On Mon, Feb 25, 2019 at 07:09:02PM +0000, Filipe Manana wrote:
> On Mon, Feb 25, 2019 at 6:58 PM David Sterba <dsterba@xxxxxxxx> wrote:
> >
> > The allocation happens with GFP_KERNEL after a transaction has been
> > started, this can potentially cause deadlock if reclaim tries to get the
> > memory by flushing filesystem data.
> >
> > The qgroup_ulist is not used during transaction start as the quotas are
> > not yet enabled but to provide the same semantics, use a temporary
> > variable and assign fs_info::qgroup_ulist as before.
> >
> > Signed-off-by: David Sterba <dsterba@xxxxxxxx>
> > ---
> > fs/btrfs/qgroup.c | 14 ++++++++------
> > 1 file changed, 8 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> > index c1cd5558a646..9e49d5e132b8 100644
> > --- a/fs/btrfs/qgroup.c
> > +++ b/fs/btrfs/qgroup.c
> > @@ -887,6 +887,7 @@ int btrfs_quota_enable(struct btrfs_fs_info *fs_info)
> > struct btrfs_key found_key;
> > struct btrfs_qgroup *qgroup = NULL;
> > struct btrfs_trans_handle *trans = NULL;
> > + struct ulist *tmp_ulist;
> > int ret = 0;
> > int slot;
> >
> > @@ -894,6 +895,12 @@ int btrfs_quota_enable(struct btrfs_fs_info *fs_info)
> > if (fs_info->quota_root)
> > goto out;
> >
> > + tmp_ulist = ulist_alloc(GFP_KERNEL);
> > + if (!tmp_ulist) {
> > + ret = -ENOMEM;
> > + goto out;
> > + }
>
> tmp_ulist needs to be freed if starting the transaction below fails.
Right. If I did not try to preserve the semantics (that does not seem to
be necessary), the freeing would happen on qgroup_ulist as before.
Starting transaction uses qgruop_ulist if quotas are enabled, so at this
time of btrfs_quota_enable, this is not yet true. The status bit is set
later.
I'll update the patch with this explanation and drop the temporary
variable.
