[PATCH 4.18 68/88] drm/nouveau/drm/nouveau: Fix deadlock with fb_helper with async RPM requests

From: Greg Kroah-Hartman
Date: Thu Sep 27 2018 - 05:16:10 EST

4.18-stable review patch. If anyone has any objections, please let me know.

------------------

From: Lyude Paul <lyude@xxxxxxxxxx>

commit 7fec8f5379fb6eddabc0aaef6d2304c366808f97 upstream.

Currently, nouveau uses the generic drm_fb_helper_output_poll_changed()
function provided by DRM as it's output_poll_changed callback.
Unfortunately however, this function doesn't grab runtime PM references
early enough and even if it did-we can't block waiting for the device to
resume in output_poll_changed() since it's very likely that we'll need
to grab the fb_helper lock at some point during the runtime resume
process. This currently results in deadlocking like so:

[ 246.669625] INFO: task kworker/4:0:37 blocked for more than 120 seconds.
[ 246.673398] Not tainted 4.18.0-rc5Lyude-Test+ #2
[ 246.675271] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 246.676527] kworker/4:0 D 0 37 2 0x80000000
[ 246.677580] Workqueue: events output_poll_execute [drm_kms_helper]
[ 246.678704] Call Trace:
[ 246.679753] __schedule+0x322/0xaf0
[ 246.680916] schedule+0x33/0x90
[ 246.681924] schedule_preempt_disabled+0x15/0x20
[ 246.683023] __mutex_lock+0x569/0x9a0
[ 246.684035] ? kobject_uevent_env+0x117/0x7b0
[ 246.685132] ? drm_fb_helper_hotplug_event.part.28+0x20/0xb0 [drm_kms_helper]
[ 246.686179] mutex_lock_nested+0x1b/0x20
[ 246.687278] ? mutex_lock_nested+0x1b/0x20
[ 246.688307] drm_fb_helper_hotplug_event.part.28+0x20/0xb0 [drm_kms_helper]
[ 246.689420] drm_fb_helper_output_poll_changed+0x23/0x30 [drm_kms_helper]
[ 246.690462] drm_kms_helper_hotplug_event+0x2a/0x30 [drm_kms_helper]
[ 246.691570] output_poll_execute+0x198/0x1c0 [drm_kms_helper]
[ 246.692611] process_one_work+0x231/0x620
[ 246.693725] worker_thread+0x214/0x3a0
[ 246.694756] kthread+0x12b/0x150
[ 246.695856] ? wq_pool_ids_show+0x140/0x140
[ 246.696888] ? kthread_create_worker_on_cpu+0x70/0x70
[ 246.697998] ret_from_fork+0x3a/0x50
[ 246.699034] INFO: task kworker/0:1:60 blocked for more than 120 seconds.
[ 246.700153] Not tainted 4.18.0-rc5Lyude-Test+ #2
[ 246.701182] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 246.702278] kworker/0:1 D 0 60 2 0x80000000
[ 246.703293] Workqueue: pm pm_runtime_work
[ 246.704393] Call Trace:
[ 246.705403] __schedule+0x322/0xaf0
[ 246.706439] ? wait_for_completion+0x104/0x190
[ 246.707393] schedule+0x33/0x90
[ 246.708375] schedule_timeout+0x3a5/0x590
[ 246.709289] ? mark_held_locks+0x58/0x80
[ 246.710208] ? _raw_spin_unlock_irq+0x2c/0x40
[ 246.711222] ? wait_for_completion+0x104/0x190
[ 246.712134] ? trace_hardirqs_on_caller+0xf4/0x190
[ 246.713094] ? wait_for_completion+0x104/0x190
[ 246.713964] wait_for_completion+0x12c/0x190
[ 246.714895] ? wake_up_q+0x80/0x80
[ 246.715727] ? get_work_pool+0x90/0x90
[ 246.716649] flush_work+0x1c9/0x280
[ 246.717483] ? flush_workqueue_prep_pwqs+0x1b0/0x1b0
[ 246.718442] __cancel_work_timer+0x146/0x1d0
[ 246.719247] cancel_delayed_work_sync+0x13/0x20
[ 246.720043] drm_kms_helper_poll_disable+0x1f/0x30 [drm_kms_helper]
[ 246.721123] nouveau_pmops_runtime_suspend+0x3d/0xb0 [nouveau]
[ 246.721897] pci_pm_runtime_suspend+0x6b/0x190
[ 246.722825] ? pci_has_legacy_pm_support+0x70/0x70
[ 246.723737] __rpm_callback+0x7a/0x1d0
[ 246.724721] ? pci_has_legacy_pm_support+0x70/0x70
[ 246.725607] rpm_callback+0x24/0x80
[ 246.726553] ? pci_has_legacy_pm_support+0x70/0x70
[ 246.727376] rpm_suspend+0x142/0x6b0
[ 246.728185] pm_runtime_work+0x97/0xc0
[ 246.728938] process_one_work+0x231/0x620
[ 246.729796] worker_thread+0x44/0x3a0
[ 246.730614] kthread+0x12b/0x150
[ 246.731395] ? wq_pool_ids_show+0x140/0x140
[ 246.732202] ? kthread_create_worker_on_cpu+0x70/0x70
[ 246.732878] ret_from_fork+0x3a/0x50
[ 246.733768] INFO: task kworker/4:2:422 blocked for more than 120 seconds.
[ 246.734587] Not tainted 4.18.0-rc5Lyude-Test+ #2
[ 246.735393] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 246.736113] kworker/4:2 D 0 422 2 0x80000080
[ 246.736789] Workqueue: events_long drm_dp_mst_link_probe_work [drm_kms_helper]
[ 246.737665] Call Trace:
[ 246.738490] __schedule+0x322/0xaf0
[ 246.739250] schedule+0x33/0x90
[ 246.739908] rpm_resume+0x19c/0x850
[ 246.740750] ? finish_wait+0x90/0x90
[ 246.741541] __pm_runtime_resume+0x4e/0x90
[ 246.742370] nv50_disp_atomic_commit+0x31/0x210 [nouveau]
[ 246.743124] drm_atomic_commit+0x4a/0x50 [drm]
[ 246.743775] restore_fbdev_mode_atomic+0x1c8/0x240 [drm_kms_helper]
[ 246.744603] restore_fbdev_mode+0x31/0x140 [drm_kms_helper]
[ 246.745373] drm_fb_helper_restore_fbdev_mode_unlocked+0x54/0xb0 [drm_kms_helper]
[ 246.746220] drm_fb_helper_set_par+0x2d/0x50 [drm_kms_helper]
[ 246.746884] drm_fb_helper_hotplug_event.part.28+0x96/0xb0 [drm_kms_helper]
[ 246.747675] drm_fb_helper_output_poll_changed+0x23/0x30 [drm_kms_helper]
[ 246.748544] drm_kms_helper_hotplug_event+0x2a/0x30 [drm_kms_helper]
[ 246.749439] nv50_mstm_hotplug+0x15/0x20 [nouveau]
[ 246.750111] drm_dp_send_link_address+0x177/0x1c0 [drm_kms_helper]
[ 246.750764] drm_dp_check_and_send_link_address+0xa8/0xd0 [drm_kms_helper]
[ 246.751602] drm_dp_mst_link_probe_work+0x51/0x90 [drm_kms_helper]
[ 246.752314] process_one_work+0x231/0x620
[ 246.752979] worker_thread+0x44/0x3a0
[ 246.753838] kthread+0x12b/0x150
[ 246.754619] ? wq_pool_ids_show+0x140/0x140
[ 246.755386] ? kthread_create_worker_on_cpu+0x70/0x70
[ 246.756162] ret_from_fork+0x3a/0x50
[ 246.756847]
Showing all locks held in the system:
[ 246.758261] 3 locks held by kworker/4:0/37:
[ 246.759016] #0: 00000000f8df4d2d ((wq_completion)"events"){+.+.}, at: process_one_work+0x1b3/0x620
[ 246.759856] #1: 00000000e6065461 ((work_completion)(&(&dev->mode_config.output_poll_work)->work)){+.+.}, at: process_one_work+0x1b3/0x620
[ 246.760670] #2: 00000000cb66735f (&helper->lock){+.+.}, at: drm_fb_helper_hotplug_event.part.28+0x20/0xb0 [drm_kms_helper]
[ 246.761516] 2 locks held by kworker/0:1/60:
[ 246.762274] #0: 00000000fff6be0f ((wq_completion)"pm"){+.+.}, at: process_one_work+0x1b3/0x620
[ 246.762982] #1: 000000005ab44fb4 ((work_completion)(&dev->power.work)){+.+.}, at: process_one_work+0x1b3/0x620
[ 246.763890] 1 lock held by khungtaskd/64:
[ 246.764664] #0: 000000008cb8b5c3 (rcu_read_lock){....}, at: debug_show_all_locks+0x23/0x185
[ 246.765588] 5 locks held by kworker/4:2/422:
[ 246.766440] #0: 00000000232f0959 ((wq_completion)"events_long"){+.+.}, at: process_one_work+0x1b3/0x620
[ 246.767390] #1: 00000000bb59b134 ((work_completion)(&mgr->work)){+.+.}, at: process_one_work+0x1b3/0x620
[ 246.768154] #2: 00000000cb66735f (&helper->lock){+.+.}, at: drm_fb_helper_restore_fbdev_mode_unlocked+0x4c/0xb0 [drm_kms_helper]
[ 246.768966] #3: 000000004c8f0b6b (crtc_ww_class_acquire){+.+.}, at: restore_fbdev_mode_atomic+0x4b/0x240 [drm_kms_helper]
[ 246.769921] #4: 000000004c34a296 (crtc_ww_class_mutex){+.+.}, at: drm_modeset_backoff+0x8a/0x1b0 [drm]
[ 246.770839] 1 lock held by dmesg/1038:
[ 246.771739] 2 locks held by zsh/1172:
[ 246.772650] #0: 00000000836d0438 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40
[ 246.773680] #1: 000000001f4f4d48 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0xc1/0x870

[ 246.775522] =============================================

After trying dozens of different solutions, I found one very simple one
that should also have the benefit of preventing us from having to fight
locking for the rest of our lives. So, we work around these deadlocks by
deferring all fbcon hotplug events that happen after the runtime suspend
process starts until after the device is resumed again.

Changes since v7:
- Fixup commit message - Daniel Vetter

Changes since v6:
- Remove unused nouveau_fbcon_hotplugged_in_suspend() - Ilia

Changes since v5:
- Come up with the (hopefully final) solution for solving this dumb
problem, one that is a lot less likely to cause issues with locking in
the future. This should work around all deadlock conditions with fbcon
brought up thus far.

Changes since v4:
- Add nouveau_fbcon_hotplugged_in_suspend() to workaround deadlock
condition that Lukas described
- Just move all of this out of drm_fb_helper. It seems that other DRM
drivers have already figured out other workarounds for this. If other
drivers do end up needing this in the future, we can just move this
back into drm_fb_helper again.

Changes since v3:
- Actually check if fb_helper is NULL in both new helpers
- Actually check drm_fbdev_emulation in both new helpers
- Don't fire off a fb_helper hotplug unconditionally; only do it if
the following conditions are true (as otherwise, calling this in the
wrong spot will cause Bad Things to happen):
- fb_helper hotplug handling was actually inhibited previously
- fb_helper actually has a delayed hotplug pending
- fb_helper is actually bound
- fb_helper is actually initialized
- Add __must_check to drm_fb_helper_suspend_hotplug(). There's no
situation where a driver would actually want to use this without
checking the return value, so enforce that
- Rewrite and clarify the documentation for both helpers.
- Make sure to return true in the drm_fb_helper_suspend_hotplug() stub
that's provided in drm_fb_helper.h when CONFIG_DRM_FBDEV_EMULATION
isn't enabled
- Actually grab the toplevel fb_helper lock in
drm_fb_helper_resume_hotplug(), since it's possible other activity
(such as a hotplug) could be going on at the same time the driver
calls drm_fb_helper_resume_hotplug(). We need this to check whether or
not drm_fb_helper_hotplug_event() needs to be called anyway

Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
Reviewed-by: Karol Herbst <kherbst@xxxxxxxxxx>
Acked-by: Daniel Vetter <daniel@xxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: Lukas Wunner <lukas@xxxxxxxxx>
Signed-off-by: Ben Skeggs <bskeggs@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
drivers/gpu/drm/nouveau/dispnv50/disp.c | 2 -
drivers/gpu/drm/nouveau/nouveau_display.c | 2 -
drivers/gpu/drm/nouveau/nouveau_fbcon.c | 57 ++++++++++++++++++++++++++++++
drivers/gpu/drm/nouveau/nouveau_fbcon.h | 5 ++
4 files changed, 64 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -2080,7 +2080,7 @@ nv50_disp_atomic_state_alloc(struct drm_
static const struct drm_mode_config_funcs
nv50_disp_func = {
.fb_create = nouveau_user_framebuffer_create,
- .output_poll_changed = drm_fb_helper_output_poll_changed,
+ .output_poll_changed = nouveau_fbcon_output_poll_changed,
.atomic_check = nv50_disp_atomic_check,
.atomic_commit = nv50_disp_atomic_commit,
.atomic_state_alloc = nv50_disp_atomic_state_alloc,
--- a/drivers/gpu/drm/nouveau/nouveau_display.c
+++ b/drivers/gpu/drm/nouveau/nouveau_display.c
@@ -293,7 +293,7 @@ nouveau_user_framebuffer_create(struct d

static const struct drm_mode_config_funcs nouveau_mode_config_funcs = {
.fb_create = nouveau_user_framebuffer_create,
- .output_poll_changed = drm_fb_helper_output_poll_changed,
+ .output_poll_changed = nouveau_fbcon_output_poll_changed,
};


--- a/drivers/gpu/drm/nouveau/nouveau_fbcon.c
+++ b/drivers/gpu/drm/nouveau/nouveau_fbcon.c
@@ -466,6 +466,7 @@ nouveau_fbcon_set_suspend_work(struct wo
console_unlock();

if (state == FBINFO_STATE_RUNNING) {
+ nouveau_fbcon_hotplug_resume(drm->fbcon);
pm_runtime_mark_last_busy(drm->dev->dev);
pm_runtime_put_sync(drm->dev->dev);
}
@@ -487,6 +488,61 @@ nouveau_fbcon_set_suspend(struct drm_dev
schedule_work(&drm->fbcon_work);
}

+void
+nouveau_fbcon_output_poll_changed(struct drm_device *dev)
+{
+ struct nouveau_drm *drm = nouveau_drm(dev);
+ struct nouveau_fbdev *fbcon = drm->fbcon;
+ int ret;
+
+ if (!fbcon)
+ return;
+
+ mutex_lock(&fbcon->hotplug_lock);
+
+ ret = pm_runtime_get(dev->dev);
+ if (ret == 1 || ret == -EACCES) {
+ drm_fb_helper_hotplug_event(&fbcon->helper);
+
+ pm_runtime_mark_last_busy(dev->dev);
+ pm_runtime_put_autosuspend(dev->dev);
+ } else if (ret == 0) {
+ /* If the GPU was already in the process of suspending before
+ * this event happened, then we can't block here as we'll
+ * deadlock the runtime pmops since they wait for us to
+ * finish. So, just defer this event for when we runtime
+ * resume again. It will be handled by fbcon_work.
+ */
+ NV_DEBUG(drm, "fbcon HPD event deferred until runtime resume\n");
+ fbcon->hotplug_waiting = true;
+ pm_runtime_put_noidle(drm->dev->dev);
+ } else {
+ DRM_WARN("fbcon HPD event lost due to RPM failure: %d\n",
+ ret);
+ }
+
+ mutex_unlock(&fbcon->hotplug_lock);
+}
+
+void
+nouveau_fbcon_hotplug_resume(struct nouveau_fbdev *fbcon)
+{
+ struct nouveau_drm *drm;
+
+ if (!fbcon)
+ return;
+ drm = nouveau_drm(fbcon->helper.dev);
+
+ mutex_lock(&fbcon->hotplug_lock);
+ if (fbcon->hotplug_waiting) {
+ fbcon->hotplug_waiting = false;
+
+ NV_DEBUG(drm, "Handling deferred fbcon HPD events\n");
+ drm_fb_helper_hotplug_event(&fbcon->helper);
+ }
+ mutex_unlock(&fbcon->hotplug_lock);
+}
+
int
nouveau_fbcon_init(struct drm_device *dev)
{
@@ -505,6 +561,7 @@ nouveau_fbcon_init(struct drm_device *de

drm->fbcon = fbcon;
INIT_WORK(&drm->fbcon_work, nouveau_fbcon_set_suspend_work);
+ mutex_init(&fbcon->hotplug_lock);

drm_fb_helper_prepare(dev, &fbcon->helper, &nouveau_fbcon_helper_funcs);

--- a/drivers/gpu/drm/nouveau/nouveau_fbcon.h
+++ b/drivers/gpu/drm/nouveau/nouveau_fbcon.h
@@ -41,6 +41,9 @@ struct nouveau_fbdev {
struct nvif_object gdi;
struct nvif_object blit;
struct nvif_object twod;
+
+ struct mutex hotplug_lock;
+ bool hotplug_waiting;
};

void nouveau_fbcon_restore(void);
@@ -68,6 +71,8 @@ void nouveau_fbcon_set_suspend(struct dr
void nouveau_fbcon_accel_save_disable(struct drm_device *dev);
void nouveau_fbcon_accel_restore(struct drm_device *dev);

+void nouveau_fbcon_output_poll_changed(struct drm_device *dev);
+void nouveau_fbcon_hotplug_resume(struct nouveau_fbdev *fbcon);
extern int nouveau_nofbaccel;

#endif /* __NV50_FBCON_H__ */