4 files changed, 49 insertions, 23 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 2c18a4eb4d5a..dcaf55695e6f 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1657,9 +1657,10 @@ static int transaction_kthread(void *arg)
                 spin_unlock(&root->fs_info->trans_lock);
 
                 /* If the file system is aborted, this will always fail. */
-                trans = btrfs_join_transaction(root);
+                trans = btrfs_attach_transaction(root);
                 if (IS_ERR(trans)) {
-                        cannot_commit = true;
+                        if (PTR_ERR(trans) != -ENOENT)
+                                cannot_commit = true;
                         goto sleep;
                 }
                 if (transid == trans->transid) {
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index fb260bbf59c6..f8b803f30ed8 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -854,10 +854,10 @@ int btrfs_sync_fs(struct super_block *sb, int wait)
 
         btrfs_wait_ordered_extents(root, 0);
 
-        trans = btrfs_join_transaction_freeze(root);
+        trans = btrfs_attach_transaction(root);
         if (IS_ERR(trans)) {
-                /* Frozen, don't bother */
-                if (PTR_ERR(trans) == -EPERM)
+                /* no transaction, don't bother */
+                if (PTR_ERR(trans) == -ENOENT)
                         return 0;
                 return PTR_ERR(trans);
         }
@@ -1511,7 +1511,17 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
 
 static int btrfs_freeze(struct super_block *sb)
 {
-        return 0;
+        struct btrfs_trans_handle *trans;
+        struct btrfs_root *root = btrfs_sb(sb)->tree_root;
+
+        trans = btrfs_attach_transaction(root);
+        if (IS_ERR(trans)) {
+                /* no transaction, don't bother */
+                if (PTR_ERR(trans) == -ENOENT)
+                        return 0;
+                return PTR_ERR(trans);
+        }
+        return btrfs_commit_transaction(trans, root);
 }
 
 static int btrfs_unfreeze(struct super_block *sb)
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index d0a2b7e49381..69139a356f71 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -53,7 +53,7 @@ static noinline void switch_commit_root(struct btrfs_root *root)
 /*
  * either allocate a new transaction or hop into the existing one
  */
-static noinline int join_transaction(struct btrfs_root *root, int nofail)
+static noinline int join_transaction(struct btrfs_root *root, int type)
 {
         struct btrfs_transaction *cur_trans;
         struct btrfs_fs_info *fs_info = root->fs_info;
@@ -67,7 +67,13 @@ loop:
         }
 
         if (fs_info->trans_no_join) {
-                if (!nofail) {
+                /* 
+                 * If we are JOIN_NOLOCK we're already committing a current
+                 * transaction, we just need a handle to deal with something
+                 * when committing the transaction, such as inode cache and
+                 * space cache. It is a special case.
+                 */
+                if (type != TRANS_JOIN_NOLOCK) {
                         spin_unlock(&fs_info->trans_lock);
                         return -EBUSY;
                 }
@@ -87,6 +93,13 @@ loop:
         }
         spin_unlock(&fs_info->trans_lock);
 
+        /*
+         * If we are ATTACH, we just want to catch the current transaction,
+         * and commit it. If there is no transaction, just return ENOENT.
+         */
+        if (type == TRANS_ATTACH)
+                return -ENOENT;
+
         cur_trans = kmem_cache_alloc(btrfs_transaction_cachep, GFP_NOFS);
         if (!cur_trans)
                 return -ENOMEM;
@@ -340,27 +353,28 @@ again:
          * because we're already holding a ref.  We need this because we could
          * have raced in and did an fsync() on a file which can kick a commit
          * and then we deadlock with somebody doing a freeze.
+         *
+         * If we are ATTACH, it means we just want to catch the current
+         * transaction and commit it, so we needn't do sb_start_intwrite(). 
          */
-        if (type != TRANS_JOIN_NOLOCK &&
-            !__sb_start_write(root->fs_info->sb, SB_FREEZE_FS, false)) {
-                if (type == TRANS_JOIN_FREEZE) {
-                        kmem_cache_free(btrfs_trans_handle_cachep, h);
-                        return ERR_PTR(-EPERM);
-                }
+        if (type < TRANS_JOIN_NOLOCK)
                 sb_start_intwrite(root->fs_info->sb);
-        }
 
         if (may_wait_transaction(root, type))
                 wait_current_trans(root);
 
         do {
-                ret = join_transaction(root, type == TRANS_JOIN_NOLOCK);
+                ret = join_transaction(root, type);
                 if (ret == -EBUSY)
                         wait_current_trans(root);
         } while (ret == -EBUSY);
 
         if (ret < 0) {
-                sb_end_intwrite(root->fs_info->sb);
+                /* We must get the transaction if we are JOIN_NOLOCK. */
+                BUG_ON(type == TRANS_JOIN_NOLOCK);
+
+                if (type < TRANS_JOIN_NOLOCK)
+                        sb_end_intwrite(root->fs_info->sb);
                 kmem_cache_free(btrfs_trans_handle_cachep, h);
                 return ERR_PTR(ret);
         }
@@ -432,9 +446,9 @@ struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *root
         return start_transaction(root, 0, TRANS_USERSPACE, 0);
 }
 
-struct btrfs_trans_handle *btrfs_join_transaction_freeze(struct btrfs_root *root)
+struct btrfs_trans_handle *btrfs_attach_transaction(struct btrfs_root *root)
 {
-        return start_transaction(root, 0, TRANS_JOIN_FREEZE, 0);
+        return start_transaction(root, 0, TRANS_ATTACH, 0);
 }
 
 /* wait for a transaction commit to be fully complete */
@@ -605,7 +619,7 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
                 }
         }
 
-        if (lock)
+        if (trans->type < TRANS_JOIN_NOLOCK)
                 sb_end_intwrite(root->fs_info->sb);
 
         WARN_ON(cur_trans != info->running_transaction);
@@ -1678,7 +1692,8 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
         put_transaction(cur_trans);
         put_transaction(cur_trans);
 
-        sb_end_intwrite(root->fs_info->sb);
+        if (trans->type < TRANS_JOIN_NOLOCK)
+                sb_end_intwrite(root->fs_info->sb);
 
         trace_btrfs_transaction_commit(root);
 
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 0630bd19396a..80961947a6b2 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -52,7 +52,7 @@ enum btrfs_trans_type {
         TRANS_JOIN,
         TRANS_USERSPACE,
         TRANS_JOIN_NOLOCK,
-        TRANS_JOIN_FREEZE,
+        TRANS_ATTACH,
 };
 
 struct btrfs_trans_handle {
@@ -109,7 +109,7 @@ struct btrfs_trans_handle *btrfs_start_transaction_noflush(
                                         struct btrfs_root *root, int num_items);
 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_join_transaction_freeze(struct btrfs_root *root);
+struct btrfs_trans_handle *btrfs_attach_transaction(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,