Btrfs: fix the deadlock between the transaction start/attach and commit (178260b2) · Commits · e / devices / android_kernel_fairphone_FP3

Now btrfs_commit_transaction() does this ret = btrfs_run_ordered_operations(root, 0) which async flushes all inodes on the ordered operations list, it introduced a deadlock that transaction-start task, transaction-commit task and the flush workers waited for each other. (See the following URL to get the detail http://marc.info/?l=linux-btrfs&m=136070705732646&w=2 ) As we know, if ->in_commit is set, it means someone is committing the current transaction, we should not try to join it if we are not JOIN or JOIN_NOLOCK, wait is the best choice for it. In this way, we can avoid the above problem. In this way, there is another benefit: there is no new transaction handle to block the transaction which is on the way of commit, once we set ->in_commit. Signed-off-by:

Miao Xie <miaox@cn.fujitsu.com> Signed-off-by:

Josef Bacik <jbacik@fusionio.com>

fs/btrfs/transaction.c

+16 −1

Original line number	Diff line number	Diff line
		@@ -50,6 +50,14 @@ static noinline void switch_commit_root(struct btrfs_root *root)
		root->commit_root = btrfs_root_node(root);
		}

		static inline int can_join_transaction(struct btrfs_transaction *trans,
		int type)
		{
		return !(trans->in_commit &&
		type != TRANS_JOIN &&
		type != TRANS_JOIN_NOLOCK);
		}

		/*
		* either allocate a new transaction or hop into the existing one
		*/
		@@ -85,6 +93,10 @@ static noinline int join_transaction(struct btrfs_root *root, int type)
		spin_unlock(&fs_info->trans_lock);
		return cur_trans->aborted;
		}
		if (!can_join_transaction(cur_trans, type)) {
		spin_unlock(&fs_info->trans_lock);
		return -EBUSY;
		}
		atomic_inc(&cur_trans->use_count);
		atomic_inc(&cur_trans->num_writers);
		cur_trans->num_joined++;
		@@ -360,8 +372,11 @@ start_transaction(struct btrfs_root *root, u64 num_items, int type,

		do {
		ret = join_transaction(root, type);
		if (ret == -EBUSY)
		if (ret == -EBUSY) {
		wait_current_trans(root);
		if (unlikely(type == TRANS_ATTACH))
		ret = -ENOENT;
		}
		} while (ret == -EBUSY);

		if (ret < 0) {