Btrfs: introduce a mutex lock for btrfs quota operations

The original code has one spin_lock 'qgroup_lock' to protect quota
configurations in memory. If we want to add a BTRFS_QGROUP_INFO_KEY,
it will be added to Btree firstly, and then update configurations in
memory,however, a race condition may happen between these operations.
For example:
	->add_qgroup_info_item()
		->add_qgroup_rb()

For the above case, del_qgroup_info_item() may happen just before
add_qgroup_rb().

What's worse, when we want to add a qgroup relation:
	->add_qgroup_relation_item()
		->add_qgroup_relations()

We don't have any checks whether 'src' and 'dst' exist before
add_qgroup_relation_item(), a race condition can also happen for
the above case.

To avoid race condition and have all the necessary checks, we introduce
a mutex lock 'qgroup_ioctl_lock', and we make all the user change operations
protected by the mutex lock.

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, 3 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 075a8a0e49c4..1a850402937d 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1583,6 +1583,9 @@ struct btrfs_fs_info {
         struct rb_root qgroup_tree;
         spinlock_t qgroup_lock;
 
+        /* protect user change for quota operations */
+        struct mutex qgroup_ioctl_lock;
+
         /* list of dirty qgroups to be written at next commit */
         struct list_head dirty_qgroups;