[PATCH][BUG] jbd: fix the root cause of "no transactions" error in __log_wait_for_space()

@@ -96,7 +96,7 @@ static int __try_to_free_cp_buf(struct j
 	if (jh->b_jlist == BJ_None && !buffer_locked(bh) &&
 	    !buffer_dirty(bh) && !buffer_write_io_error(bh)) {
 		JBUFFER_TRACE(jh, "remove from checkpoint list");
-		ret = __journal_remove_checkpoint(jh) + 1;
+		ret = __journal_remove_checkpoint(jh, false) + 1;
 		jbd_unlock_bh_state(bh);
 		journal_remove_journal_head(bh);
 		BUFFER_TRACE(bh, "release");

@@ -221,7 +221,7 @@ restart:
 		 * Now in whatever state the buffer currently is, we know that
 		 * it has been written out and so we can drop it from the list
 		 */
-		released = __journal_remove_checkpoint(jh);
+		released = __journal_remove_checkpoint(jh, true);
 		jbd_unlock_bh_state(bh);
 		journal_remove_journal_head(bh);
 		__brelse(bh);

@@ -287,7 +287,7 @@ static int __process_buffer(journal_t *j
 			ret = -EIO;
 		J_ASSERT_JH(jh, !buffer_jbddirty(bh));
 		BUFFER_TRACE(bh, "remove from checkpoint");
-		__journal_remove_checkpoint(jh);
+		__journal_remove_checkpoint(jh, true);
 		spin_unlock(&journal->j_list_lock);
 		jbd_unlock_bh_state(bh);
 		journal_remove_journal_head(bh);

@@ -366,6 +366,16 @@ restart:
 		struct journal_head *jh;
 		int retry = 0, err;
 
+		/* 
+		 * Remove an oldest checkpoint transaction only if it has no
+		 * journal head.
+		 */
+		if (transaction->t_checkpoint_list == NULL
+		   && transaction->t_checkpoint_io_list == NULL) {
+			__journal_drop_transaction(journal, transaction);
+			wake_up(&journal->j_wait_logspace);
+			goto out;
+		}
 		while (!retry && transaction->t_checkpoint_list) {
 			struct buffer_head *bh;
 

@@ -614,12 +624,16 @@ out:
  *
  * The function returns 1 if it frees the transaction, 0 otherwise.
  *
+ * can_remove: 
+ *	false - we don't remove a checkpoint transaction.
+ *	true  - we remove a checkpoint transaction.
+ *
  * This function is called with the journal locked.
  * This function is called with j_list_lock held.
  * This function is called with jbd_lock_bh_state(jh2bh(jh))
  */
 
-int __journal_remove_checkpoint(struct journal_head *jh)
+int __journal_remove_checkpoint(struct journal_head *jh, bool can_remove)
 {
 	transaction_t *transaction;
 	journal_t *journal;

@@ -636,6 +650,9 @@ int __journal_remove_checkpoint(struct j
 	__buffer_unlink(jh);
 	jh->b_cp_transaction = NULL;
 
+	if (!can_remove)
+		goto out;
+
 	if (transaction->t_checkpoint_list != NULL ||
 	    transaction->t_checkpoint_io_list != NULL)
 		goto out;

@@ -833,7 +833,7 @@ restart_loop:
 		cp_transaction = jh->b_cp_transaction;
 		if (cp_transaction) {
 			JBUFFER_TRACE(jh, "remove from old cp transaction");
-			__journal_remove_checkpoint(jh);
+			__journal_remove_checkpoint(jh, false);
 		}
 
 		/* Only re-checkpoint the buffer_head if it is marked

@@ -1648,7 +1648,7 @@ __journal_try_to_free_buffer(journal_t *
 		/* written-back checkpointed metadata buffer */
 		if (jh->b_jlist == BJ_None) {
 			JBUFFER_TRACE(jh, "remove from checkpoint list");
-			__journal_remove_checkpoint(jh);
+			__journal_remove_checkpoint(jh, false);
 			journal_remove_journal_head(bh);
 			__brelse(bh);
 		}

@@ -844,7 +844,7 @@ extern void journal_commit_transaction(j
 
 /* Checkpoint list management */
 int __journal_clean_checkpoint_list(journal_t *journal);
-int __journal_remove_checkpoint(struct journal_head *);
+int __journal_remove_checkpoint(struct journal_head *, bool);
 void __journal_insert_checkpoint(struct journal_head *, transaction_t *);
 
 /* Buffer IO */