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

[Peter Wu]

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 at chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Peter Wu <peter at lekensteyn.nl>
---
Tested on top of v4.7-rc5, the deadlock is gone.
---
 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