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>

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 57746c1..1cb084e 100644 (file)
--- 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++;