Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210331221630.488498-1-robdclark@gmail.com> <20210331221630.488498-4-robdclark@gmail.com>
In-Reply-To: <20210331221630.488498-4-robdclark@gmail.com>
From:   Doug Anderson <dianders@chromium.org>
Date:   Wed, 31 Mar 2021 16:13:13 -0700
Message-ID: <CAD=FV=UECYxLXQa_L572eLSVHq7pbxuA0zLvHzYHhCKy8K=9TA@mail.gmail.com>
Subject: Re: [PATCH 3/4] drm/msm: Fix debugfs deadlock
To:     Rob Clark <robdclark@gmail.com>
Cc:     dri-devel <dri-devel@lists.freedesktop.org>,
        Rob Clark <robdclark@chromium.org>,
        Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Jordan Crouse <jordan@cosmicpenguin.net>,
        "Kristian H. Kristensen" <hoegsberg@google.com>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <linux-arm-msm@vger.kernel.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <freedreno@lists.freedesktop.org>,
        open list <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hi,

On Wed, Mar 31, 2021 at 3:14 PM Rob Clark <robdclark@gmail.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