drm/ttm: fix fence locking in ttm_buffer_object_transfer, 2nd try

This fixes up

commit e8e89622ed361c46bf90ba4828e685a8b603f7e5
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Tue Dec 18 22:25:11 2012 +0100

    drm/ttm: fix fence locking in ttm_buffer_object_transfer

which leaves behind a might_sleep in atomic context, since the
fence_lock spinlock is held over a kmalloc(GFP_KERNEL) call. The fix
is to revert the above commit and only take the lock where we need it,
around the call to ->sync_obj_ref.

v2: Fixup things noticed by Maarten Lankhorst:
- Brown paper bag locking bug.
- No need for kzalloc if we clear the entire thing on the next line.
- check for bo->sync_obj (totally unlikely race, but still someone
  else could have snuck in) and clear fbo->sync_obj if it's cleared
  already.

Reported-by: Dave Airlie <airlied@gmail.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
index 44420fca7dfa..8be35c809c7b 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -429,7 +429,7 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
         struct ttm_bo_device *bdev = bo->bdev;
         struct ttm_bo_driver *driver = bdev->driver;
 
-        fbo = kzalloc(sizeof(*fbo), GFP_KERNEL);
+        fbo = kmalloc(sizeof(*fbo), GFP_KERNEL);
         if (!fbo)
                 return -ENOMEM;
 
@@ -448,7 +448,12 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
         fbo->vm_node = NULL;
         atomic_set(&fbo->cpu_writers, 0);
 
-        fbo->sync_obj = driver->sync_obj_ref(bo->sync_obj);
+        spin_lock(&bdev->fence_lock);
+        if (bo->sync_obj)
+                fbo->sync_obj = driver->sync_obj_ref(bo->sync_obj);
+        else
+                fbo->sync_obj = NULL;
+        spin_unlock(&bdev->fence_lock);
         kref_init(&fbo->list_kref);
         kref_init(&fbo->kref);
         fbo->destroy = &ttm_transfered_destroy;
@@ -661,13 +666,11 @@ int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
                  */
 
                 set_bit(TTM_BO_PRIV_FLAG_MOVING, &bo->priv_flags);
-
-                /* ttm_buffer_object_transfer accesses bo->sync_obj */
-                ret = ttm_buffer_object_transfer(bo, &ghost_obj);
                 spin_unlock(&bdev->fence_lock);
                 if (tmp_obj)
                         driver->sync_obj_unref(&tmp_obj);
 
+                ret = ttm_buffer_object_transfer(bo, &ghost_obj);
                 if (ret)
                         return ret;