[PATCH V2] Btrfs: fix deadlock when the process of delayed refs fails

[Miao Xie <miaox@cn.fujitsu.com>]

Delayed ref mutexes are taken inside btrfs_commit_transaction. A later call
fails and jumps to the cleanup_transaction label with these mutexes still held
causing deadlock when they are reacquired.

Fix this problem by unlocking those mutexes at the suitable place.

Reported-by: Daniel J Blueman <daniel@quora.org>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
---
Changelog from v1 -> v2:
- split the code of the run_one_delayed_ref()'s error path from the normal path
---
 fs/btrfs/delayed-ref.c |  8 ++++++++
 fs/btrfs/delayed-ref.h |  6 ++++++
 fs/btrfs/extent-tree.c | 36 ++++++++++++++++++++++++------------
 3 files changed, 38 insertions(+), 12 deletions(-)

diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
index ae94117..364cb90 100644
--- a/fs/btrfs/delayed-ref.c
+++ b/fs/btrfs/delayed-ref.c
@@ -422,6 +422,14 @@ again:
 	return 1;
 }
 
+void btrfs_release_ref_cluster(struct list_head *cluster)
+{
+	struct list_head *pos, *q;
+
+	list_for_each_safe(pos, q, cluster)
+		list_del_init(pos);
+}
+
 /*
  * helper function to update an extent delayed ref in the
  * rbtree.  existing and update must both have the same
diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h
index ab53005..fcc5a29 100644
--- a/fs/btrfs/delayed-ref.h
+++ b/fs/btrfs/delayed-ref.h
@@ -176,8 +176,14 @@ struct btrfs_delayed_ref_head *
 btrfs_find_delayed_ref_head(struct btrfs_trans_handle *trans, u64 bytenr);
 int btrfs_delayed_ref_lock(struct btrfs_trans_handle *trans,
 			   struct btrfs_delayed_ref_head *head);
+static inline void btrfs_delayed_ref_unlock(struct btrfs_delayed_ref_head *head)
+{
+	mutex_unlock(&head->mutex);
+}
+
 int btrfs_find_ref_cluster(struct btrfs_trans_handle *trans,
 			   struct list_head *cluster, u64 search_start);
+void btrfs_release_ref_cluster(struct list_head *cluster);
 
 int btrfs_check_delayed_seq(struct btrfs_fs_info *fs_info,
 			    struct btrfs_delayed_ref_root *delayed_refs,
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 3d3e2c1..93faf5e 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2160,7 +2160,6 @@ static int run_one_delayed_ref(struct btrfs_trans_handle *trans,
 						      node->num_bytes);
 			}
 		}
-		mutex_unlock(&head->mutex);
 		return ret;
 	}
 
@@ -2275,7 +2274,7 @@ static noinline int run_clustered_refs(struct btrfs_trans_handle *trans,
 			 * process of being added. Don't run this ref yet.
 			 */
 			list_del_init(&locked_ref->cluster);
-			mutex_unlock(&locked_ref->mutex);
+			btrfs_delayed_ref_unlock(locked_ref);
 			locked_ref = NULL;
 			delayed_refs->num_heads_ready++;
 			spin_unlock(&delayed_refs->lock);
@@ -2314,16 +2313,17 @@ static noinline int run_clustered_refs(struct btrfs_trans_handle *trans,
 				kfree(extent_op);
 
 				if (ret) {
-					printk(KERN_DEBUG "btrfs: run_delayed_extent_op returned %d\n", ret);
+					printk(KERN_DEBUG
+					       "btrfs: run_delayed_extent_op "
+					       "returned %d\n",
+					       ret);
 					spin_lock(&delayed_refs->lock);
+					btrfs_delayed_ref_unlock(locked_ref);
 					return ret;
 				}
 
 				goto next;
 			}
-
-			list_del_init(&locked_ref->cluster);
-			locked_ref = NULL;
 		}
 
 		ref->in_tree = 0;
@@ -2350,17 +2350,28 @@ static noinline int run_clustered_refs(struct btrfs_trans_handle *trans,
 
 		ret = run_one_delayed_ref(trans, root, ref, extent_op,
 					  must_insert_reserved);
-
-		btrfs_put_delayed_ref(ref);
 		kfree(extent_op);
-		count++;
-
 		if (ret) {
-			printk(KERN_DEBUG "btrfs: run_one_delayed_ref returned %d\n", ret);
+			btrfs_delayed_ref_unlock(locked_ref);
+			btrfs_put_delayed_ref(ref);
+			printk(KERN_DEBUG
+			       "btrfs: run_one_delayed_ref returned %d\n", ret);
 			spin_lock(&delayed_refs->lock);
 			return ret;
 		}
-
+		/*
+		 * If this node is a head, that means all the refs in this head
+		 * have been dealt with, and we will pick the next head to deal
+		 * with, so we must unlock the head and drop it from the cluster
+		 * list before we release it.
+		 */
+		if (btrfs_delayed_ref_is_head(ref)) {
+			list_del_init(&locked_ref->cluster);
+			btrfs_delayed_ref_unlock(locked_ref);
+			locked_ref = NULL;
+		}
+		btrfs_put_delayed_ref(ref);
+		count++;
 next:
 		cond_resched();
 		spin_lock(&delayed_refs->lock);
@@ -2510,6 +2521,7 @@ again:
 
 		ret = run_clustered_refs(trans, root, &cluster);
 		if (ret < 0) {
+			btrfs_release_ref_cluster(&cluster);
 			spin_unlock(&delayed_refs->lock);
 			btrfs_abort_transaction(trans, root, ret);
 			return ret;
-- 
1.7.11.7