Btrfs: place ordered operations on a per transaction list

Miao made the ordered operations stuff run async, which introduced a
deadlock where we could get somebody (sync) racing in and committing the
transaction while a commit was already happening.  The new committer would
try and flush ordered operations which would hang waiting for the commit to
finish because it is done asynchronously and no longer inherits the callers
trans handle.  To fix this we need to make the ordered operations list a per
transaction list.  We can get new inodes added to the ordered operation list
by truncating them and then having another process writing to them, so this
makes it so that anybody trying to add an ordered operation _must_ start a
transaction in order to add itself to the list, which will keep new inodes
from getting added to the ordered operations list after we start committing.
This should fix the deadlock and also keeps us from doing a lot more work
than we need to during commit.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>

1 files changed, 6 insertions, 5 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 9fcce54ecde4..e511d9f78c19 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -56,7 +56,8 @@ static void end_workqueue_fn(struct btrfs_work *work);
 static void free_fs_root(struct btrfs_root *root);
 static int btrfs_check_super_valid(struct btrfs_fs_info *fs_info,
                                     int read_only);
-static void btrfs_destroy_ordered_operations(struct btrfs_root *root);
+static void btrfs_destroy_ordered_operations(struct btrfs_transaction *t,
+                                             struct btrfs_root *root);
 static void btrfs_destroy_ordered_extents(struct btrfs_root *root);
 static int btrfs_destroy_delayed_refs(struct btrfs_transaction *trans,
                                       struct btrfs_root *root);
@@ -2029,7 +2030,6 @@ int open_ctree(struct super_block *sb,
         INIT_LIST_HEAD(&fs_info->dead_roots);
         INIT_LIST_HEAD(&fs_info->delayed_iputs);
         INIT_LIST_HEAD(&fs_info->delalloc_inodes);
-        INIT_LIST_HEAD(&fs_info->ordered_operations);
         INIT_LIST_HEAD(&fs_info->caching_block_groups);
         spin_lock_init(&fs_info->delalloc_lock);
         spin_lock_init(&fs_info->trans_lock);
@@ -3538,7 +3538,8 @@ void btrfs_error_commit_super(struct btrfs_root *root)
         btrfs_cleanup_transaction(root);
 }
 
-static void btrfs_destroy_ordered_operations(struct btrfs_root *root)
+static void btrfs_destroy_ordered_operations(struct btrfs_transaction *t,
+                                             struct btrfs_root *root)
 {
         struct btrfs_inode *btrfs_inode;
         struct list_head splice;
@@ -3548,7 +3549,7 @@ static void btrfs_destroy_ordered_operations(struct btrfs_root *root)
         mutex_lock(&root->fs_info->ordered_operations_mutex);
         spin_lock(&root->fs_info->ordered_extent_lock);
 
-        list_splice_init(&root->fs_info->ordered_operations, &splice);
+        list_splice_init(&t->ordered_operations, &splice);
         while (!list_empty(&splice)) {
                 btrfs_inode = list_entry(splice.next, struct btrfs_inode,
                                          ordered_operations);
@@ -3829,7 +3830,7 @@ int btrfs_cleanup_transaction(struct btrfs_root *root)
         while (!list_empty(&list)) {
                 t = list_entry(list.next, struct btrfs_transaction, list);
 
-                btrfs_destroy_ordered_operations(root);
+                btrfs_destroy_ordered_operations(t, root);
 
                 btrfs_destroy_ordered_extents(root);