On Wed, May 23, 2018 at 10:16:55AM +0800, Su Yue wrote:
> >>> [ 47.692084] kernel BUG at fs/btrfs/locking.c:286!
> >>
> >> I saw the crash too but did not investigate the root cause. So I'll
> >> remove the branch from for-next until it's fixed. Thanks for the report.
> >
> > I think the problem stems from Qu's patch, which sets search_commit_root
> > =1 but doesn't set skip_locking, as a result we don't lock the tree when
> > we obtain a reference to the root node, yet later when traversing the
> > tree due to skip_locking not being set we try to lock it, and this
> > causes btrfs_assert_tree_locked to triggers. Can you test whether the
> > following diff solves the issues:
> >
> >
> > diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> > index bc19a7d11c98..23fadb640c59 100644
> > --- a/fs/btrfs/qgroup.c
> > +++ b/fs/btrfs/qgroup.c
> > @@ -2702,6 +2702,7 @@ static void btrfs_qgroup_rescan_worker(struct
> > btrfs_work *work)
> > * should be recorded by qgroup
> > */
> > path->search_commit_root = 1;
> > + path->skip_locking = 1;
> >
> > err = 0;
> > while (!err && !btrfs_fs_closing(fs_info)) {
> >
> >
> > If it does, this only means we need to make skip_locking = 1 being
> > conditional on search_commit_root being set and this situation should be
> > handled in btrfs_search_slot.
>
> After patching the change, btrfs/139 passes without BUG_ON.
Confirmed, I've added the fixup to for-next, Liu Bo's branch is there to
and the crash did not show up.
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