btrfs: qgroup: use atomic operations for btrfs_fs_info::qgroup_flags

Currently we define btrfs_fs_info::qgroup_flags as u64, to match the
on-disk qgroup status item's flag.

But for now we have only 4 bits utilized for that flag, and since it's
u64 we have no way to properly use the existing atomic bit operations
(requires an unsigned long pointer).

This results in a lot of non-atomic operations inside qgroup code. Some
maybe fine as other locks are involved, but still it's not a good
practice.

Remove those non-atomic operations by:

- Re-define btrfs_fs_info::qgroup_flags as unsigned long
- Define BTRFS_QGROUP_STATUS_BIT_* and BTRFS_QGROUP_RUNTIME_BIT_*
  Instead of the old value define the bit number.

- Use set_bit()/clear_bit()/test_bit() to replace open-coded bit
  operations

- Add one extra check at qgroup status item read time
  To make sure the on-disk flag is still inside ULONG_MAX.
  Otherwise reject the status item and disable qgroup.

- Get rid of unnecessary spinlock when checking a single bit

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 2 insertions, 6 deletions

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 39cb01ee441a..1df6340a7123 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -2359,9 +2359,7 @@ static ssize_t qgroup_enabled_show(struct kobject *qgroups_kobj,
 	struct btrfs_fs_info *fs_info = to_fs_info(qgroups_kobj->parent);
 	bool enabled;
 
-	spin_lock(&fs_info->qgroup_lock);
-	enabled = fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_ON;
-	spin_unlock(&fs_info->qgroup_lock);
+	enabled = test_bit(BTRFS_QGROUP_STATUS_BIT_ON, &fs_info->qgroup_flags);
 
 	return sysfs_emit(buf, "%d\n", enabled);
 }
@@ -2401,9 +2399,7 @@ static ssize_t qgroup_inconsistent_show(struct kobject *qgroups_kobj,
 	struct btrfs_fs_info *fs_info = to_fs_info(qgroups_kobj->parent);
 	bool inconsistent;
 
-	spin_lock(&fs_info->qgroup_lock);
-	inconsistent = (fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT);
-	spin_unlock(&fs_info->qgroup_lock);
+	inconsistent = test_bit(BTRFS_QGROUP_STATUS_BIT_INCONSISTENT, &fs_info->qgroup_flags);
 
 	return sysfs_emit(buf, "%d\n", inconsistent);
 }