Re: [PATCH 04/14] drm/msm: Add priv->mm_lock to protect active/inactive lists

[Rob Clark <robdclark@gmail.com>]

On Sun, Oct 4, 2020 at 3:15 PM Daniel Vetter <daniel@ffwll.ch> wrote:
>
> On Sun, Oct 4, 2020 at 9:21 PM Rob Clark <robdclark@gmail.com> wrote:
> >
> > From: Rob Clark <robdclark@chromium.org>
> >
> > Rather than relying on the big dev->struct_mutex hammer, introduce a
> > more specific lock for protecting the bo lists.
> >
> > Signed-off-by: Rob Clark <robdclark@chromium.org>
> > ---
> >  drivers/gpu/drm/msm/msm_debugfs.c      |  7 +++++++
> >  drivers/gpu/drm/msm/msm_drv.c          |  1 +
> >  drivers/gpu/drm/msm/msm_drv.h          | 13 +++++++++++-
> >  drivers/gpu/drm/msm/msm_gem.c          | 28 +++++++++++++++-----------
> >  drivers/gpu/drm/msm/msm_gem_shrinker.c | 12 +++++++++++
> >  drivers/gpu/drm/msm/msm_gpu.h          |  5 ++++-
> >  6 files changed, 52 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/msm_debugfs.c b/drivers/gpu/drm/msm/msm_debugfs.c
> > index ee2e270f464c..64afbed89821 100644
> > --- a/drivers/gpu/drm/msm/msm_debugfs.c
> > +++ b/drivers/gpu/drm/msm/msm_debugfs.c
> > @@ -112,6 +112,11 @@ static int msm_gem_show(struct drm_device *dev, struct seq_file *m)
> >  {
> >         struct msm_drm_private *priv = dev->dev_private;
> >         struct msm_gpu *gpu = priv->gpu;
> > +       int ret;
> > +
> > +       ret = mutex_lock_interruptible(&priv->mm_lock);
> > +       if (ret)
> > +               return ret;
> >
> >         if (gpu) {
> >                 seq_printf(m, "Active Objects (%s):\n", gpu->name);
> > @@ -121,6 +126,8 @@ static int msm_gem_show(struct drm_device *dev, struct seq_file *m)
> >         seq_printf(m, "Inactive Objects:\n");
> >         msm_gem_describe_objects(&priv->inactive_list, m);
> >
> > +       mutex_unlock(&priv->mm_lock);
> > +
> >         return 0;
> >  }
> >
> > diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> > index 49685571dc0e..dc6efc089285 100644
> > --- a/drivers/gpu/drm/msm/msm_drv.c
> > +++ b/drivers/gpu/drm/msm/msm_drv.c
> > @@ -441,6 +441,7 @@ static int msm_drm_init(struct device *dev, struct drm_driver *drv)
> >         init_llist_head(&priv->free_list);
> >
> >         INIT_LIST_HEAD(&priv->inactive_list);
> > +       mutex_init(&priv->mm_lock);
>
> I highly recommend you drop a
>
> fs_reclaim_acquire(GFP_KERNEL);
> might_lock(&priv->mm_lock);
> fs_reclaim_release(GFP_KERNEL);
>
> in here to teach lockdep about your ordering against the shrinker.
> Gives you full testing every boot, even if your shrinker never gets
> called.

Good idea..

(tbf, I have tested this with android+lockdep which pretty is great
shrinker exercise.. but immediate notification of future problems is a
good plan)

BR,
-R