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

[Liu Bo <bo.li.liu@oracle.com>]

On Fri, Feb 12, 2016 at 02:03:15AM +0500, Михаил Гаврилов wrote:
> Thanks guys, I appreciate your's work.
> In which kernel this patch would landed?

You can try it on your 4.2.3 kernel or the latest 4.5, but I guess it
doesn't not fix the real deadlock you're hitting...

Thanks,

-liubo

> 
> --
> 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);
> >
> >