[Nouveau] [PATCH v3 3/8] drm/fb_helper: Introduce hotplug_suspend/resume()
William Lewis
minutemaidpark at hotmail.com
Tue Jul 31 14:14:15 UTC 2018
On 07/30/2018 07:39 PM, Lyude Paul wrote:
> I'm sure I don't need to tell you that fb_helper's locking is a mess.
> That being said; fb_helper's locking mess can seriously complicate the
> runtime suspend/resume operations of drivers because it can invoke
> atomic commits and connector probing from anywhere that calls
> drm_fb_helper_hotplug_event(). Since most drivers use
> drm_fb_helper_output_poll_changed() as their output_poll_changed
> handler, this can happen in every single context that can fire off a
> hotplug event. An example:
>
> [ 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] =============================================
>
> Because of this, there's an unreasonable number of places that drm
> drivers would need to insert special handling to prevent trying to
> resume the device from all of these contexts that can deadlock. It's
> difficult even to try synchronizing with fb_helper in these contexts as
> well, since any of them could introduce a deadlock by waiting to acquire
> the top-level fb_helper mutex, while it's being held by another thread
> that might potentially call down to pm_runtime_get_sync().
>
> Luckily-there's no actual reason we need to allow fb_helper to handle
> hotplugging at all when runtime suspending a device. If a hotplug
> happens during a runtime suspend operation, there's no reason the driver
> can't just re-enable fbcon's hotplug handling and bring it up to speed
> with hotplugging events it may have missed by calling
> drm_fb_helper_hotplug_event().
>
> So, let's make this easy and just add helpers to handle disabling and
> enabling fb_helper connector probing() without having to potentially
> wait on fb_helper to finish it's work. This will let us fix the runtime
> suspend/resume deadlocks that we've been experiencing with nouveau,
> along with being able to fix some of the incorrect runtime PM core
> interaction that other DRM drivers currently perform to work around
> these issues.
>
> Signed-off-by: Lyude Paul <lyude at redhat.com>
> Cc: stable at vger.kernel.org
> Cc: Lukas Wunner <lukas at wunner.de>
> Cc: Karol Herbst <karolherbst at gmail.com>
> ---
> drivers/gpu/drm/drm_fb_helper.c | 65 +++++++++++++++++++++++++++++++++
> include/drm/drm_fb_helper.h | 20 ++++++++++
> 2 files changed, 85 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 2ee1eaa66188..28d59befbc92 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -2733,6 +2733,66 @@ int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel)
> }
> EXPORT_SYMBOL(drm_fb_helper_initial_config);
>
> +/**
> + * drm_fb_helper_resume_hotplug - Allow fb_helper to handle probing new
> + * connectors again, and bring it up to date
> + * with the current device's connector status
> + * fb_helper: driver-allocated fbdev helper, can be NULL
> + *
> + * Allow fb_helper to react to connector status changes again after having
> + * been disabled through drm_fb_helper_suspend_hotplug(). This also schedules
> + * a fb_helper hotplug event to bring fb_helper up to date with the current
> + * status of the DRM device's connectors.
> + */
> +void
> +drm_fb_helper_resume_hotplug(struct drm_fb_helper *fb_helper)
> +{
> + fb_helper->hotplug_suspended = false;
> + drm_fb_helper_hotplug_event(fb_helper);
> +}
> +EXPORT_SYMBOL(drm_fb_helper_resume_hotplug);
> +
> +/**
> + * drm_fb_helper_suspend_hotplug - Attempt to temporarily inhibit fb_helper's
> + * ability to respond to connector changes
> + * without waiting
> + * @fb_helper: driver-allocated fbdev helper, can be NULL
But if it is...
> + *
> + * Temporarily prevent fb_helper from being able to handle connector changes,
> + * but only if it isn't busy doing something else. The connector probing
> + * routines in fb_helper can potentially grab any modesetting lock imaginable,
> + * which dramatically complicates the runtime suspend process. This helper can
> + * be used to simplify the process of runtime suspend by allowing the driver
> + * to disable unpredictable fb_helper operations as early as possible, without
> + * requiring that we try waiting on fb_helper (as this could lead to very
> + * difficult to solve deadlocks with runtime suspend code if fb_helper ends up
> + * needing to acquire a runtime PM reference).
> + *
> + * This call should be put at the very start of a driver's runtime suspend
> + * operation if desired. The driver must be responsible for re-enabling
> + * fb_helper hotplug handling when normal hotplug detection becomes available
> + * on the device again. This will usually happen if runtime suspend is
> + * aborted, or when the device is runtime resumed.
> + *
> + * Returns: true if hotplug handling was disabled, false if disabling hotplug
> + * handling would mean waiting on fb_helper.
> + */
> +bool
> +drm_fb_helper_suspend_hotplug(struct drm_fb_helper *fb_helper)
> +{
> + int ret;
> +
> + ret = mutex_trylock(&fb_helper->lock);
Kaboom!
> + if (!ret)
> + return false;
> +
> + fb_helper->hotplug_suspended = true;
> + mutex_unlock(&fb_helper->lock);
> +
> + return true;
> +}
> +EXPORT_SYMBOL(drm_fb_helper_suspend_hotplug);
> +
> /**
> * drm_fb_helper_hotplug_event - respond to a hotplug notification by
> * probing all the outputs attached to the fb
> @@ -2774,6 +2834,11 @@ int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
> return err;
> }
>
> + if (fb_helper->hotplug_suspended) {
> + mutex_unlock(&fb_helper->lock);
> + return err;
> + }
> +
> DRM_DEBUG_KMS("\n");
>
> drm_setup_crtcs(fb_helper, fb_helper->fb->width, fb_helper->fb->height);
> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> index b069433e7fc1..30881131075c 100644
> --- a/include/drm/drm_fb_helper.h
> +++ b/include/drm/drm_fb_helper.h
> @@ -232,6 +232,14 @@ struct drm_fb_helper {
> * See also: @deferred_setup
> */
> int preferred_bpp;
> +
> + /**
> + * @hotplug_suspended:
> + *
> + * Whether or not we can currently handle hotplug events, or if we
> + * need to wait for the DRM device to uninhibit us.
> + */
> + bool hotplug_suspended;
> };
>
> /**
> @@ -330,6 +338,10 @@ void drm_fb_helper_fbdev_teardown(struct drm_device *dev);
>
> void drm_fb_helper_lastclose(struct drm_device *dev);
> void drm_fb_helper_output_poll_changed(struct drm_device *dev);
> +
> +void drm_fb_helper_resume_hotplug(struct drm_fb_helper *fb_helper);
> +bool drm_fb_helper_suspend_hotplug(struct drm_fb_helper *fb_helper);
> +
> #else
> static inline void drm_fb_helper_prepare(struct drm_device *dev,
> struct drm_fb_helper *helper,
> @@ -564,6 +576,14 @@ static inline void drm_fb_helper_output_poll_changed(struct drm_device *dev)
> {
> }
>
> +static inline void
> +drm_fb_helper_resume_hotplug(struct drm_fb_helper *fb_helper)
> +{
> +}
> +static inline bool
> +drm_fb_helper_suspend_hotplug(struct drm_fb_helper *fb_helper)
> +{
> +}
> #endif
>
> static inline int
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