Re: [PATCH] drm/nouveau/fbcon: fix deadlock with FBIOPUT_CON2FBMAP

[Lukas Wunner <lukas-JFq808J9C/izQB+pC5nmwQ@public.gmane.org>]

On Tue, Jul 12, 2016 at 06:49:34PM +0200, Peter Wu wrote:
> The FBIOPUT_CON2FBMAP ioctl takes a console_lock(). When this is called
> while nouveau was runtime suspended, a deadlock would occur due to
> nouveau_fbcon_set_suspend also trying to obtain console_lock().
> 
> Fix this by delaying the drm_fb_helper_set_suspend call. Based on the
> i915 code (which was done for performance reasons though).
> 
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Peter Wu <peter@lekensteyn.nl>
> ---
> Tested on top of v4.7-rc5, the deadlock is gone.

Hm, how did you trigger this deadlock?

Thanks,

Lukas

> ---
>  drivers/gpu/drm/nouveau/nouveau_drm.c   |  4 +--
>  drivers/gpu/drm/nouveau/nouveau_drv.h   |  1 +
>  drivers/gpu/drm/nouveau/nouveau_fbcon.c | 54 ++++++++++++++++++++++++++++-----
>  drivers/gpu/drm/nouveau/nouveau_fbcon.h |  2 +-
>  4 files changed, 50 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c b/drivers/gpu/drm/nouveau/nouveau_drm.c
> index 11f8dd9..f9a2c10 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_drm.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_drm.c
> @@ -552,7 +552,7 @@ nouveau_do_suspend(struct drm_device *dev, bool runtime)
>  
>  	if (dev->mode_config.num_crtc) {
>  		NV_INFO(drm, "suspending console...\n");
> -		nouveau_fbcon_set_suspend(dev, 1);
> +		nouveau_fbcon_set_suspend(dev, FBINFO_STATE_SUSPENDED, true);
>  		NV_INFO(drm, "suspending display...\n");
>  		ret = nouveau_display_suspend(dev, runtime);
>  		if (ret)
> @@ -635,7 +635,7 @@ nouveau_do_resume(struct drm_device *dev, bool runtime)
>  		NV_INFO(drm, "resuming display...\n");
>  		nouveau_display_resume(dev, runtime);
>  		NV_INFO(drm, "resuming console...\n");
> -		nouveau_fbcon_set_suspend(dev, 0);
> +		nouveau_fbcon_set_suspend(dev, FBINFO_STATE_RUNNING, false);
>  	}
>  
>  	return 0;
> diff --git a/drivers/gpu/drm/nouveau/nouveau_drv.h b/drivers/gpu/drm/nouveau/nouveau_drv.h
> index 822a021..a743d19 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_drv.h
> +++ b/drivers/gpu/drm/nouveau/nouveau_drv.h
> @@ -147,6 +147,7 @@ struct nouveau_drm {
>  	struct nouveau_channel *channel;
>  	struct nvkm_gpuobj *notify;
>  	struct nouveau_fbdev *fbcon;
> +	struct work_struct fbdev_suspend_work;
>  	struct nvif_object nvsw;
>  	struct nvif_object ntfy;
>  	struct nvif_notify flip;
> diff --git a/drivers/gpu/drm/nouveau/nouveau_fbcon.c b/drivers/gpu/drm/nouveau/nouveau_fbcon.c
> index d1f248f..089156a 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_fbcon.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_fbcon.c
> @@ -492,19 +492,53 @@ static const struct drm_fb_helper_funcs nouveau_fbcon_helper_funcs = {
>  	.fb_probe = nouveau_fbcon_create,
>  };
>  
> +static void nouveau_fbcon_suspend_worker(struct work_struct *work)
> +{
> +	nouveau_fbcon_set_suspend(container_of(work,
> +					       struct nouveau_drm,
> +					       fbdev_suspend_work)->dev,
> +				  FBINFO_STATE_RUNNING,
> +				  true);
> +}
> +
>  void
> -nouveau_fbcon_set_suspend(struct drm_device *dev, int state)
> +nouveau_fbcon_set_suspend(struct drm_device *dev, int state, bool synchronous)
>  {
>  	struct nouveau_drm *drm = nouveau_drm(dev);
> -	if (drm->fbcon) {
> -		console_lock();
> -		if (state == FBINFO_STATE_RUNNING)
> -			nouveau_fbcon_accel_restore(dev);
> -		drm_fb_helper_set_suspend(&drm->fbcon->helper, state);
> +	if (!drm->fbcon)
> +		return;
> +
> +	if (synchronous) {
> +		/* Flush any pending work to turn the console on, and then
> +		 * wait to turn it off. It must be synchronous as we are
> +		 * about to suspend or unload the driver.
> +		 *
> +		 * Note that from within the work-handler, we cannot flush
> +		 * ourselves, so only flush outstanding work upon suspend!
> +		 */
>  		if (state != FBINFO_STATE_RUNNING)
> -			nouveau_fbcon_accel_save_disable(dev);
> -		console_unlock();
> +			flush_work(&drm->fbdev_suspend_work);
> +		console_lock();
> +	} else {
> +		/*
> +		 * The console lock can be pretty contented on resume due
> +		 * to all the printk activity.  Try to keep it out of the hot
> +		 * path of resume if possible.  This also prevents a deadlock
> +		 * with FBIOPUT_CON2FBMAP.
> +		 */
> +		WARN_ON(state != FBINFO_STATE_RUNNING);
> +		if (!console_trylock()) {
> +			schedule_work(&drm->fbdev_suspend_work);
> +			return;
> +		}
>  	}
> +
> +	if (state == FBINFO_STATE_RUNNING)
> +		nouveau_fbcon_accel_restore(dev);
> +	drm_fb_helper_set_suspend(&drm->fbcon->helper, state);
> +	if (state != FBINFO_STATE_RUNNING)
> +		nouveau_fbcon_accel_save_disable(dev);
> +	console_unlock();
>  }
>  
>  int
> @@ -526,6 +560,8 @@ nouveau_fbcon_init(struct drm_device *dev)
>  	fbcon->dev = dev;
>  	drm->fbcon = fbcon;
>  
> +	INIT_WORK(&drm->fbdev_suspend_work, nouveau_fbcon_suspend_worker);
> +
>  	drm_fb_helper_prepare(dev, &fbcon->helper, &nouveau_fbcon_helper_funcs);
>  
>  	ret = drm_fb_helper_init(dev, &fbcon->helper,
> @@ -571,6 +607,8 @@ nouveau_fbcon_fini(struct drm_device *dev)
>  	if (!drm->fbcon)
>  		return;
>  
> +	flush_work(&drm->fbdev_suspend_work);
> +
>  	nouveau_fbcon_accel_fini(dev);
>  	nouveau_fbcon_destroy(dev, drm->fbcon);
>  	kfree(drm->fbcon);
> diff --git a/drivers/gpu/drm/nouveau/nouveau_fbcon.h b/drivers/gpu/drm/nouveau/nouveau_fbcon.h
> index ca77ad0..34b2504 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_fbcon.h
> +++ b/drivers/gpu/drm/nouveau/nouveau_fbcon.h
> @@ -66,7 +66,7 @@ void nouveau_fbcon_gpu_lockup(struct fb_info *info);
>  
>  int nouveau_fbcon_init(struct drm_device *dev);
>  void nouveau_fbcon_fini(struct drm_device *dev);
> -void nouveau_fbcon_set_suspend(struct drm_device *dev, int state);
> +void nouveau_fbcon_set_suspend(struct drm_device *dev, int state, bool synchronous);
>  void nouveau_fbcon_accel_save_disable(struct drm_device *dev);
>  void nouveau_fbcon_accel_restore(struct drm_device *dev);
>  
> -- 
> 2.8.3
> 
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