[PATCH 1/3] drm/i915: Guard pages being reaped by OOM whilst binding-to-GTT

[PATCH 1/3] drm/i915: Guard pages being reaped by OOM whilst binding-to-GTT

[Chris Wilson]

In the circumstances that the shrinker is allowed to steal the mutex
in order to reap pages, we need to be careful to prevent it operating on
the current object and shooting ourselves in the foot.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index cdcf19d..9553b40 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2922,6 +2922,8 @@ i915_gem_object_bind_to_gtt(struct drm_i915_gem_object *obj,
 	if (ret)
 		return ret;
 
+	i915_gem_object_pin_pages(obj);
+
  search_free:
 	if (map_and_fenceable)
 		free_space =
@@ -2952,14 +2954,17 @@ i915_gem_object_bind_to_gtt(struct drm_i915_gem_object *obj,
 					       obj->cache_level,
 					       map_and_fenceable,
 					       nonblocking);
-		if (ret)
+		if (ret) {
+			i915_gem_object_unpin_pages(obj);
 			return ret;
+		}
 
 		goto search_free;
 	}
 	if (WARN_ON(!i915_gem_valid_gtt_space(dev,
 					      obj->gtt_space,
 					      obj->cache_level))) {
+		i915_gem_object_unpin_pages(obj);
 		drm_mm_put_block(obj->gtt_space);
 		obj->gtt_space = NULL;
 		return -EINVAL;
@@ -2968,6 +2973,7 @@ i915_gem_object_bind_to_gtt(struct drm_i915_gem_object *obj,
 
 	ret = i915_gem_gtt_prepare_object(obj);
 	if (ret) {
+		i915_gem_object_unpin_pages(obj);
 		drm_mm_put_block(obj->gtt_space);
 		obj->gtt_space = NULL;
 		return ret;
@@ -2990,6 +2996,7 @@ i915_gem_object_bind_to_gtt(struct drm_i915_gem_object *obj,
 
 	obj->map_and_fenceable = mappable && fenceable;
 
+	i915_gem_object_unpin_pages(obj);
 	trace_i915_gem_object_bind(obj, map_and_fenceable);
 	i915_gem_verify_gtt(dev);
 	return 0;
-- 
1.7.10.4

[PATCH 2/3] drm/i915: Pin the object whilst faulting it in

[Chris Wilson]

In order to prevent reaping of the object whilst setting it up to
handle the pagefault, we need to mark it as pinned. This has the nice
side-effect of eliminating some special cases from the pagefault handler
as well!

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c |   29 +++++++++--------------------
 1 file changed, 9 insertions(+), 20 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 9553b40..a7067e0 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1345,30 +1345,17 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 	trace_i915_gem_object_fault(obj, page_offset, true, write);
 
 	/* Now bind it into the GTT if needed */
-	if (!obj->map_and_fenceable) {
-		ret = i915_gem_object_unbind(obj);
-		if (ret)
-			goto unlock;
-	}
-	if (!obj->gtt_space) {
-		ret = i915_gem_object_bind_to_gtt(obj, 0, true, false);
-		if (ret)
-			goto unlock;
-
-		ret = i915_gem_object_set_to_gtt_domain(obj, write);
-		if (ret)
-			goto unlock;
-	}
+	ret = i915_gem_object_pin(obj, 0, true, false);
+	if (ret)
+		goto unlock;
 
-	if (!obj->has_global_gtt_mapping)
-		i915_gem_gtt_bind_object(obj, obj->cache_level);
+	ret = i915_gem_object_set_to_gtt_domain(obj, write);
+	if (ret)
+		goto unpin;
 
 	ret = i915_gem_object_get_fence(obj);
 	if (ret)
-		goto unlock;
-
-	if (i915_gem_object_is_inactive(obj))
-		list_move_tail(&obj->mm_list, &dev_priv->mm.inactive_list);
+		goto unpin;
 
 	obj->fault_mappable = true;
 
@@ -1377,6 +1364,8 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 
 	/* Finally, remap it using the new GTT offset */
 	ret = vm_insert_pfn(vma, (unsigned long)vmf->virtual_address, pfn);
+unpin:
+	i915_gem_object_unpin(obj);
 unlock:
 	mutex_unlock(&dev->struct_mutex);
 out:
-- 
1.7.10.4

[PATCH 3/3] drm/i915: Borrow our struct_mutex for the direct reclaim

[Chris Wilson]

If we have hit oom whilst holding our struct_mutex, then currently we
cannot reap our own GPU buffers which likely pin most of memory, making
an outright OOM more likely. So if we are running in direct reclaim and
already hold the mutex, attempt to free buffers knowing that the
original function can not continue until we return.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c |   24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index a7067e0..38d8fa3 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4340,6 +4340,18 @@ void i915_gem_release(struct drm_device *dev, struct drm_file *file)
 	spin_unlock(&file_priv->mm.lock);
 }
 
+static bool mutex_is_locked_by(struct mutex *mutex, struct task_struct *task)
+{
+	if (!mutex_is_locked(mutex))
+		return false;
+
+#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_MUTEXES)
+	return mutex->owner == task;
+#else
+	return true;
+#endif
+}
+
 static int
 i915_gem_inactive_shrink(struct shrinker *shrinker, struct shrink_control *sc)
 {
@@ -4350,10 +4362,15 @@ i915_gem_inactive_shrink(struct shrinker *shrinker, struct shrink_control *sc)
 	struct drm_device *dev = dev_priv->dev;
 	struct drm_i915_gem_object *obj;
 	int nr_to_scan = sc->nr_to_scan;
+	bool unlock = true;
 	int cnt;
 
-	if (!mutex_trylock(&dev->struct_mutex))
-		return 0;
+	if (!mutex_trylock(&dev->struct_mutex)) {
+		if (!mutex_is_locked_by(&dev->struct_mutex, current))
+			return 0;
+
+		unlock = false;
+	}
 
 	if (nr_to_scan) {
 		nr_to_scan -= i915_gem_purge(dev_priv, nr_to_scan);
@@ -4369,6 +4386,7 @@ i915_gem_inactive_shrink(struct shrinker *shrinker, struct shrink_control *sc)
 		if (obj->pin_count == 0 && obj->pages_pin_count == 0)
 			cnt += obj->base.size >> PAGE_SHIFT;
 
-	mutex_unlock(&dev->struct_mutex);
+	if (unlock)
+		mutex_unlock(&dev->struct_mutex);
 	return cnt;
 }
-- 
1.7.10.4

Re: [PATCH 3/3] drm/i915: Borrow our struct_mutex for the direct reclaim

[Daniel Vetter]

On Tue, Nov 20, 2012 at 10:45:18AM +0000, Chris Wilson wrote:
> If we have hit oom whilst holding our struct_mutex, then currently we
> cannot reap our own GPU buffers which likely pin most of memory, making
> an outright OOM more likely. So if we are running in direct reclaim and
> already hold the mutex, attempt to free buffers knowing that the
> original function can not continue until we return.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

Ok, I've merged the two prep patches, but I think this one here will blow
up, see below.

> ---
>  drivers/gpu/drm/i915/i915_gem.c |   24 +++++++++++++++++++++---
>  1 file changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index a7067e0..38d8fa3 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -4340,6 +4340,18 @@ void i915_gem_release(struct drm_device *dev, struct drm_file *file)
>  	spin_unlock(&file_priv->mm.lock);
>  }
>  
> +static bool mutex_is_locked_by(struct mutex *mutex, struct task_struct *task)
> +{
> +	if (!mutex_is_locked(mutex))
> +		return false;
> +
> +#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_MUTEXES)
> +	return mutex->owner == task;
> +#else
> +	return true;

I guess the idea is that on UP we can steal the lock, but that will
introduce tons of new places where the backing storage can disappear
(everywhere we block, instead of just allocations). And with preempt it
won't work at all, since we could changed the lru lists in another task
while the first one is walking them, leading ot all sorts of corruptions.

So I think it's better to just ignore UP (for now) and return a
conservative false here. Plus a comment explaining why.
-Daniel

> +#endif
> +}
> +
>  static int
>  i915_gem_inactive_shrink(struct shrinker *shrinker, struct shrink_control *sc)
>  {
> @@ -4350,10 +4362,15 @@ i915_gem_inactive_shrink(struct shrinker *shrinker, struct shrink_control *sc)
>  	struct drm_device *dev = dev_priv->dev;
>  	struct drm_i915_gem_object *obj;
>  	int nr_to_scan = sc->nr_to_scan;
> +	bool unlock = true;
>  	int cnt;
>  
> -	if (!mutex_trylock(&dev->struct_mutex))
> -		return 0;
> +	if (!mutex_trylock(&dev->struct_mutex)) {
> +		if (!mutex_is_locked_by(&dev->struct_mutex, current))
> +			return 0;
> +
> +		unlock = false;
> +	}
>  
>  	if (nr_to_scan) {
>  		nr_to_scan -= i915_gem_purge(dev_priv, nr_to_scan);
> @@ -4369,6 +4386,7 @@ i915_gem_inactive_shrink(struct shrinker *shrinker, struct shrink_control *sc)
>  		if (obj->pin_count == 0 && obj->pages_pin_count == 0)
>  			cnt += obj->base.size >> PAGE_SHIFT;
>  
> -	mutex_unlock(&dev->struct_mutex);
> +	if (unlock)
> +		mutex_unlock(&dev->struct_mutex);
>  	return cnt;
>  }
> -- 
> 1.7.10.4
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch