[PATCH 1/7] Btrfs: introduce a mutex lock for btrfs quota operations

[PATCH 1/7] Btrfs: introduce a mutex lock for btrfs quota operations

[Wang Shilong]

From: Wang Shilong <wangsl-fnst@cn.fujitsu.com>

The original code only has one spin_lock 'qgroup_lock' to protect
quota configurations on memory, if we want to add a BTRFS_QGROUP_INFO_KEY,
it will be added to Btree firstly and then update quota configuration
on memory,this case works ok just because of Btrfs internal btree lock.
However, if we want to add a BTRFS_QGROUP_RELATION_KEY, this will cause
problems, in fact,we need to check 'src' and 'dst' before, without an extra lock,
race conditions can not be avoided.

Holding mutex_lock, we can have the check before operations in safety.
Besides, we can remove some spin_lock usages and ease the burdern
of the global spin_lock.

Signed-off-by: Wang Shilong <wangsl-fnst@cn.fujitsu.com>
Reviewed-by: Miao Xie <miaox@cn.fujitsu.com>
---
 fs/btrfs/ctree.h   |    1 +
 fs/btrfs/disk-io.c |    1 +
 fs/btrfs/ioctl.c   |   13 ++++++++++---
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 6e81860..a7fec8c 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1582,6 +1582,7 @@ struct btrfs_fs_info {
 
 	/* holds configuration and tracking. Protected by qgroup_lock */
 	struct rb_root qgroup_tree;
+	struct mutex quota_lock;
 	spinlock_t qgroup_lock;
 
 	/* list of dirty qgroups to be written at next commit */
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index fe82d08..4552f14 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2250,6 +2250,7 @@ int open_ctree(struct super_block *sb,
 	mutex_init(&fs_info->dev_replace.lock);
 
 	spin_lock_init(&fs_info->qgroup_lock);
+	mutex_init(&fs_info->quota_lock);
 	fs_info->qgroup_tree = RB_ROOT;
 	INIT_LIST_HEAD(&fs_info->dirty_qgroups);
 	fs_info->qgroup_seq = 1;
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 222ce84..0b8ab81 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3693,6 +3693,7 @@ static long btrfs_ioctl_quota_ctl(struct file *file, void __user *arg)
 		goto drop_write;
 	}
 
+	mutex_lock(&root->fs_info->quota_lock);
 	down_read(&root->fs_info->subvol_sem);
 	if (sa->cmd != BTRFS_QUOTA_CTL_RESCAN) {
 		trans = btrfs_start_transaction(root, 2);
@@ -3728,6 +3729,7 @@ static long btrfs_ioctl_quota_ctl(struct file *file, void __user *arg)
 out:
 	kfree(sa);
 	up_read(&root->fs_info->subvol_sem);
+	mutex_unlock(&root->fs_info->quota_lock);
 drop_write:
 	mnt_drop_write_file(file);
 	return ret;
@@ -3754,6 +3756,7 @@ static long btrfs_ioctl_qgroup_assign(struct file *file, void __user *arg)
 		goto drop_write;
 	}
 
+	mutex_lock(&root->fs_info->quota_lock);
 	trans = btrfs_join_transaction(root);
 	if (IS_ERR(trans)) {
 		ret = PTR_ERR(trans);
@@ -3775,6 +3778,7 @@ static long btrfs_ioctl_qgroup_assign(struct file *file, void __user *arg)
 
 out:
 	kfree(sa);
+	mutex_unlock(&root->fs_info->quota_lock);
 drop_write:
 	mnt_drop_write_file(file);
 	return ret;
@@ -3805,11 +3809,11 @@ static long btrfs_ioctl_qgroup_create(struct file *file, void __user *arg)
 		ret = -EINVAL;
 		goto out;
 	}
-
+	mutex_lock(&root->fs_info->quota_lock);
 	trans = btrfs_join_transaction(root);
 	if (IS_ERR(trans)) {
 		ret = PTR_ERR(trans);
-		goto out;
+		goto out_unlock;
 	}
 
 	/* FIXME: check if the IDs really exist */
@@ -3824,6 +3828,8 @@ static long btrfs_ioctl_qgroup_create(struct file *file, void __user *arg)
 	if (err && !ret)
 		ret = err;
 
+out_unlock:
+	mutex_unlock(&root->fs_info->quota_lock);
 out:
 	kfree(sa);
 drop_write:
@@ -3852,7 +3858,7 @@ static long btrfs_ioctl_qgroup_limit(struct file *file, void __user *arg)
 		ret = PTR_ERR(sa);
 		goto drop_write;
 	}
-
+	mutex_lock(&root->fs_info->quota_lock);
 	trans = btrfs_join_transaction(root);
 	if (IS_ERR(trans)) {
 		ret = PTR_ERR(trans);
@@ -3874,6 +3880,7 @@ static long btrfs_ioctl_qgroup_limit(struct file *file, void __user *arg)
 
 out:
 	kfree(sa);
+	mutex_unlock(&root->fs_info->quota_lock);
 drop_write:
 	mnt_drop_write_file(file);
 	return ret;
-- 
1.7.7.6

Re: [PATCH 1/7] Btrfs: introduce a mutex lock for btrfs quota operations

[Wang Shilong]

Hi,

Please ignore this patchset.
V2 has been made and will be sent out soon!

The main change is to use quota configurations 
on memory to speed up ioctls check.

Thanks,
Wang