FAILED: patch "[PATCH] drm/nouveau: Fix deadlock on runtime suspend" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Lukas Wunner <[email protected]>
Date: Sun, 11 Feb 2018 10:38:28 +0100
Subject: [PATCH] drm/nouveau: Fix deadlock on runtime suspend

nouveau's ->runtime_suspend hook calls drm_kms_helper_poll_disable(), which waits for the output poll worker to finish if it's running.

The output poll worker meanwhile calls pm_runtime_get_sync() in nouveau_connector_detect() which waits for the ongoing suspend to finish, causing a deadlock.

Fix by not acquiring a runtime PM ref if nouveau_connector_detect() is called in the output poll worker's context. This is safe because the poll worker is only enabled while runtime active and we know that ->runtime_suspend waits for it to finish.

Other contexts calling nouveau_connector_detect() do require a runtime PM ref, these comprise:

status_store() drm sysfs interface
->fill_modes drm callback
drm_fb_helper_probe_connector_modes()
drm_mode_getconnector()
nouveau_connector_hotplug()
nouveau_display_hpd_work()
nv17_tv_set_property()

Stack trace for posterity:

  INFO: task kworker/0:1:58 blocked for more than 120 seconds.
  Workqueue: events output_poll_execute [drm_kms_helper]
  Call Trace:
   schedule+0x28/0x80
   rpm_resume+0x107/0x6e0
   __pm_runtime_resume+0x47/0x70
   nouveau_connector_detect+0x7e/0x4a0 [nouveau]
   nouveau_connector_detect_lvds+0x132/0x180 [nouveau]
   drm_helper_probe_detect_ctx+0x85/0xd0 [drm_kms_helper]
   output_poll_execute+0x11e/0x1c0 [drm_kms_helper]
   process_one_work+0x184/0x380
   worker_thread+0x2e/0x390

  INFO: task kworker/0:2:252 blocked for more than 120 seconds.
  Workqueue: pm pm_runtime_work
  Call Trace:
   schedule+0x28/0x80
   schedule_timeout+0x1e3/0x370
   wait_for_completion+0x123/0x190
   flush_work+0x142/0x1c0
   nouveau_pmops_runtime_suspend+0x7e/0xd0 [nouveau]
   pci_pm_runtime_suspend+0x5c/0x180
   vga_switcheroo_runtime_suspend+0x1e/0xa0
   __rpm_callback+0xc1/0x200
   rpm_callback+0x1f/0x70
   rpm_suspend+0x13c/0x640
   pm_runtime_work+0x6e/0x90
   process_one_work+0x184/0x380
   worker_thread+0x2e/0x390

Bugzilla: https://bugs.archlinux.org/task/53497
Bugzilla: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=870523
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=70388#c33

index 69d6e61a01ec..6ed9cb053dfa 100644
@@ -570,9 +570,15 @@ nouveau_connector_detect(struct drm_connector *connector, bool force)
 		nv_connector->edid = NULL;
 	}
 
-	ret = pm_runtime_get_sync(connector->dev->dev);
-	if (ret < 0 && ret != -EACCES)
-		return conn_status;
+	/* Outputs are only polled while runtime active, so acquiring a
+	 * runtime PM ref here is unnecessary (and would deadlock upon
+	 * runtime suspend because it waits for polling to finish).
+	 */
+	if (!drm_kms_helper_is_poll_worker()) {
+		ret = pm_runtime_get_sync(connector->dev->dev);
+		if (ret < 0 && ret != -EACCES)
+			return conn_status;
+	}
 
 	nv_encoder = nouveau_connector_ddc_detect(connector);
 	if (nv_encoder && (i2c = nv_encoder->i2c) != NULL) {

@@ -647,8 +653,10 @@ nouveau_connector_detect(struct drm_connector *connector, bool force)
 
  out:
 
-	pm_runtime_mark_last_busy(connector->dev->dev);
-	pm_runtime_put_autosuspend(connector->dev->dev);
+	if (!drm_kms_helper_is_poll_worker()) {
+		pm_runtime_mark_last_busy(connector->dev->dev);
+		pm_runtime_put_autosuspend(connector->dev->dev);
+	}
 
 	return conn_status;
 }