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: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/527843/
Link: https://lore.kernel.org/r/20230320144356.803762-9-robdclark@gmail.com

diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 58ac94507ff12e6dbc167cc2ee0752776599b6cc..b9171ac1a79a7b8fbaeb0998be52ede4d4ef7cfd 100644 (file)
--- 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 1929f09c5b0dc743379c4242f51bc24719c028ba..0057e8e8fa1355ea57918ac4554b0500759e83b0 100644 (file)
--- 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)