0002-Btrfs-remove-some-unnecessary-spin_lock-usages.patch

From f4e9494649db16dd5f59b164454b362fbb5f062a Mon Sep 17 00:00:00 2001
From: Wang Shilong <wangsl-fnst@cn.fujitsu.com>
Date: Thu, 28 Mar 2013 12:50:29 +0800
Subject: [PATCH V2 2/6] Btrfs: remove some unnecessary spin_lock usages

We use mutex_lock to protect all the user change operaions.
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 to here.Spin_lock must be fistly
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>
---
 fs/btrfs/qgroup.c |   42 +++++++++++++++---------------------------
 1 files changed, 15 insertions(+), 27 deletions(-)

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index e3598fa..7df372a 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -42,7 +42,6 @@
  *  - limit
  *  - caches fuer ulists
  *  - performance benchmarks
- *  - check all ioctl parameters
  */
 
 /*
@@ -98,7 +97,11 @@ struct btrfs_qgroup_list {
 	struct btrfs_qgroup *member;
 };
 
-/* must be called with qgroup_lock held */
+/*
+ * don't need to be held by spin_lock since
+ * all the quota configurations on memory has been protected
+ * by mutex quota_lock.
+ */
 static struct btrfs_qgroup *find_qgroup_rb(struct btrfs_fs_info *fs_info,
 					   u64 qgroupid)
 {
@@ -793,13 +796,10 @@ int btrfs_quota_enable(struct btrfs_trans_handle *trans,
 	int ret = 0;
 	int slot;
 
-	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;
+		return ret;
 	}
-	spin_unlock(&fs_info->qgroup_lock);
 
 	/*
 	 * initially create the quota tree
@@ -808,7 +808,7 @@ int btrfs_quota_enable(struct btrfs_trans_handle *trans,
 				       BTRFS_QUOTA_TREE_OBJECTID);
 	if (IS_ERR(quota_root)) {
 		ret =  PTR_ERR(quota_root);
-		goto out;
+		return ret;
 	}
 
 	path = btrfs_alloc_path();
@@ -861,14 +861,11 @@ 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)
@@ -883,13 +880,12 @@ 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);
@@ -901,7 +897,6 @@ out_free_root:
 		free_extent_buffer(quota_root->commit_root);
 		kfree(quota_root);
 	}
-out:
 	return ret;
 }
 
@@ -912,11 +907,10 @@ int btrfs_quota_disable(struct btrfs_trans_handle *trans,
 	struct btrfs_root *quota_root;
 	int ret = 0;
 
-	spin_lock(&fs_info->qgroup_lock);
-	if (!fs_info->quota_root) {
-		spin_unlock(&fs_info->qgroup_lock);
+	if (!fs_info->quota_root)
 		return 0;
-	}
+
+	spin_lock(&fs_info->qgroup_lock);
 	fs_info->quota_enabled = 0;
 	fs_info->pending_quota_state = 0;
 	quota_root = fs_info->quota_root;
@@ -1041,15 +1035,12 @@ int btrfs_remove_qgroup(struct btrfs_trans_handle *trans,
 		return -EINVAL;
 
 	/* 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);
+		if (!list_empty(&qgroup->groups) ||
+		    !list_empty(&qgroup->members))
 			return -EBUSY;
-		}
 	}
-	spin_unlock(&fs_info->qgroup_lock);
 
 	ret = del_qgroup_item(trans, quota_root, qgroupid);
 
@@ -1081,20 +1072,17 @@ 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;
+		return ret;
 	}
+	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);
 
 	return ret;
-- 
1.7.7.6