4 files changed, 124 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 88c0fb7e12d..e5d66b13c17 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -901,6 +901,7 @@ struct btrfs_fs_info {
         struct btrfs_transaction *running_transaction;
         wait_queue_head_t transaction_throttle;
         wait_queue_head_t transaction_wait;
+        wait_queue_head_t transaction_blocked_wait;
         wait_queue_head_t async_submit_wait;
 
         struct btrfs_super_block super_copy;
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index e163424c7fc..b40dfe48017 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1679,6 +1679,7 @@ struct btrfs_root *open_ctree(struct super_block *sb,
 
         init_waitqueue_head(&fs_info->transaction_throttle);
         init_waitqueue_head(&fs_info->transaction_wait);
+        init_waitqueue_head(&fs_info->transaction_blocked_wait);
         init_waitqueue_head(&fs_info->async_submit_wait);
 
         __setup_root(4096, 4096, 4096, 4096, tree_root,
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 700dc4b34ad..9f40bfc9c45 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1007,6 +1007,123 @@ int btrfs_transaction_blocked(struct btrfs_fs_info *info)
         return ret;
 }
 
+/*
+ * wait for the current transaction commit to start and block subsequent
+ * transaction joins
+ */
+static void wait_current_trans_commit_start(struct btrfs_root *root,
+                                            struct btrfs_transaction *trans)
+{
+        DEFINE_WAIT(wait);
+
+        if (trans->in_commit)
+                return;
+
+        while (1) {
+                prepare_to_wait(&root->fs_info->transaction_blocked_wait, &wait,
+                                TASK_UNINTERRUPTIBLE);
+                if (trans->in_commit) {
+                        finish_wait(&root->fs_info->transaction_blocked_wait,
+                                    &wait);
+                        break;
+                }
+                mutex_unlock(&root->fs_info->trans_mutex);
+                schedule();
+                mutex_lock(&root->fs_info->trans_mutex);
+                finish_wait(&root->fs_info->transaction_blocked_wait, &wait);
+        }
+}
+
+/*
+ * wait for the current transaction to start and then become unblocked.
+ * caller holds ref.
+ */
+static void wait_current_trans_commit_start_and_unblock(struct btrfs_root *root,
+                                         struct btrfs_transaction *trans)
+{
+        DEFINE_WAIT(wait);
+
+        if (trans->commit_done || (trans->in_commit && !trans->blocked))
+                return;
+
+        while (1) {
+                prepare_to_wait(&root->fs_info->transaction_wait, &wait,
+                                TASK_UNINTERRUPTIBLE);
+                if (trans->commit_done ||
+                    (trans->in_commit && !trans->blocked)) {
+                        finish_wait(&root->fs_info->transaction_wait,
+                                    &wait);
+                        break;
+                }
+                mutex_unlock(&root->fs_info->trans_mutex);
+                schedule();
+                mutex_lock(&root->fs_info->trans_mutex);
+                finish_wait(&root->fs_info->transaction_wait,
+                            &wait);
+        }
+}
+
+/*
+ * commit transactions asynchronously. once btrfs_commit_transaction_async
+ * returns, any subsequent transaction will not be allowed to join.
+ */
+struct btrfs_async_commit {
+        struct btrfs_trans_handle *newtrans;
+        struct btrfs_root *root;
+        struct delayed_work work;
+};
+
+static void do_async_commit(struct work_struct *work)
+{
+        struct btrfs_async_commit *ac =
+                container_of(work, struct btrfs_async_commit, work.work);
+
+        btrfs_commit_transaction(ac->newtrans, ac->root);
+        kfree(ac);
+}
+
+int btrfs_commit_transaction_async(struct btrfs_trans_handle *trans,
+                                   struct btrfs_root *root,
+                                   int wait_for_unblock)
+{
+        struct btrfs_async_commit *ac;
+        struct btrfs_transaction *cur_trans;
+
+        ac = kmalloc(sizeof(*ac), GFP_NOFS);
+        BUG_ON(!ac);
+
+        INIT_DELAYED_WORK(&ac->work, do_async_commit);
+        ac->root = root;
+        ac->newtrans = btrfs_join_transaction(root, 0);
+
+        /* take transaction reference */
+        mutex_lock(&root->fs_info->trans_mutex);
+        cur_trans = trans->transaction;
+        cur_trans->use_count++;
+        mutex_unlock(&root->fs_info->trans_mutex);
+
+        btrfs_end_transaction(trans, root);
+        schedule_delayed_work(&ac->work, 0);
+
+        /* wait for transaction to start and unblock */
+        mutex_lock(&root->fs_info->trans_mutex);
+        if (wait_for_unblock)
+                wait_current_trans_commit_start_and_unblock(root, cur_trans);
+        else
+                wait_current_trans_commit_start(root, cur_trans);
+        put_transaction(cur_trans);
+        mutex_unlock(&root->fs_info->trans_mutex);
+
+        return 0;
+}
+
+/*
+ * btrfs_transaction state sequence:
+ *    in_commit = 0, blocked = 0  (initial)
+ *    in_commit = 1, blocked = 1
+ *    blocked = 0
+ *    commit_done = 1
+ */
 int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
                              struct btrfs_root *root)
 {
@@ -1057,6 +1174,8 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 
         trans->transaction->in_commit = 1;
         trans->transaction->blocked = 1;
+        wake_up(&root->fs_info->transaction_blocked_wait);
+
         if (cur_trans->list.prev != &root->fs_info->trans_list) {
                 prev_trans = list_entry(cur_trans->list.prev,
                                         struct btrfs_transaction, list);
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 15f83e1c1ef..e1908e6872f 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -108,6 +108,9 @@ int btrfs_defrag_root(struct btrfs_root *root, int cacheonly);
 int btrfs_clean_old_snapshots(struct btrfs_root *root);
 int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
                              struct btrfs_root *root);
+int btrfs_commit_transaction_async(struct btrfs_trans_handle *trans,
+                                   struct btrfs_root *root,
+                                   int wait_for_unblock);
 int btrfs_end_transaction_throttle(struct btrfs_trans_handle *trans,
                                    struct btrfs_root *root);
 int btrfs_should_end_transaction(struct btrfs_trans_handle *trans,