[PATCH v2 08/23] drm/msm/gem: Protect pin_count/madv by LRU lock

Rob Clark
2023-03-20T14:45:30Z

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: Rob Clark <robdclark@chromium.org>
---
drivers/gpu/drm/msm/msm_gem.c | 48 ++++++++++++++++++++++++++---------
drivers/gpu/drm/msm/msm_gem.h | 9 ++++++-
2 files changed, 44 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index c97dddf3e2f2..d0ac3e704b66 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -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);

diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
index 1929f09c5b0d..0057e8e8fa13 100644
--- a/drivers/gpu/drm/msm/msm_gem.h
+++ b/drivers/gpu/drm/msm/msm_gem.h
@@ -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)
--
2.39.2