drm/i915: Convert the file mutex into a spinlock

Daniel Vetter pointed out that in this case is would be clearer and
cleaner to use a spinlock instead of a mutex to protect the per-file
request list manipulation. Make it so.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

3 files changed, 17 insertions, 15 deletions

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index ba050ed8df51..b752c31fbcff 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -2173,8 +2173,8 @@ int i915_driver_open(struct drm_device *dev, struct drm_file *file)
 
         file->driver_priv = file_priv;
 
+        spin_lock_init(&file_priv->mm.lock);
         INIT_LIST_HEAD(&file_priv->mm.request_list);
-        mutex_init(&file_priv->mutex);
 
         return 0;
 }
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index f2ff258cdfd5..710d59ea479c 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -851,8 +851,8 @@ struct drm_i915_gem_request {
 };
 
 struct drm_i915_file_private {
-        struct mutex mutex;
         struct {
+                struct spinlock lock;
                 struct list_head request_list;
         } mm;
 };
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index ac5bff85a4c7..78282edc02ca 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1694,11 +1694,11 @@ i915_add_request(struct drm_device *dev,
         list_add_tail(&request->list, &ring->request_list);
 
         if (file_priv) {
-                mutex_lock(&file_priv->mutex);
+                spin_lock(&file_priv->mm.lock);
                 request->file_priv = file_priv;
                 list_add_tail(&request->client_list,
                               &file_priv->mm.request_list);
-                mutex_unlock(&file_priv->mutex);
+                spin_unlock(&file_priv->mm.lock);
         }
 
         if (!dev_priv->mm.suspended) {
@@ -1733,11 +1733,15 @@ i915_retire_commands(struct drm_device *dev, struct intel_ring_buffer *ring)
 static inline void
 i915_gem_request_remove_from_client(struct drm_i915_gem_request *request)
 {
-        if (request->file_priv) {
-                mutex_lock(&request->file_priv->mutex);
-                list_del(&request->client_list);
-                mutex_unlock(&request->file_priv->mutex);
-        }
+        struct drm_i915_file_private *file_priv = request->file_priv;
+
+        if (!file_priv)
+                return;
+
+        spin_lock(&file_priv->mm.lock);
+        list_del(&request->client_list);
+        request->file_priv = NULL;
+        spin_unlock(&file_priv->mm.lock);
 }
 
 static void i915_gem_reset_ring_lists(struct drm_i915_private *dev_priv,
@@ -3464,7 +3468,7 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
         u32 seqno = 0;
         int ret;
 
-        mutex_lock(&file_priv->mutex);
+        spin_lock(&file_priv->mm.lock);
         list_for_each_entry(request, &file_priv->mm.request_list, client_list) {
                 if (time_after_eq(request->emitted_jiffies, recent_enough))
                         break;
@@ -3472,7 +3476,7 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
                 ring = request->ring;
                 seqno = request->seqno;
         }
-        mutex_unlock(&file_priv->mutex);
+        spin_unlock(&file_priv->mm.lock);
 
         if (seqno == 0)
                 return 0;
@@ -4974,8 +4978,7 @@ void i915_gem_release(struct drm_device *dev, struct drm_file *file)
          * later retire_requests won't dereference our soon-to-be-gone
          * file_priv.
          */
-        mutex_lock(&dev->struct_mutex);
-        mutex_lock(&file_priv->mutex);
+        spin_lock(&file_priv->mm.lock);
         while (!list_empty(&file_priv->mm.request_list)) {
                 struct drm_i915_gem_request *request;
 
@@ -4985,8 +4988,7 @@ void i915_gem_release(struct drm_device *dev, struct drm_file *file)
                 list_del(&request->client_list);
                 request->file_priv = NULL;
         }
-        mutex_unlock(&file_priv->mutex);
-        mutex_unlock(&dev->struct_mutex);
+        spin_unlock(&file_priv->mm.lock);
 }
 
 static int