Btrfs: Fix race in running_transaction checks

When a new transaction was started, the code would incorrectly
set the pointer in fs_info before all the data structures were setup.
fsync heavy workloads hit races on the setup of the ordered inode spinlock

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 57746c11eae3..1cb084efd6ed 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -56,7 +56,6 @@ static noinline int join_transaction(struct btrfs_root *root)
                 total_trans++;
                 BUG_ON(!cur_trans);
                 root->fs_info->generation++;
-                root->fs_info->running_transaction = cur_trans;
                 root->fs_info->last_alloc = 0;
                 root->fs_info->last_data_alloc = 0;
                 cur_trans->num_writers = 1;
@@ -74,6 +73,9 @@ static noinline int join_transaction(struct btrfs_root *root)
                 extent_io_tree_init(&cur_trans->dirty_pages,
                                      root->fs_info->btree_inode->i_mapping,
                                      GFP_NOFS);
+                spin_lock(&root->fs_info->new_trans_lock);
+                root->fs_info->running_transaction = cur_trans;
+                spin_unlock(&root->fs_info->new_trans_lock);
         } else {
                 cur_trans->num_writers++;
                 cur_trans->num_joined++;