drm/i915: Add a spinlock to protect the active_list

This is a baby-step in the direction of having finer-grained
locking than the struct_mutex. Specifically, this will enable
new debugging code to read the active list for printing out
GPU state when the GPU is wedged, (while the struct_mutex is
held, of course).

Signed-off-by: Carl Worth <cworth@cworth.org>
[anholt: indentation fix]
Signed-off-by: Eric Anholt <eric@anholt.net>

4 files changed, 29 insertions, 4 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index c0f48bb366bf..317b1223e091 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -300,6 +300,7 @@ typedef struct drm_i915_private {
                  *
                  * A reference is held on the buffer while on this list.
                  */
+                spinlock_t active_list_lock;
                 struct list_head active_list;
 
                 /**
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 9f4eceb8093d..1449b452cc63 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1325,8 +1325,10 @@ i915_gem_object_move_to_active(struct drm_gem_object *obj, uint32_t seqno)
                 obj_priv->active = 1;
         }
         /* Move from whatever list we were on to the tail of execution. */
+        spin_lock(&dev_priv->mm.active_list_lock);
         list_move_tail(&obj_priv->list,
                        &dev_priv->mm.active_list);
+        spin_unlock(&dev_priv->mm.active_list_lock);
         obj_priv->last_rendering_seqno = seqno;
 }
 
@@ -1468,6 +1470,7 @@ i915_gem_retire_request(struct drm_device *dev,
         /* Move any buffers on the active list that are no longer referenced
          * by the ringbuffer to the flushing/inactive lists as appropriate.
          */
+        spin_lock(&dev_priv->mm.active_list_lock);
         while (!list_empty(&dev_priv->mm.active_list)) {
                 struct drm_gem_object *obj;
                 struct drm_i915_gem_object *obj_priv;
@@ -1482,7 +1485,7 @@ i915_gem_retire_request(struct drm_device *dev,
                  * this seqno.
                  */
                 if (obj_priv->last_rendering_seqno != request->seqno)
-                        return;
+                        goto out;
 
 #if WATCH_LRU
                 DRM_INFO("%s: retire %d moves to inactive list %p\n",
@@ -1494,6 +1497,8 @@ i915_gem_retire_request(struct drm_device *dev,
                 else
                         i915_gem_object_move_to_inactive(obj);
         }
+out:
+        spin_unlock(&dev_priv->mm.active_list_lock);
 }
 
 /**
@@ -2215,15 +2220,20 @@ i915_gem_object_bind_to_gtt(struct drm_gem_object *obj, unsigned alignment)
                 }
         }
         if (obj_priv->gtt_space == NULL) {
+                bool lists_empty;
+
                 /* If the gtt is empty and we're still having trouble
                  * fitting our object in, we're out of memory.
                  */
 #if WATCH_LRU
                 DRM_INFO("%s: GTT full, evicting something\n", __func__);
 #endif
-                if (list_empty(&dev_priv->mm.inactive_list) &&
-                    list_empty(&dev_priv->mm.flushing_list) &&
-                    list_empty(&dev_priv->mm.active_list)) {
+                spin_lock(&dev_priv->mm.active_list_lock);
+                lists_empty = (list_empty(&dev_priv->mm.inactive_list) &&
+                               list_empty(&dev_priv->mm.flushing_list) &&
+                               list_empty(&dev_priv->mm.active_list));
+                spin_unlock(&dev_priv->mm.active_list_lock);
+                if (lists_empty) {
                         DRM_ERROR("GTT full, but LRU list empty\n");
                         return -ENOMEM;
                 }
@@ -3679,6 +3689,7 @@ i915_gem_idle(struct drm_device *dev)
 
         i915_gem_retire_requests(dev);
 
+        spin_lock(&dev_priv->mm.active_list_lock);
         if (!dev_priv->mm.wedged) {
                 /* Active and flushing should now be empty as we've
                  * waited for a sequence higher than any pending execbuffer
@@ -3705,6 +3716,7 @@ i915_gem_idle(struct drm_device *dev)
                 obj_priv->obj->write_domain &= ~I915_GEM_GPU_DOMAINS;
                 i915_gem_object_move_to_inactive(obj_priv->obj);
         }
+        spin_unlock(&dev_priv->mm.active_list_lock);
 
         while (!list_empty(&dev_priv->mm.flushing_list)) {
                 struct drm_i915_gem_object *obj_priv;
@@ -3953,7 +3965,10 @@ i915_gem_entervt_ioctl(struct drm_device *dev, void *data,
         if (ret != 0)
                 return ret;
 
+        spin_lock(&dev_priv->mm.active_list_lock);
         BUG_ON(!list_empty(&dev_priv->mm.active_list));
+        spin_unlock(&dev_priv->mm.active_list_lock);
+
         BUG_ON(!list_empty(&dev_priv->mm.flushing_list));
         BUG_ON(!list_empty(&dev_priv->mm.inactive_list));
         BUG_ON(!list_empty(&dev_priv->mm.request_list));
@@ -3997,6 +4012,7 @@ i915_gem_load(struct drm_device *dev)
 {
         drm_i915_private_t *dev_priv = dev->dev_private;
 
+        spin_lock_init(&dev_priv->mm.active_list_lock);
         INIT_LIST_HEAD(&dev_priv->mm.active_list);
         INIT_LIST_HEAD(&dev_priv->mm.flushing_list);
         INIT_LIST_HEAD(&dev_priv->mm.inactive_list);
diff --git a/drivers/gpu/drm/i915/i915_gem_debug.c b/drivers/gpu/drm/i915/i915_gem_debug.c
index 131c088f8c8a..8d0b943e2c5a 100644
--- a/drivers/gpu/drm/i915/i915_gem_debug.c
+++ b/drivers/gpu/drm/i915/i915_gem_debug.c
@@ -105,12 +105,14 @@ i915_dump_lru(struct drm_device *dev, const char *where)
         struct drm_i915_gem_object      *obj_priv;
 
         DRM_INFO("active list %s {\n", where);
+        spin_lock(&dev_priv->mm.active_list_lock);
         list_for_each_entry(obj_priv, &dev_priv->mm.active_list,
                             list)
         {
                 DRM_INFO("    %p: %08x\n", obj_priv,
                          obj_priv->last_rendering_seqno);
         }
+        spin_unlock(&dev_priv->mm.active_list_lock);
         DRM_INFO("}\n");
         DRM_INFO("flushing list %s {\n", where);
         list_for_each_entry(obj_priv, &dev_priv->mm.flushing_list,
diff --git a/drivers/gpu/drm/i915/i915_gem_debugfs.c b/drivers/gpu/drm/i915/i915_gem_debugfs.c
index 455ec970b385..a1ac0c5e7307 100644
--- a/drivers/gpu/drm/i915/i915_gem_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_gem_debugfs.c
@@ -69,10 +69,13 @@ static int i915_gem_object_list_info(struct seq_file *m, void *data)
         struct drm_device *dev = node->minor->dev;
         drm_i915_private_t *dev_priv = dev->dev_private;
         struct drm_i915_gem_object *obj_priv;
+        spinlock_t *lock = NULL;
 
         switch (list) {
         case ACTIVE_LIST:
                 seq_printf(m, "Active:\n");
+                lock = &dev_priv->mm.active_list_lock;
+                spin_lock(lock);
                 head = &dev_priv->mm.active_list;
                 break;
         case INACTIVE_LIST:
@@ -104,6 +107,9 @@ static int i915_gem_object_list_info(struct seq_file *m, void *data)
                         seq_printf(m, " (fence: %d\n", obj_priv->fence_reg);
                 seq_printf(m, "\n");
         }
+
+        if (lock)
+            spin_unlock(lock);
         return 0;
 }