Re: task btrfs-cleaner:770 blocked for more than 120 seconds.

["Михаил Гаврилов" <mikhail.v.gavrilov@gmail.com>]

Thanks guys, I appreciate your's work.
In which kernel this patch would landed?

--
Best Regards,
Mike Gavrilov.


2016-02-12 0:18 GMT+05:00 Liu Bo <bo.li.liu@oracle.com>:
>
> Really appreciate for collecting these, it should be helpful.
>
> Unfortunately I still could not figure out who's holding fs tree's root WRITE_LOCK so that others are blocked.
>
> A possible bug in log code (the follwing patch addressed it),
>
> - log_new_dir_dentries() is holding log tree's leaf READ_LOCK and may try
>   to get fs tree's READ_LOCK via btrfs_iget() -> btrfs_lookup().
>   (This is shown in the backtrac)
>
> - btrfs_log_inode() can call btrfs_search_forward() to get fs tree's
>   leaf READ_LOCK and then call copy_items() -> btrfs_insert_empty_items()
>   to acquire WRITE_LOCK of log tree's leaf and leaf's parent.
>   (In the backtrace, this is blocked by item 1 because log_new_dir_dentries is
>   holding a log tree leaf's READ_LOCK() which happens to be sibling to
>   the leaf that btrfs_insert_empty_items() is accessing, when doing
>   split_leaf() it needs to get the sibling's WRITE_LOCK(). )
>
> Thanks,
>
> -liubo
>
> diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
> index 323e12c..4a64fdd 100644
> --- a/fs/btrfs/tree-log.c
> +++ b/fs/btrfs/tree-log.c
> @@ -4956,6 +4956,7 @@ process_leaf:
>                         if (di_key.type == BTRFS_ROOT_ITEM_KEY)
>                                 continue;
>
> +                       btrfs_release_path(path);
>                         di_inode = btrfs_iget(root->fs_info->sb, &di_key,
>                                               root, NULL);
>                         if (IS_ERR(di_inode)) {
> @@ -4971,7 +4972,6 @@ process_leaf:
>                         ctx->log_new_dentries = false;
>                         if (type == BTRFS_FT_DIR)
>                                 log_mode = LOG_INODE_ALL;
> -                       btrfs_release_path(path);
>                         ret = btrfs_log_inode(trans, root, di_inode,
>                                               log_mode, 0, LLONG_MAX, ctx);
>                         iput(di_inode);
>
>