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SubjectRe: [PATCH 2/2] drm/nouveau: Handle fbcon suspend/resume in seperate worker
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Hi,

Good catch (both the previous patch as well as this one).
I've one small comment inline:

On 12-01-17 03:25, Lyude wrote:
> Resuming from RPM can happen while already holding
> dev->mode_config.mutex. This means we can't actually handle fbcon in
> any RPM resume workers, since restoring fbcon requires grabbing
> dev->mode_config.mutex again. So move the fbcon suspend/resume code into
> it's own worker, and rely on that instead to avoid deadlocking.
>
> This fixes more deadlocks for runtime suspending the GPU on the ThinkPad
> W541. Reproduction recipe:
>
> - Get a machine with both optimus and a nvidia card with connectors
> attached to it
> - Wait for the nvidia GPU to suspend
> - Attempt to manually reprobe any of the connectors on the nvidia GPU
> using sysfs
> - *deadlock*
>
> Signed-off-by: Lyude <lyude@redhat.com>
> Cc: Hans de Goede <hdegoede@redhat.com>
> Cc: Kilian Singer <kilian.singer@quantumtechnology.info>
> Cc: Lukas Wunner <lukas@wunner.de>
> Cc: David Airlie <airlied@redhat.com>
> ---
> drivers/gpu/drm/nouveau/nouveau_drv.h | 2 ++
> drivers/gpu/drm/nouveau/nouveau_fbcon.c | 43 ++++++++++++++++++++++++++-------
> 2 files changed, 36 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_drv.h b/drivers/gpu/drm/nouveau/nouveau_drv.h
> index 8d5ed5b..42c1fa5 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_drv.h
> +++ b/drivers/gpu/drm/nouveau/nouveau_drv.h
> @@ -165,6 +165,8 @@ struct nouveau_drm {
> struct backlight_device *backlight;
> struct list_head bl_connectors;
> struct work_struct hpd_work;
> + struct work_struct fbcon_work;
> + int fbcon_new_state;
> #ifdef CONFIG_ACPI
> struct notifier_block acpi_nb;
> #endif
> diff --git a/drivers/gpu/drm/nouveau/nouveau_fbcon.c b/drivers/gpu/drm/nouveau/nouveau_fbcon.c
> index 2f2a3dc..87cd30b 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_fbcon.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_fbcon.c
> @@ -470,19 +470,43 @@ static const struct drm_fb_helper_funcs nouveau_fbcon_helper_funcs = {
> .fb_probe = nouveau_fbcon_create,
> };
>
> +static void
> +nouveau_fbcon_set_suspend_work(struct work_struct *work)
> +{
> + struct nouveau_drm *drm = container_of(work, typeof(*drm), fbcon_work);
> + int state = drm->fbcon_new_state;

The compiler may decide to optimize away this variable
and simply use drm->fbcon_new_state in the if-s below,
which is racy. I would fix this by making
drm->fbcon_new_state an atomic_t and using

atomic_read(&drm->fbcon_new_state) here.
(and atomic_set below).

Regards,

Hans



> +
> + if (state == FBINFO_STATE_RUNNING)
> + pm_runtime_get_sync(drm->dev->dev);
> +
> + console_lock();
> + if (state == FBINFO_STATE_RUNNING)
> + nouveau_fbcon_accel_restore(drm->dev);
> + drm_fb_helper_set_suspend(&drm->fbcon->helper, state);
> + if (state != FBINFO_STATE_RUNNING)
> + nouveau_fbcon_accel_save_disable(drm->dev);
> + console_unlock();
> +
> + if (state == FBINFO_STATE_RUNNING) {
> + pm_runtime_mark_last_busy(drm->dev->dev);
> + pm_runtime_put_sync(drm->dev->dev);
> + }
> +}
> +
> void
> nouveau_fbcon_set_suspend(struct drm_device *dev, int state)
> {
> 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 (state != FBINFO_STATE_RUNNING)
> - nouveau_fbcon_accel_save_disable(dev);
> - console_unlock();
> - }
> +
> + if (!drm->fbcon)
> + return;
> +
> + drm->fbcon_new_state = state;
> + /* Since runtime resume can happen as a result of a sysfs operation,
> + * it's possible we already have the console locked. So handle fbcon
> + * init/deinit from a seperate work thread
> + */
> + schedule_work(&drm->fbcon_work);
> }
>
> int
> @@ -502,6 +526,7 @@ nouveau_fbcon_init(struct drm_device *dev)
> return -ENOMEM;
>
> drm->fbcon = fbcon;
> + INIT_WORK(&drm->fbcon_work, nouveau_fbcon_set_suspend_work);
>
> drm_fb_helper_prepare(dev, &fbcon->helper, &nouveau_fbcon_helper_funcs);
>
>

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