On Mon, Feb 25, 2019 at 07:09:02PM +0000, Filipe Manana wrote: > On Mon, Feb 25, 2019 at 6:58 PM David Sterba <[email protected]> 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 <[email protected]> > > --- > > 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.
