[PATCH 3/5] drm/nouveau: Fix deadlock on runtime suspend

Lukas Wunner
2018-02-11T09:38:28Z

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
Fixes: 5addcf0a5f0f ("nouveau: add runtime PM support (v0.9)")
Cc: stable@vger.kernel.org # v3.12+: 1234567890ab: workqueue: Allow retrieval of current task's work struct
Cc: stable@vger.kernel.org # v3.12+: 1234567890ab: drm: Allow determining if current task is output poll worker
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
---
drivers/gpu/drm/nouveau/nouveau_connector.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_connector.c b/drivers/gpu/drm/nouveau/nouveau_connector.c
index 69d6e61a01ec..6ed9cb053dfa 100644
--- a/drivers/gpu/drm/nouveau/nouveau_connector.c
+++ b/drivers/gpu/drm/nouveau/nouveau_connector.c
@@ -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;
}
--
2.15.1