Re: [PATCH v2 5/6] drm/atomic: Fix freeing connector/plane state too early by tracking commits, v3.

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On Mon, Sep 04, 2017 at 12:48:37PM +0200, Maarten Lankhorst wrote:
> Currently we neatly track the crtc state, but forget to look at
> plane/connector state.
> 
> When doing a nonblocking modeset, immediately followed by a setprop
> before the modeset completes, the setprop will see the modesets new
> state as the old state and free it.
> 
> This has to be solved by waiting for hw_done on the connector, even
> if it's not assigned to a crtc. When a connector is unbound we take
> the last crtc commit, and when it stays unbound we create a new
> fake crtc commit for that gets signaled on hw_done for all the
> planes/connectors.
> 
> We wait for it the same way as we do for crtc's, which will make
> sure we never run into a use-after-free situation.
> 
> Changes since v1:
> - Only create a single disable commit. (danvet)
> - Fix leak in intel_legacy_cursor_update.
> Changes since v2:
> - Make reference counting in drm_atomic_helper_setup_commit
>   more obvious. (pinchartl)
> - Call cleanup_done for fake commit. (danvet)
> - Add comments to drm_atomic_helper_setup_commit. (danvet, pinchartl)
> - Add comment to drm_atomic_helper_swap_state. (pinchartl)
> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Testcase: kms_atomic_transition.plane-use-after-nonblocking-unbind*
> Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_atomic.c         |   4 +
>  drivers/gpu/drm/drm_atomic_helper.c  | 172 +++++++++++++++++++++++++++++++++--
>  drivers/gpu/drm/i915/intel_display.c |   2 +
>  include/drm/drm_atomic.h             |  12 +++
>  include/drm/drm_connector.h          |   7 ++
>  include/drm/drm_plane.h              |   7 ++
>  6 files changed, 198 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 2cce48f203e0..75f5f74de9bf 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -192,6 +192,10 @@ void drm_atomic_state_default_clear(struct drm_atomic_state *state)
>  	}
>  	state->num_private_objs = 0;
>  
> +	if (state->fake_commit) {
> +		drm_crtc_commit_put(state->fake_commit);
> +		state->fake_commit = NULL;
> +	}
>  }
>  EXPORT_SYMBOL(drm_atomic_state_default_clear);
>  
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 04629d883114..c81d46927a74 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1667,6 +1667,38 @@ static void release_crtc_commit(struct completion *completion)
>  	drm_crtc_commit_put(commit);
>  }
>  
> +static void init_commit(struct drm_crtc_commit *commit, struct drm_crtc *crtc)
> +{
> +	init_completion(&commit->flip_done);
> +	init_completion(&commit->hw_done);
> +	init_completion(&commit->cleanup_done);
> +	INIT_LIST_HEAD(&commit->commit_entry);
> +	kref_init(&commit->ref);
> +	commit->crtc = crtc;
> +}
> +
> +static struct drm_crtc_commit *
> +crtc_or_fake_commit(struct drm_atomic_state *state, struct drm_crtc *crtc)

Bikeshed: Would be nice if this function directly increases the refcount,
instead of imposing this on all callers. Would need a rename too like
crtc_or_fake_commit_get().

But since this bug is randomly killing our hsw CI and causing lots of
noise better to push as-is and polish later on.

Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>

> +{
> +	if (crtc) {
> +		struct drm_crtc_state *new_crtc_state;
> +
> +		new_crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
> +
> +		return new_crtc_state->commit;
> +	}
> +
> +	if (!state->fake_commit) {
> +		state->fake_commit = kzalloc(sizeof(*state->fake_commit), GFP_KERNEL);
> +		if (!state->fake_commit)
> +			return NULL;
> +
> +		init_commit(state->fake_commit, NULL);
> +	}
> +
> +	return state->fake_commit;
> +}
> +
>  /**
>   * drm_atomic_helper_setup_commit - setup possibly nonblocking commit
>   * @state: new modeset state to be committed
> @@ -1715,6 +1747,10 @@ int drm_atomic_helper_setup_commit(struct drm_atomic_state *state,
>  {
>  	struct drm_crtc *crtc;
>  	struct drm_crtc_state *old_crtc_state, *new_crtc_state;
> +	struct drm_connector *conn;
> +	struct drm_connector_state *old_conn_state, *new_conn_state;
> +	struct drm_plane *plane;
> +	struct drm_plane_state *old_plane_state, *new_plane_state;
>  	struct drm_crtc_commit *commit;
>  	int i, ret;
>  
> @@ -1723,12 +1759,7 @@ int drm_atomic_helper_setup_commit(struct drm_atomic_state *state,
>  		if (!commit)
>  			return -ENOMEM;
>  
> -		init_completion(&commit->flip_done);
> -		init_completion(&commit->hw_done);
> -		init_completion(&commit->cleanup_done);
> -		INIT_LIST_HEAD(&commit->commit_entry);
> -		kref_init(&commit->ref);
> -		commit->crtc = crtc;
> +		init_commit(commit, crtc);
>  
>  		new_crtc_state->commit = commit;
>  
> @@ -1764,6 +1795,42 @@ int drm_atomic_helper_setup_commit(struct drm_atomic_state *state,
>  		drm_crtc_commit_get(commit);
>  	}
>  
> +	for_each_oldnew_connector_in_state(state, conn, old_conn_state, new_conn_state, i) {
> +		/* commit tracked through new_crtc_state->commit, no need to do it explicitly */
> +		if (new_conn_state->crtc)
> +			continue;
> +
> +		/* Userspace is not allowed to get ahead of the previous
> +		 * commit with nonblocking ones. */
> +		if (nonblock && old_conn_state->commit &&
> +		    !try_wait_for_completion(&old_conn_state->commit->flip_done))
> +			return -EBUSY;
> +
> +		commit = crtc_or_fake_commit(state, old_conn_state->crtc);
> +		if (!commit)
> +			return -ENOMEM;
> +
> +		new_conn_state->commit = drm_crtc_commit_get(commit);
> +	}
> +
> +	for_each_oldnew_plane_in_state(state, plane, old_plane_state, new_plane_state, i) {
> +		/* commit tracked through new_crtc_state->commit, no need to do it explicitly */
> +		if (new_plane_state->crtc)
> +			continue;
> +
> +		/* Userspace is not allowed to get ahead of the previous
> +		 * commit with nonblocking ones. */
> +		if (nonblock && old_plane_state->commit &&
> +		    !try_wait_for_completion(&old_plane_state->commit->flip_done))
> +			return -EBUSY;
> +
> +		commit = crtc_or_fake_commit(state, old_plane_state->crtc);
> +		if (!commit)
> +			return -ENOMEM;
> +
> +		new_plane_state->commit = drm_crtc_commit_get(commit);
> +	}
> +
>  	return 0;
>  }
>  EXPORT_SYMBOL(drm_atomic_helper_setup_commit);
> @@ -1784,6 +1851,10 @@ void drm_atomic_helper_wait_for_dependencies(struct drm_atomic_state *old_state)
>  {
>  	struct drm_crtc *crtc;
>  	struct drm_crtc_state *old_crtc_state;
> +	struct drm_plane *plane;
> +	struct drm_plane_state *old_plane_state;
> +	struct drm_connector *conn;
> +	struct drm_connector_state *old_conn_state;
>  	struct drm_crtc_commit *commit;
>  	int i;
>  	long ret;
> @@ -1808,6 +1879,48 @@ void drm_atomic_helper_wait_for_dependencies(struct drm_atomic_state *old_state)
>  			DRM_ERROR("[CRTC:%d:%s] flip_done timed out\n",
>  				  crtc->base.id, crtc->name);
>  	}
> +
> +	for_each_old_connector_in_state(old_state, conn, old_conn_state, i) {
> +		commit = old_conn_state->commit;
> +
> +		if (!commit)
> +			continue;
> +
> +		ret = wait_for_completion_timeout(&commit->hw_done,
> +						  10*HZ);
> +		if (ret == 0)
> +			DRM_ERROR("[CONNECTOR:%d:%s] hw_done timed out\n",
> +				  conn->base.id, conn->name);
> +
> +		/* Currently no support for overwriting flips, hence
> +		 * stall for previous one to execute completely. */
> +		ret = wait_for_completion_timeout(&commit->flip_done,
> +						  10*HZ);
> +		if (ret == 0)
> +			DRM_ERROR("[CONNECTOR:%d:%s] flip_done timed out\n",
> +				  conn->base.id, conn->name);
> +	}
> +
> +	for_each_old_plane_in_state(old_state, plane, old_plane_state, i) {
> +		commit = old_plane_state->commit;
> +
> +		if (!commit)
> +			continue;
> +
> +		ret = wait_for_completion_timeout(&commit->hw_done,
> +						  10*HZ);
> +		if (ret == 0)
> +			DRM_ERROR("[PLANE:%d:%s] hw_done timed out\n",
> +				  plane->base.id, plane->name);
> +
> +		/* Currently no support for overwriting flips, hence
> +		 * stall for previous one to execute completely. */
> +		ret = wait_for_completion_timeout(&commit->flip_done,
> +						  10*HZ);
> +		if (ret == 0)
> +			DRM_ERROR("[PLANE:%d:%s] flip_done timed out\n",
> +				  plane->base.id, plane->name);
> +	}
>  }
>  EXPORT_SYMBOL(drm_atomic_helper_wait_for_dependencies);
>  
> @@ -1842,6 +1955,11 @@ void drm_atomic_helper_commit_hw_done(struct drm_atomic_state *old_state)
>  		WARN_ON(new_crtc_state->event);
>  		complete_all(&commit->hw_done);
>  	}
> +
> +	if (old_state->fake_commit) {
> +		complete_all(&old_state->fake_commit->hw_done);
> +		complete_all(&old_state->fake_commit->flip_done);
> +	}
>  }
>  EXPORT_SYMBOL(drm_atomic_helper_commit_hw_done);
>  
> @@ -1875,6 +1993,9 @@ void drm_atomic_helper_commit_cleanup_done(struct drm_atomic_state *old_state)
>  		list_del(&commit->commit_entry);
>  		spin_unlock(&crtc->commit_lock);
>  	}
> +
> +	if (old_state->fake_commit)
> +		complete_all(&old_state->fake_commit->cleanup_done);
>  }
>  EXPORT_SYMBOL(drm_atomic_helper_commit_cleanup_done);
>  
> @@ -2254,6 +2375,15 @@ int drm_atomic_helper_swap_state(struct drm_atomic_state *state,
>  	struct drm_private_state *old_obj_state, *new_obj_state;
>  
>  	if (stall) {
> +		/*
> +		 * We have to stall for hw_done here before
> +		 * drm_atomic_helper_wait_for_dependencies() because flip
> +		 * depth > 1 is not yet supported by all drivers. As long as
> +		 * obj->state is directly dereferenced anywhere in the drivers
> +		 * atomic_commit_tail function, then it's unsafe to swap state
> +		 * before drm_atomic_helper_commit_hw_done() is called.
> +		 */
> +
>  		for_each_old_crtc_in_state(state, crtc, old_crtc_state, i) {
>  			commit = old_crtc_state->commit;
>  
> @@ -2264,6 +2394,28 @@ int drm_atomic_helper_swap_state(struct drm_atomic_state *state,
>  			if (ret)
>  				return ret;
>  		}
> +
> +		for_each_old_connector_in_state(state, connector, old_conn_state, i) {
> +			commit = old_conn_state->commit;
> +
> +			if (!commit)
> +				continue;
> +
> +			ret = wait_for_completion_interruptible(&commit->hw_done);
> +			if (ret)
> +				return ret;
> +		}
> +
> +		for_each_old_plane_in_state(state, plane, old_plane_state, i) {
> +			commit = old_plane_state->commit;
> +
> +			if (!commit)
> +				continue;
> +
> +			ret = wait_for_completion_interruptible(&commit->hw_done);
> +			if (ret)
> +				return ret;
> +		}
>  	}
>  
>  	for_each_oldnew_connector_in_state(state, connector, old_conn_state, new_conn_state, i) {
> @@ -3246,6 +3398,7 @@ void __drm_atomic_helper_plane_duplicate_state(struct drm_plane *plane,
>  		drm_framebuffer_get(state->fb);
>  
>  	state->fence = NULL;
> +	state->commit = NULL;
>  }
>  EXPORT_SYMBOL(__drm_atomic_helper_plane_duplicate_state);
>  
> @@ -3287,6 +3440,9 @@ void __drm_atomic_helper_plane_destroy_state(struct drm_plane_state *state)
>  
>  	if (state->fence)
>  		dma_fence_put(state->fence);
> +
> +	if (state->commit)
> +		drm_crtc_commit_put(state->commit);
>  }
>  EXPORT_SYMBOL(__drm_atomic_helper_plane_destroy_state);
>  
> @@ -3365,6 +3521,7 @@ __drm_atomic_helper_connector_duplicate_state(struct drm_connector *connector,
>  	memcpy(state, connector->state, sizeof(*state));
>  	if (state->crtc)
>  		drm_connector_get(connector);
> +	state->commit = NULL;
>  }
>  EXPORT_SYMBOL(__drm_atomic_helper_connector_duplicate_state);
>  
> @@ -3491,6 +3648,9 @@ __drm_atomic_helper_connector_destroy_state(struct drm_connector_state *state)
>  {
>  	if (state->crtc)
>  		drm_connector_put(state->connector);
> +
> +	if (state->commit)
> +		drm_crtc_commit_put(state->commit);
>  }
>  EXPORT_SYMBOL(__drm_atomic_helper_connector_destroy_state);
>  
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index a6cf1c20c712..7abbc761a635 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -13132,8 +13132,10 @@ intel_legacy_cursor_update(struct drm_plane *plane,
>  
>  	/* Swap plane state */
>  	new_plane_state->fence = old_plane_state->fence;
> +	new_plane_state->commit = old_plane_state->commit;
>  	*to_intel_plane_state(old_plane_state) = *to_intel_plane_state(new_plane_state);
>  	new_plane_state->fence = NULL;
> +	new_plane_state->commit = NULL;
>  	new_plane_state->fb = old_fb;
>  	to_intel_plane_state(new_plane_state)->vma = NULL;
>  
> diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> index a80a8dadef00..07a71daa3582 100644
> --- a/include/drm/drm_atomic.h
> +++ b/include/drm/drm_atomic.h
> @@ -236,6 +236,18 @@ struct drm_atomic_state {
>  	struct drm_modeset_acquire_ctx *acquire_ctx;
>  
>  	/**
> +	 * @fake_commit:
> +	 *
> +	 * Used for signaling unbound planes/connectors.
> +	 * When a connector or plane is not bound to any CRTC, it's still important
> +	 * to preserve linearity to prevent the atomic states from being freed to early.
> +	 *
> +	 * This commit (if set) is not bound to any crtc, but will be completed when
> +	 * drm_atomic_helper_commit_hw_done() is called.
> +	 */
> +	struct drm_crtc_commit *fake_commit;
> +
> +	/**
>  	 * @commit_work:
>  	 *
>  	 * Work item which can be used by the driver or helpers to execute the
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index ea8da401c93c..8837649d16e8 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -347,6 +347,13 @@ struct drm_connector_state {
>  
>  	struct drm_atomic_state *state;
>  
> +	/**
> +	 * @commit: Tracks the pending commit to prevent use-after-free conditions.
> +	 *
> +	 * Is only set when @crtc is NULL.
> +	 */
> +	struct drm_crtc_commit *commit;
> +
>  	struct drm_tv_connector_state tv;
>  
>  	/**
> diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
> index 73f90f9d057f..7d96116fd4c4 100644
> --- a/include/drm/drm_plane.h
> +++ b/include/drm/drm_plane.h
> @@ -123,6 +123,13 @@ struct drm_plane_state {
>  	 */
>  	bool visible;
>  
> +	/**
> +	 * @commit: Tracks the pending commit to prevent use-after-free conditions.
> +	 *
> +	 * Is only set when @crtc is NULL.
> +	 */
> +	struct drm_crtc_commit *commit;
> +
>  	struct drm_atomic_state *state;
>  };
>  
> -- 
> 2.11.0
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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