linux-kernel - Re: [PATCH 3/4] drm/msm: Fix debugfs deadlock

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Date:   Wed, 31 Mar 2021 16:13:13 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        Rob Clark <robdclark@...omium.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jordan Crouse <jordan@...micpenguin.net>,
        "Kristian H. Kristensen" <hoegsberg@...gle.com>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <linux-arm-msm@...r.kernel.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <freedreno@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] drm/msm: Fix debugfs deadlock

Hi,

On Wed, Mar 31, 2021 at 3:14 PM Rob Clark <robdclark@...il.com> wrote:
>
> @@ -111,23 +111,15 @@ static const struct file_operations msm_gpu_fops = {
>  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);
> +       ret = mutex_lock_interruptible(&priv->obj_lock);
>         if (ret)
>                 return ret;
>
> -       if (gpu) {
> -               seq_printf(m, "Active Objects (%s):\n", gpu->name);
> -               msm_gem_describe_objects(&gpu->active_list, m);
> -       }
> -
> -       seq_printf(m, "Inactive Objects:\n");
> -       msm_gem_describe_objects(&priv->inactive_dontneed, m);
> -       msm_gem_describe_objects(&priv->inactive_willneed, m);
> +       msm_gem_describe_objects(&priv->objects, m);

I guess we no longer sort the by Active and Inactive but that doesn't
really matter?


> @@ -174,7 +174,13 @@ struct msm_drm_private {
>         struct msm_rd_state *hangrd;   /* debugfs to dump hanging submits */
>         struct msm_perf_state *perf;
>
> -       /*
> +       /**
> +        * List of all GEM objects (mainly for debugfs, protected by obj_lock

It wouldn't hurt to talk about lock ordering here? Like: "If we need
the "obj_lock" and a "gem_lock" at the same time we always grab the
"obj_lock" first.

> @@ -60,13 +60,20 @@ struct msm_gem_object {
>          */
>         uint8_t vmap_count;
>
> -       /* And object is either:
> -        *  inactive - on priv->inactive_list
> +       /**
> +        * Node in list of all objects (mainly for debugfs, protected by
> +        * struct_mutex

Not "struct_mutex" in comment, right? Maybe "obj_lock" I think?

-Doug