Re: [PATCH 01/35] btrfs: add btrfs_delete_ref_head helper

Nikolay Borisov
2018-08-31T12:04:00Z

On 30.08.2018 20:41, Josef Bacik wrote:
> From: Josef Bacik <jbacik@fb.com>
>
> We do this dance in cleanup_ref_head and check_ref_cleanup, unify it
> into a helper and cleanup the calling functions.
>
> Signed-off-by: Josef Bacik <jbacik@fb.com>
> ---
> fs/btrfs/delayed-ref.c | 14 ++++++++++++++
> fs/btrfs/delayed-ref.h | 3 ++-
> fs/btrfs/extent-tree.c | 24 ++++--------------------
> 3 files changed, 20 insertions(+), 21 deletions(-)
>
> diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
> index 62ff545ba1f7..3a9e4ac21794 100644
> --- a/fs/btrfs/delayed-ref.c
> +++ b/fs/btrfs/delayed-ref.c
> @@ -393,6 +393,20 @@ btrfs_select_ref_head(struct btrfs_trans_handle *trans)
> return head;
> }
>
> +void btrfs_delete_ref_head(struct btrfs_delayed_ref_root *delayed_refs,
> + struct btrfs_delayed_ref_head *head)
> +{
> + lockdep_assert_held(&delayed_refs->lock);
> + lockdep_assert_held(&head->lock);
> +
> + rb_erase(&head->href_node, &delayed_refs->href_root);
> + RB_CLEAR_NODE(&head->href_node);
> + atomic_dec(&delayed_refs->num_entries);
> + delayed_refs->num_heads--;
> + if (head->processing == 0)
> + delayed_refs->num_heads_ready--;
> +}
> +
> /*
> * Helper to insert the ref_node to the tail or merge with tail.
> *
> diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h
> index d9f2a4ebd5db..7769177b489e 100644
> --- a/fs/btrfs/delayed-ref.h
> +++ b/fs/btrfs/delayed-ref.h
> @@ -261,7 +261,8 @@ static inline void btrfs_delayed_ref_unlock(struct btrfs_delayed_ref_head *head)
> {
> mutex_unlock(&head->mutex);
> }
> -
> +void btrfs_delete_ref_head(struct btrfs_delayed_ref_root *delayed_refs,
> + struct btrfs_delayed_ref_head *head);
>
> struct btrfs_delayed_ref_head *
> btrfs_select_ref_head(struct btrfs_trans_handle *trans);
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index f77226d8020a..6799950fa057 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -2492,12 +2492,9 @@ static int cleanup_ref_head(struct btrfs_trans_handle *trans,
> spin_unlock(&delayed_refs->lock);
> return 1;
> }
> - delayed_refs->num_heads--;
> - rb_erase(&head->href_node, &delayed_refs->href_root);
> - RB_CLEAR_NODE(&head->href_node);
> - spin_unlock(&head->lock);
> + btrfs_delete_ref_head(delayed_refs, head);
> spin_unlock(&delayed_refs->lock);
> - atomic_dec(&delayed_refs->num_entries);
> + spin_unlock(&head->lock);
>

Again, the feedback of reversed lock-order is not addressed:

https://www.spinics.net/lists/linux-btrfs/msg80482.html

> trace_run_delayed_ref_head(fs_info, head, 0);
>
> @@ -6984,22 +6981,9 @@ static noinline int check_ref_cleanup(struct btrfs_trans_handle *trans,
> if (!mutex_trylock(&head->mutex))
> goto out;
>
> - /*
> - * at this point we have a head with no other entries. Go
> - * ahead and process it.
> - */
> - rb_erase(&head->href_node, &delayed_refs->href_root);
> - RB_CLEAR_NODE(&head->href_node);
> - atomic_dec(&delayed_refs->num_entries);
> -
> - /*
> - * we don't take a ref on the node because we're removing it from the
> - * tree, so we just steal the ref the tree was holding.
> - */
> - delayed_refs->num_heads--;
> - if (head->processing == 0)
> - delayed_refs->num_heads_ready--;
> + btrfs_delete_ref_head(delayed_refs, head);
> head->processing = 0;
> +
> spin_unlock(&head->lock);
> spin_unlock(&delayed_refs->lock);
>
>