Re: [PATCH v2] drm/i915: Break modeset deadlocks on reset

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Op 21-06-17 om 16:24 schreef Chris Wilson:
> Trying to do a modeset from within a reset is fraught with danger. We
> can fall into a cyclic deadlock where the modeset is waiting on a
> previous modeset that is waiting on a request, and since the GPU hung
> that request completion is waiting on the reset. As modesetting doesn't
> allow its locks to be broken and restarted, or for its *own* reset
> mechanism to take over the display, we have to do something very
> evil instead. If we detect that we are stuck waiting to prepare the
> display reset (by using a very simple timeout), resort to cancelling all
> in-flight requests and throwing the user data into /dev/null, which is
> marginally better than the driver locking up and keeping that data to
> itself.
>
> This is not a fix; this is just a workaround that unbreaks machines
> until we can resolve the deadlock in a way that doesn't lose data!
>
> v2: Move the retirement from set-wegded to the i915_reset() error path,
> after which we no longer any delayed worker cleanup for
> i915_handle_error()
> v3: C abuse for syntactic sugar
>
> References: https://bugs.freedesktop.org/show_bug.cgi?id=99093
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Mika Kuoppala <mika.kuoppala@intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.c |  1 +
>  drivers/gpu/drm/i915/i915_gem.c | 18 ++++-------------
>  drivers/gpu/drm/i915/i915_irq.c | 45 ++++++++++++++++++++++++++++++++++++++++-
>  3 files changed, 49 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index d1aa10c9cc5d..1df957b986c7 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -1914,6 +1914,7 @@ void i915_reset(struct drm_i915_private *dev_priv)
>  
>  error:
>  	i915_gem_set_wedged(dev_priv);
> +	i915_gem_retire_requests(dev_priv);
>  	goto finish;
>  }
>  
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index ae3ce1314bd1..36d838677982 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3062,7 +3062,8 @@ static void engine_set_wedged(struct intel_engine_cs *engine)
>  	/* Mark all executing requests as skipped */
>  	spin_lock_irqsave(&engine->timeline->lock, flags);
>  	list_for_each_entry(request, &engine->timeline->requests, link)
> -		dma_fence_set_error(&request->fence, -EIO);
> +		if (!i915_gem_request_completed(request))
> +			dma_fence_set_error(&request->fence, -EIO);
>  	spin_unlock_irqrestore(&engine->timeline->lock, flags);
>  
>  	/* Mark all pending requests as complete so that any concurrent
> @@ -3108,6 +3109,7 @@ static int __i915_gem_set_wedged_BKL(void *data)
>  	struct intel_engine_cs *engine;
>  	enum intel_engine_id id;
>  
> +	set_bit(I915_WEDGED, &i915->gpu_error.flags);
>  	for_each_engine(engine, i915, id)
>  		engine_set_wedged(engine);
>  
> @@ -3116,20 +3118,7 @@ static int __i915_gem_set_wedged_BKL(void *data)
>  
>  void i915_gem_set_wedged(struct drm_i915_private *dev_priv)
>  {
> -	lockdep_assert_held(&dev_priv->drm.struct_mutex);
> -	set_bit(I915_WEDGED, &dev_priv->gpu_error.flags);
> -
> -	/* Retire completed requests first so the list of inflight/incomplete
> -	 * requests is accurate and we don't try and mark successful requests
> -	 * as in error during __i915_gem_set_wedged_BKL().
> -	 */
> -	i915_gem_retire_requests(dev_priv);
> -
>  	stop_machine(__i915_gem_set_wedged_BKL, dev_priv, NULL);
> -
> -	i915_gem_contexts_lost(dev_priv);
> -
> -	mod_delayed_work(dev_priv->wq, &dev_priv->gt.idle_work, 0);
>  }
>  
>  bool i915_gem_unset_wedged(struct drm_i915_private *i915)
> @@ -3184,6 +3173,7 @@ bool i915_gem_unset_wedged(struct drm_i915_private *i915)
>  	 * context and do not require stop_machine().
>  	 */
>  	intel_engines_reset_default_submission(i915);
> +	i915_gem_contexts_lost(i915);
>  
>  	smp_mb__before_atomic(); /* complete takeover before enabling execbuf */
>  	clear_bit(I915_WEDGED, &i915->gpu_error.flags);
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index b1c7d1a04612..c948a5bd031c 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -2599,6 +2599,46 @@ static irqreturn_t gen8_irq_handler(int irq, void *arg)
>  	return ret;
>  }
>  
> +struct wedge_me {
> +	struct delayed_work work;
> +	struct drm_i915_private *i915;
> +	const char *name;
> +};
> +
> +static void wedge_me(struct work_struct *work)
> +{
> +	struct wedge_me *w = container_of(work, typeof(*w), work.work);
> +
> +	dev_err(w->i915->drm.dev,
> +		"%s timed out, cancelling all in-flight rendering.\n",
> +		w->name);
> +	i915_gem_set_wedged(w->i915);
> +}
> +
> +static void __init_wedge(struct wedge_me *w,
> +			 struct drm_i915_private *i915,
> +			 long timeout,
> +			 const char *name)
> +{
> +	w->i915 = i915;
> +	w->name = name;
> +
> +	INIT_DELAYED_WORK_ONSTACK(&w->work, wedge_me);
> +	schedule_delayed_work(&w->work, timeout);
> +}
> +
> +static void __fini_wedge(struct wedge_me *w)
> +{
> +	cancel_delayed_work_sync(&w->work);
> +	destroy_delayed_work_on_stack(&w->work);
> +	w->i915 = NULL;
> +}
> +
> +#define i915_wedge_on_timeout(W, DEV, TIMEOUT, MSG)			\
> +	for (__init_wedge((W), (DEV), (TIMEOUT), (MSG));		\
> +	     (W)->i915;							\
> +	     __fini_wedge((W)))
> +
>  /**
>   * i915_reset_device - do process context error handling work
>   * @dev_priv: i915 device private
> @@ -2612,13 +2652,16 @@ static void i915_reset_device(struct drm_i915_private *dev_priv)
>  	char *error_event[] = { I915_ERROR_UEVENT "=1", NULL };
>  	char *reset_event[] = { I915_RESET_UEVENT "=1", NULL };
>  	char *reset_done_event[] = { I915_ERROR_UEVENT "=0", NULL };
> +	struct wedge_me w;
>  
>  	kobject_uevent_env(kobj, KOBJ_CHANGE, error_event);
>  
>  	DRM_DEBUG_DRIVER("resetting chip\n");
>  	kobject_uevent_env(kobj, KOBJ_CHANGE, reset_event);
>  
> -	intel_prepare_reset(dev_priv);
> +	i915_wedge_on_timeout(&w, dev_priv, HZ, "intel_prepare_reset") {
> +		intel_prepare_reset(dev_priv);
> +	}
I think v2 was more clear here.

But if this is just for the modeset locks, why not add a timeout to i915_sw_fence_await_reservation on old_obj?

That would allow us to end the deadlocks without having to kill off all fences first.
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