From: Filipe Manana <fdman...@suse.com> We have a race between enabling quotas end subvolume creation that cause subvolume creation to fail with -EINVAL, and the following diagram shows how it happens:
CPU 0 CPU 1 btrfs_ioctl() btrfs_ioctl_quota_ctl() btrfs_quota_enable() mutex_lock(fs_info->qgroup_ioctl_lock) btrfs_ioctl() create_subvol() btrfs_qgroup_inherit() -> save fs_info->quota_root into quota_root -> stores a NULL value -> tries to lock the mutex qgroup_ioctl_lock -> blocks waiting for the task at CPU0 -> sets BTRFS_FS_QUOTA_ENABLED in fs_info -> sets quota_root in fs_info->quota_root (non-NULL value) mutex_unlock(fs_info->qgroup_ioctl_lock) -> checks quota enabled flag is set -> returns -EINVAL because fs_info->quota_root was NULL before it acquired the mutex qgroup_ioctl_lock -> ioctl returns -EINVAL Returning -EINVAL to user space will be confusing if all the arguments passed to the subvolume creation ioctl were valid. Fix it by grabbing the value from fs_info->quota_root after acquiring the mutex. Signed-off-by: Filipe Manana <fdman...@suse.com> --- fs/btrfs/qgroup.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c index ae1358253b7b..0bdf28499790 100644 --- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -2250,7 +2250,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid, int i; u64 *i_qgroups; struct btrfs_fs_info *fs_info = trans->fs_info; - struct btrfs_root *quota_root = fs_info->quota_root; + struct btrfs_root *quota_root; struct btrfs_qgroup *srcgroup; struct btrfs_qgroup *dstgroup; u32 level_size = 0; @@ -2260,6 +2260,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid, if (!test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags)) goto out; + quota_root = fs_info->quota_root; if (!quota_root) { ret = -EINVAL; goto out; -- 2.11.0