Re: [PATCH v2] btrfs: qgroup: preallocate memory before adding a relation

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2024/6/21 03:16, David Sterba 写道:
> There's a transaction joined in the qgroup relation add/remove ioctl and
> any error will lead to abort/error. We could lift the allocation from
> btrfs_add_qgroup_relation() and move it outside of the transaction
> context. The relation deletion does not need that.
>
> The ownership of the structure is moved to the add relation handler.
>
> Signed-off-by: David Sterba <dsterba@suse.com>

Reviewed-by: Qu Wenruo <wqu@suse.com>

Thanks,
Qu
> ---
>
> v2:
> - preallocate only when adding the relation
>
>   fs/btrfs/ioctl.c  | 17 ++++++++++++++++-
>   fs/btrfs/qgroup.c | 25 ++++++++-----------------
>   fs/btrfs/qgroup.h | 11 ++++++++++-
>   3 files changed, 34 insertions(+), 19 deletions(-)
>
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index d28ebabe3720..dc7300f2815f 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -3829,6 +3829,7 @@ static long btrfs_ioctl_qgroup_assign(struct file *file, void __user *arg)
>   	struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
>   	struct btrfs_root *root = BTRFS_I(inode)->root;
>   	struct btrfs_ioctl_qgroup_assign_args *sa;
> +	struct btrfs_qgroup_list *prealloc = NULL;
>   	struct btrfs_trans_handle *trans;
>   	int ret;
>   	int err;
> @@ -3849,14 +3850,27 @@ static long btrfs_ioctl_qgroup_assign(struct file *file, void __user *arg)
>   		goto drop_write;
>   	}
>
> +	if (sa->assign) {
> +		prealloc = kzalloc(sizeof(*prealloc), GFP_KERNEL);
> +		if (!prealloc) {
> +			ret = -ENOMEM;
> +			goto drop_write;
> +		}
> +	}
> +
>   	trans = btrfs_join_transaction(root);
>   	if (IS_ERR(trans)) {
>   		ret = PTR_ERR(trans);
>   		goto out;
>   	}
>
> +	/*
> +	 * Prealloc ownership is moved to the relation handler, there it's used
> +	 * or freed on error.
> +	 */
>   	if (sa->assign) {
> -		ret = btrfs_add_qgroup_relation(trans, sa->src, sa->dst);
> +		ret = btrfs_add_qgroup_relation(trans, sa->src, sa->dst, prealloc);
> +		prealloc = NULL;
>   	} else {
>   		ret = btrfs_del_qgroup_relation(trans, sa->src, sa->dst);
>   	}
> @@ -3873,6 +3887,7 @@ static long btrfs_ioctl_qgroup_assign(struct file *file, void __user *arg)
>   		ret = err;
>
>   out:
> +	kfree(prealloc);
>   	kfree(sa);
>   drop_write:
>   	mnt_drop_write_file(file);
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index 3edbe5bb19c6..4ae01c87e418 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -155,16 +155,6 @@ static inline u64 btrfs_qgroup_get_new_refcnt(const struct btrfs_qgroup *qg, u64
>   	return qg->new_refcnt - seq;
>   }
>
> -/*
> - * glue structure to represent the relations between qgroups.
> - */
> -struct btrfs_qgroup_list {
> -	struct list_head next_group;
> -	struct list_head next_member;
> -	struct btrfs_qgroup *group;
> -	struct btrfs_qgroup *member;
> -};
> -
>   static int
>   qgroup_rescan_init(struct btrfs_fs_info *fs_info, u64 progress_objectid,
>   		   int init_flags);
> @@ -1568,15 +1558,21 @@ static int quick_update_accounting(struct btrfs_fs_info *fs_info,
>   	return ret;
>   }
>
> -int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans, u64 src, u64 dst)
> +/*
> + * Add relation between @src and @dst qgroup. The @prealloc is allocated by the
> + * callers and transferred here (either used or freed on error).
> + */
> +int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans, u64 src, u64 dst,
> +			      struct btrfs_qgroup_list *prealloc)
>   {
>   	struct btrfs_fs_info *fs_info = trans->fs_info;
>   	struct btrfs_qgroup *parent;
>   	struct btrfs_qgroup *member;
>   	struct btrfs_qgroup_list *list;
> -	struct btrfs_qgroup_list *prealloc = NULL;
>   	int ret = 0;
>
> +	ASSERT(prealloc);
> +
>   	/* Check the level of src and dst first */
>   	if (btrfs_qgroup_level(src) >= btrfs_qgroup_level(dst))
>   		return -EINVAL;
> @@ -1601,11 +1597,6 @@ int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans, u64 src, u64 dst
>   		}
>   	}
>
> -	prealloc = kzalloc(sizeof(*list), GFP_NOFS);
> -	if (!prealloc) {
> -		ret = -ENOMEM;
> -		goto out;
> -	}
>   	ret = add_qgroup_relation_item(trans, src, dst);
>   	if (ret)
>   		goto out;
> diff --git a/fs/btrfs/qgroup.h b/fs/btrfs/qgroup.h
> index 95881dcab684..deb479d176a9 100644
> --- a/fs/btrfs/qgroup.h
> +++ b/fs/btrfs/qgroup.h
> @@ -278,6 +278,14 @@ struct btrfs_qgroup {
>   	struct kobject kobj;
>   };
>
> +/* Glue structure to represent the relations between qgroups. */
> +struct btrfs_qgroup_list {
> +	struct list_head next_group;
> +	struct list_head next_member;
> +	struct btrfs_qgroup *group;
> +	struct btrfs_qgroup *member;
> +};
> +
>   struct btrfs_squota_delta {
>   	/* The fstree root this delta counts against. */
>   	u64 root;
> @@ -321,7 +329,8 @@ int btrfs_qgroup_rescan(struct btrfs_fs_info *fs_info);
>   void btrfs_qgroup_rescan_resume(struct btrfs_fs_info *fs_info);
>   int btrfs_qgroup_wait_for_completion(struct btrfs_fs_info *fs_info,
>   				     bool interruptible);
> -int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans, u64 src, u64 dst);
> +int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans, u64 src, u64 dst,
> +			      struct btrfs_qgroup_list *prealloc);
>   int btrfs_del_qgroup_relation(struct btrfs_trans_handle *trans, u64 src,
>   			      u64 dst);
>   int btrfs_create_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid);