linux-kernel - Re: [PATCH] drm: Replace drm_modeset_lock/unlock_all with DRM_MODESET_LOCK_ALL

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Message-ID: <CAOw6vbK69aWzti9a7MXNmAfVfJXzzC5g74p4ukSE49MhaV_b3g@mail.gmail.com>
Date:   Thu, 30 Apr 2020 11:37:49 -0400
From:   Sean Paul <seanpaul@...omium.org>
To:     Jani Nikula <jani.nikula@...ux.intel.com>
Cc:     Michal Orzel <michalorzel.eng@...il.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        mripard@...nel.org, tzimmermann@...e.de,
        Dave Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] drm: Replace drm_modeset_lock/unlock_all with
 DRM_MODESET_LOCK_ALL_* helpers

On Wed, Apr 29, 2020 at 4:57 AM Jani Nikula <jani.nikula@...ux.intel.com> wrote:
>
> On Tue, 28 Apr 2020, Michal Orzel <michalorzel.eng@...il.com> wrote:
> > As suggested by the TODO list for the kernel DRM subsystem, replace
> > the deprecated functions that take/drop modeset locks with new helpers.
> >
> > Signed-off-by: Michal Orzel <michalorzel.eng@...il.com>
> > ---
> >  drivers/gpu/drm/drm_mode_object.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_mode_object.c b/drivers/gpu/drm/drm_mode_object.c
> > index 35c2719..901b078 100644
> > --- a/drivers/gpu/drm/drm_mode_object.c
> > +++ b/drivers/gpu/drm/drm_mode_object.c
> > @@ -402,12 +402,13 @@ int drm_mode_obj_get_properties_ioctl(struct drm_device *dev, void *data,
> >  {
> >       struct drm_mode_obj_get_properties *arg = data;
> >       struct drm_mode_object *obj;
> > +     struct drm_modeset_acquire_ctx ctx;
> >       int ret = 0;
> >
> >       if (!drm_core_check_feature(dev, DRIVER_MODESET))
> >               return -EOPNOTSUPP;
> >
> > -     drm_modeset_lock_all(dev);
> > +     DRM_MODESET_LOCK_ALL_BEGIN(dev, ctx, 0, ret);
>
> I cry a little every time I look at the DRM_MODESET_LOCK_ALL_BEGIN and
> DRM_MODESET_LOCK_ALL_END macros. :(
>
> Currently only six users... but there are ~60 calls to
> drm_modeset_lock_all{,_ctx} that I presume are to be replaced. I wonder
> if this will come back and haunt us.
>

What's the alternative? Seems like the options without the macros is
to use incorrect scope or have a bunch of retry/backoff cargo-cult
everywhere (and hope the copy source is done correctly).

Sean

> BR,
> Jani.
>
>
> >
> >       obj = drm_mode_object_find(dev, file_priv, arg->obj_id, arg->obj_type);
> >       if (!obj) {
> > @@ -427,7 +428,7 @@ int drm_mode_obj_get_properties_ioctl(struct drm_device *dev, void *data,
> >  out_unref:
> >       drm_mode_object_put(obj);
> >  out:
> > -     drm_modeset_unlock_all(dev);
> > +     DRM_MODESET_LOCK_ALL_END(ctx, ret);
> >       return ret;
> >  }
> >
> > @@ -449,12 +450,13 @@ static int set_property_legacy(struct drm_mode_object *obj,
> >  {
> >       struct drm_device *dev = prop->dev;
> >       struct drm_mode_object *ref;
> > +     struct drm_modeset_acquire_ctx ctx;
> >       int ret = -EINVAL;
> >
> >       if (!drm_property_change_valid_get(prop, prop_value, &ref))
> >               return -EINVAL;
> >
> > -     drm_modeset_lock_all(dev);
> > +     DRM_MODESET_LOCK_ALL_BEGIN(dev, ctx, 0, ret);
> >       switch (obj->type) {
> >       case DRM_MODE_OBJECT_CONNECTOR:
> >               ret = drm_connector_set_obj_prop(obj, prop, prop_value);
> > @@ -468,7 +470,7 @@ static int set_property_legacy(struct drm_mode_object *obj,
> >               break;
> >       }
> >       drm_property_change_valid_put(prop, ref);
> > -     drm_modeset_unlock_all(dev);
> > +     DRM_MODESET_LOCK_ALL_END(ctx, ret);
> >
> >       return ret;
> >  }
>
> --
> Jani Nikula, Intel Open Source Graphics Center