Commit 6c7c8fb8 authored by Rob Clark's avatar Rob Clark
Browse files

drm/msm/gem: Protect pin_count/madv by LRU lock 



Since the LRU lock is already acquired when moving an obj between LRUs,
we can use it to protect pin_count and madv, without any significant
change in locking (ie. it just expands the scope of the lock by a hand-
ful of instructions).  This prepares the way to decrement the pin_count
in the job_run() path without needing to hold the obj lock, to avoid a
potential deadlock (or rather stall) caused by the fence-signaling path
(job_run()) blocking on shrinker/reclaim.  (Only a stall because the
wait for fence signaling wait_for_idle() is not infinite.)

Signed-off-by: default avatarRob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/527843/
Link: https://lore.kernel.org/r/20230320144356.803762-9-robdclark@gmail.com
parent 4a02a376

drivers/gpu/drm/msm/msm_gem.c

+36 −12
Original line number Diff line number Diff line
@@ -61,7 +61,7 @@ static void sync_for_cpu(struct msm_gem_object *msm_obj) 
	dma_unmap_sgtable(dev, msm_obj->sgt, DMA_BIDIRECTIONAL, 0);

}



static void update_lru(struct drm_gem_object *obj)

static void update_lru_locked(struct drm_gem_object *obj)

{

	struct msm_drm_private *priv = obj->dev->dev_private;

	struct msm_gem_object *msm_obj = to_msm_bo(obj);
@@ -71,18 +71,27 @@ static void update_lru(struct drm_gem_object *obj) 
	if (!msm_obj->pages) {

		GEM_WARN_ON(msm_obj->pin_count);



		drm_gem_lru_move_tail(&priv->lru.unbacked, obj);

		drm_gem_lru_move_tail_locked(&priv->lru.unbacked, obj);

	} else if (msm_obj->pin_count) {

		drm_gem_lru_move_tail(&priv->lru.pinned, obj);

		drm_gem_lru_move_tail_locked(&priv->lru.pinned, obj);

	} else if (msm_obj->madv == MSM_MADV_WILLNEED) {

		drm_gem_lru_move_tail(&priv->lru.willneed, obj);

		drm_gem_lru_move_tail_locked(&priv->lru.willneed, obj);

	} else {

		GEM_WARN_ON(msm_obj->madv != MSM_MADV_DONTNEED);



		drm_gem_lru_move_tail(&priv->lru.dontneed, obj);

		drm_gem_lru_move_tail_locked(&priv->lru.dontneed, obj);

	}

}



static void update_lru(struct drm_gem_object *obj)

{

	struct msm_drm_private *priv = obj->dev->dev_private;



	mutex_lock(&priv->lru.lock);

	update_lru_locked(obj);

	mutex_unlock(&priv->lru.lock);

}



/* allocate pages from VRAM carveout, used when no IOMMU: */

static struct page **get_pages_vram(struct drm_gem_object *obj, int npages)

{
@@ -200,6 +209,7 @@ static void put_pages(struct drm_gem_object *obj) 


static struct page **msm_gem_pin_pages_locked(struct drm_gem_object *obj)

{

	struct msm_drm_private *priv = obj->dev->dev_private;

	struct msm_gem_object *msm_obj = to_msm_bo(obj);

	struct page **p;
@@ -210,10 +220,13 @@ static struct page **msm_gem_pin_pages_locked(struct drm_gem_object *obj) 
	}



	p = get_pages(obj);

	if (!IS_ERR(p)) {

		to_msm_bo(obj)->pin_count++;

		update_lru(obj);

	}

	if (IS_ERR(p))

		return p;



	mutex_lock(&priv->lru.lock);

	msm_obj->pin_count++;

	update_lru_locked(obj);

	mutex_unlock(&priv->lru.lock);



	return p;

}
@@ -464,14 +477,16 @@ int msm_gem_pin_vma_locked(struct drm_gem_object *obj, struct msm_gem_vma *vma) 


void msm_gem_unpin_locked(struct drm_gem_object *obj)

{

	struct msm_drm_private *priv = obj->dev->dev_private;

	struct msm_gem_object *msm_obj = to_msm_bo(obj);



	msm_gem_assert_locked(obj);



	mutex_lock(&priv->lru.lock);

	msm_obj->pin_count--;

	GEM_WARN_ON(msm_obj->pin_count < 0);



	update_lru(obj);

	update_lru_locked(obj);

	mutex_unlock(&priv->lru.lock);

}



struct msm_gem_vma *msm_gem_get_vma_locked(struct drm_gem_object *obj,
@@ -739,10 +754,13 @@ void msm_gem_put_vaddr(struct drm_gem_object *obj) 
 */

int msm_gem_madvise(struct drm_gem_object *obj, unsigned madv)

{

	struct msm_drm_private *priv = obj->dev->dev_private;

	struct msm_gem_object *msm_obj = to_msm_bo(obj);



	msm_gem_lock(obj);



	mutex_lock(&priv->lru.lock);



	if (msm_obj->madv != __MSM_MADV_PURGED)

		msm_obj->madv = madv;
@@ -751,7 +769,9 @@ int msm_gem_madvise(struct drm_gem_object *obj, unsigned madv) 
	/* If the obj is inactive, we might need to move it

	 * between inactive lists

	 */

	update_lru(obj);

	update_lru_locked(obj);



	mutex_unlock(&priv->lru.lock);



	msm_gem_unlock(obj);
@@ -761,6 +781,7 @@ int msm_gem_madvise(struct drm_gem_object *obj, unsigned madv) 
void msm_gem_purge(struct drm_gem_object *obj)

{

	struct drm_device *dev = obj->dev;

	struct msm_drm_private *priv = obj->dev->dev_private;

	struct msm_gem_object *msm_obj = to_msm_bo(obj);



	msm_gem_assert_locked(obj);
@@ -777,7 +798,10 @@ void msm_gem_purge(struct drm_gem_object *obj) 


	put_iova_vmas(obj);



	mutex_lock(&priv->lru.lock);

	/* A one-way transition: */

	msm_obj->madv = __MSM_MADV_PURGED;

	mutex_unlock(&priv->lru.lock);



	drm_gem_free_mmap_offset(obj);

drivers/gpu/drm/msm/msm_gem.h

+8 −1
Original line number Diff line number Diff line
@@ -86,7 +86,9 @@ struct msm_gem_object { 
	uint32_t flags;



	/**

	 * Advice: are the backing pages purgeable?

	 * madv: are the backing pages purgeable?

	 *

	 * Protected by obj lock and LRU lock

	 */

	uint8_t madv;
@@ -114,6 +116,11 @@ struct msm_gem_object { 


	char name[32]; /* Identifier to print for the debugfs files */



	/**

	 * pin_count: Number of times the pages are pinned

	 *

	 * Protected by LRU lock.

	 */

	int pin_count;

};

#define to_msm_bo(x) container_of(x, struct msm_gem_object, base)