Re: [PATCH 11/20] ovl: narrow locking in ovl_workdir_create()

["NeilBrown" <neil@brown.name>]

On Fri, 11 Jul 2025, Amir Goldstein wrote:
> On Fri, Jul 11, 2025 at 1:21 AM NeilBrown <neil@brown.name> wrote:
> >
> > In ovl_workdir_create() don't hold the dir lock for the whole time, but
> > only take it when needed.
> >
> > It now gets taken separately for ovl_workdir_cleanup().  A subsequent
> > patch will move the locking into that function.
> >
> > Signed-off-by: NeilBrown <neil@brown.name>
> > ---
> >  fs/overlayfs/super.c | 16 ++++++++++------
> >  1 file changed, 10 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> > index 9cce3251dd83..239ae1946edf 100644
> > --- a/fs/overlayfs/super.c
> > +++ b/fs/overlayfs/super.c
> > @@ -299,8 +299,8 @@ static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
> >         int err;
> >         bool retried = false;
> >
> > -       inode_lock_nested(dir, I_MUTEX_PARENT);
> >  retry:
> > +       inode_lock_nested(dir, I_MUTEX_PARENT);
> >         work = ovl_lookup_upper(ofs, name, ofs->workbasedir, strlen(name));
> >
> >         if (!IS_ERR(work)) {
> > @@ -311,23 +311,27 @@ static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
> >
> >                 if (work->d_inode) {
> >                         err = -EEXIST;
> > +                       inode_unlock(dir);
> >                         if (retried)
> >                                 goto out_dput;
> >
> >                         if (persist)
> > -                               goto out_unlock;
> > +                               goto out;
> >
> >                         retried = true;
> > +                       inode_lock_nested(dir, I_MUTEX_PARENT);
> 
> Feels like this should be parent_lock(ofs->workbasedir, work)
> and parent_lock(ofs->workbasedir, NULL) in retry:

Agreed.

> 
> >                         err = ovl_workdir_cleanup(ofs, dir, mnt, work, 0);
> > +                       inode_unlock(dir);
> >                         dput(work);
> >                         if (err == -EINVAL) {
> >                                 work = ERR_PTR(err);
> > -                               goto out_unlock;
> > +                               goto out;
> >                         }
> >                         goto retry;
> >                 }
> >
> >                 work = ovl_do_mkdir(ofs, dir, work, attr.ia_mode);
> > +               inode_unlock(dir);
> >                 err = PTR_ERR(work);
> >                 if (IS_ERR(work))
> >                         goto out_err;
> > @@ -365,11 +369,11 @@ static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
> >                 if (err)
> >                         goto out_dput;
> >         } else {
> > +               inode_unlock(dir);
> >                 err = PTR_ERR(work);
> >                 goto out_err;
> >         }
> > -out_unlock:
> > -       inode_unlock(dir);
> > +out:
> >         return work;
> >
> >  out_dput:
> > @@ -378,7 +382,7 @@ static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
> >         pr_warn("failed to create directory %s/%s (errno: %i); mounting read-only\n",
> >                 ofs->config.workdir, name, -err);
> >         work = NULL;
> > -       goto out_unlock;
> > +       goto out;
> 
> might as well be return NULL now.

Done.  I got rid of the out: label completely.

NeilBrown

> 
> Thanks,
> Amir.
>