Btrfs: remove some unnecessary spin_lock usages

We use mutex lock to protect all the user change operations.
So when we are calling find_qgroup_rb() to check whether qgroup
exists, we don't have to hold spin_lock.

Besides, when enabling/disabling quota, it must be single thread
when operations come here. spin lock must be firstly used to
clear quota_root when disabling quota, while enabling quota, spin
lock must be used to complete the last assign work.

Signed-off-by: Wang Shilong <wangsl-fnst@cn.fujitsu.com>
Reviewed-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

1 files changed, 6 insertions, 21 deletions

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 0a1f6861ae9a..49c4e6398f18 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -98,7 +98,7 @@ struct btrfs_qgroup_list {
         struct btrfs_qgroup *member;
 };
 
-/* must be called with qgroup_lock held */
+/* must be called with qgroup_ioctl_lock held */
 static struct btrfs_qgroup *find_qgroup_rb(struct btrfs_fs_info *fs_info,
                                            u64 qgroupid)
 {
@@ -792,13 +792,10 @@ int btrfs_quota_enable(struct btrfs_trans_handle *trans,
         int slot;
 
         mutex_lock(&fs_info->qgroup_ioctl_lock);
-        spin_lock(&fs_info->qgroup_lock);
         if (fs_info->quota_root) {
                 fs_info->pending_quota_state = 1;
-                spin_unlock(&fs_info->qgroup_lock);
                 goto out;
         }
-        spin_unlock(&fs_info->qgroup_lock);
 
         /*
          * initially create the quota tree
@@ -860,14 +857,11 @@ int btrfs_quota_enable(struct btrfs_trans_handle *trans,
                         if (ret)
                                 goto out_free_path;
 
-                        spin_lock(&fs_info->qgroup_lock);
                         qgroup = add_qgroup_rb(fs_info, found_key.offset);
                         if (IS_ERR(qgroup)) {
-                                spin_unlock(&fs_info->qgroup_lock);
                                 ret = PTR_ERR(qgroup);
                                 goto out_free_path;
                         }
-                        spin_unlock(&fs_info->qgroup_lock);
                 }
                 ret = btrfs_next_item(tree_root, path);
                 if (ret < 0)
@@ -882,13 +876,12 @@ out_add_root:
         if (ret)
                 goto out_free_path;
 
-        spin_lock(&fs_info->qgroup_lock);
         qgroup = add_qgroup_rb(fs_info, BTRFS_FS_TREE_OBJECTID);
         if (IS_ERR(qgroup)) {
-                spin_unlock(&fs_info->qgroup_lock);
                 ret = PTR_ERR(qgroup);
                 goto out_free_path;
         }
+        spin_lock(&fs_info->qgroup_lock);
         fs_info->quota_root = quota_root;
         fs_info->pending_quota_state = 1;
         spin_unlock(&fs_info->qgroup_lock);
@@ -913,11 +906,9 @@ int btrfs_quota_disable(struct btrfs_trans_handle *trans,
         int ret = 0;
 
         mutex_lock(&fs_info->qgroup_ioctl_lock);
-        spin_lock(&fs_info->qgroup_lock);
-        if (!fs_info->quota_root) {
-                spin_unlock(&fs_info->qgroup_lock);
+        if (!fs_info->quota_root)
                 goto out;
-        }
+        spin_lock(&fs_info->qgroup_lock);
         fs_info->quota_enabled = 0;
         fs_info->pending_quota_state = 0;
         quota_root = fs_info->quota_root;
@@ -1060,16 +1051,13 @@ int btrfs_remove_qgroup(struct btrfs_trans_handle *trans,
         }
 
         /* check if there are no relations to this qgroup */
-        spin_lock(&fs_info->qgroup_lock);
         qgroup = find_qgroup_rb(fs_info, qgroupid);
         if (qgroup) {
                 if (!list_empty(&qgroup->groups) || !list_empty(&qgroup->members)) {
-                        spin_unlock(&fs_info->qgroup_lock);
                         ret = -EBUSY;
                         goto out;
                 }
         }
-        spin_unlock(&fs_info->qgroup_lock);
 
         ret = del_qgroup_item(trans, quota_root, qgroupid);
 
@@ -1106,20 +1094,17 @@ int btrfs_limit_qgroup(struct btrfs_trans_handle *trans,
                        (unsigned long long)qgroupid);
         }
 
-        spin_lock(&fs_info->qgroup_lock);
-
         qgroup = find_qgroup_rb(fs_info, qgroupid);
         if (!qgroup) {
                 ret = -ENOENT;
-                goto unlock;
+                goto out;
         }
+        spin_lock(&fs_info->qgroup_lock);
         qgroup->lim_flags = limit->flags;
         qgroup->max_rfer = limit->max_rfer;
         qgroup->max_excl = limit->max_excl;
         qgroup->rsv_rfer = limit->rsv_rfer;
         qgroup->rsv_excl = limit->rsv_excl;
-
-unlock:
         spin_unlock(&fs_info->qgroup_lock);
 out:
         mutex_unlock(&fs_info->qgroup_ioctl_lock);