle *trans;
        struct btrfs_root *root = btrfs_sb(sb)->tree_root;
 
-       trans = btrfs_attach_transaction(root);
+       trans = btrfs_attach_transaction_barrier(root);
        if (IS_ERR(trans)) {
                /* no transaction, don't bother */
                if (PTR_ERR(trans) == -ENOENT)

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 5767ea1c0150288c552aab2d99754dda8be9e8c7..c1ce664c0c39e47e7e39e9dac0d8dddeeab38822 100644 (file)
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -469,11 +469,43 @@ struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *root
        return start_transaction(root, 0, TRANS_USERSPACE, 0);
 }
 
+/*
+ * btrfs_attach_transaction() - catch the running transaction
+ *
+ * It is used when we want to commit the current the transaction, but
+ * don't want to start a new one.
+ *
+ * Note: If this function return -ENOENT, it just means there is no
+ * running transaction. But it is possible that the inactive transaction
+ * is still in the memory, not fully on disk. If you hope there is no
+ * inactive transaction in the fs when -ENOENT is returned, you should
+ * invoke
+ *     btrfs_attach_transaction_barrier()
+ */
 struct btrfs_trans_handle *btrfs_attach_transaction(struct btrfs_root *root)
 {
        return start_transaction(root, 0, TRANS_ATTACH, 0);
 }
 
+/*
+ * btrfs_attach_transaction() - catch the running transaction
+ *
+ * It is similar to the above function, the differentia is this one
+ * will wait for all the inactive transactions until they fully
+ * complete.
+ */
+struct btrfs_trans_handle *
+btrfs_attach_transaction_barrier(struct btrfs_root *root)
+{
+       struct btrfs_trans_handle *trans;
+
+       trans = start_transaction(root, 0, TRANS_ATTACH, 0);
+       if (IS_ERR(trans) && PTR_ERR(trans) == -ENOENT)
+               btrfs_wait_for_commit(root, 0);
+
+       return trans;
+}
+
 /* wait for a transaction commit to be fully complete */
 static noinline void wait_for_commit(struct btrfs_root *root,
                                    struct btrfs_transaction *commit)

diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 3f772fd0191ac1a4ef63c2b33660b4fc39dd4a0b..5afd7b1dceacf27a92e2b026aa7d76432ee9f18a 100644 (file)
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -112,6 +112,8 @@ struct btrfs_trans_handle *btrfs_start_transaction_lflush(
 struct btrfs_trans_handle *btrfs_join_transaction(struct btrfs_root *root);
 struct btrfs_trans_handle *btrfs_join_transaction_nolock(struct btrfs_root *root);
 struct btrfs_trans_handle *btrfs_attach_transaction(struct btrfs_root *root);
+struct btrfs_trans_handle *btrfs_attach_transaction_barrier(
+                                       struct btrfs_root *root);
 struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *root);
 int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid);
 int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,