Otherwise we end up trying to unpin a freed object and BUG.

Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Ben Widawsky <b...@bwidawsk.net>
---
 drivers/gpu/drm/i915/i915_gem_context.c |   82 +++++++++++--------------------
 1 file changed, 30 insertions(+), 52 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c 
b/drivers/gpu/drm/i915/i915_gem_context.c
index 90857f8..b0a855f 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -97,8 +97,7 @@
 
 static struct i915_hw_context *
 i915_gem_context_get(struct drm_i915_file_private *file_priv, u32 id);
-static int do_switch(struct drm_i915_gem_object *from_obj,
-                    struct i915_hw_context *to, u32 seqno);
+static int do_switch(struct i915_hw_context *to);
 
 static int get_context_size(struct drm_device *dev)
 {
@@ -220,26 +219,24 @@ static int create_default_context(struct drm_i915_private 
*dev_priv)
         */
        dev_priv->ring[RCS].default_context = ctx;
        ret = i915_gem_object_pin(ctx->obj, CONTEXT_ALIGN, false);
-       if (ret) {
-               do_destroy(ctx);
-               return ret;
-       }
+       if (ret)
+               goto err_destroy;
 
        ret = i915_gem_object_set_to_gtt_domain(ctx->obj, true);
-       if (ret) {
-               i915_gem_object_unpin(ctx->obj);
-               do_destroy(ctx);
-               return ret;
-       }
+       if (ret)
+               goto err_unpin;
 
-       ret = do_switch(NULL, ctx, 0);
-       if (ret) {
-               i915_gem_object_unpin(ctx->obj);
-               do_destroy(ctx);
-       } else {
-               DRM_DEBUG_DRIVER("Default HW context loaded\n");
-       }
+       ret = do_switch(ctx);
+       if (ret)
+               goto err_unpin;
 
+       DRM_DEBUG_DRIVER("Default HW context loaded\n");
+       return 0;
+
+err_unpin:
+       i915_gem_object_unpin(ctx->obj);
+err_destroy:
+       do_destroy(ctx);
        return ret;
 }
 
@@ -366,16 +363,14 @@ mi_set_context(struct intel_ring_buffer *ring,
        return ret;
 }
 
-static int do_switch(struct drm_i915_gem_object *from_obj,
-                    struct i915_hw_context *to,
-                    u32 seqno)
+static int do_switch(struct i915_hw_context *to)
 {
-       struct intel_ring_buffer *ring = NULL;
+       struct drm_i915_gem_object *from_obj = to->ring->last_context_obj;
        u32 hw_flags = 0;
        int ret;
 
-       BUG_ON(to == NULL);
-       BUG_ON(from_obj != NULL && from_obj->pin_count == 0);
+       if (from_obj == to->obj)
+               return 0;
 
        ret = i915_gem_object_pin(to->obj, CONTEXT_ALIGN, false);
        if (ret)
@@ -389,8 +384,7 @@ static int do_switch(struct drm_i915_gem_object *from_obj,
        else if (WARN_ON_ONCE(from_obj == to->obj)) /* not yet expected */
                hw_flags |= MI_FORCE_RESTORE;
 
-       ring = to->ring;
-       ret = mi_set_context(ring, to, hw_flags);
+       ret = mi_set_context(to->ring, to, hw_flags);
        if (ret) {
                i915_gem_object_unpin(to->obj);
                return ret;
@@ -403,6 +397,7 @@ static int do_switch(struct drm_i915_gem_object *from_obj,
         * MI_SET_CONTEXT instead of when the next seqno has completed.
         */
        if (from_obj != NULL) {
+               u32 seqno = i915_gem_next_request_seqno(to->ring);
                /* As long as MI_SET_CONTEXT is serializing, ie. it flushes the
                 * whole damn pipeline, we don't need to explicitly mark the
                 * object dirty. The only exception is that the context must be
@@ -412,13 +407,15 @@ static int do_switch(struct drm_i915_gem_object *from_obj,
                 */
                from_obj->base.write_domain = I915_GEM_DOMAIN_INSTRUCTION;
                from_obj->base.read_domains = I915_GEM_DOMAIN_INSTRUCTION;
-               i915_gem_object_move_to_active(from_obj, ring, seqno);
+               i915_gem_object_move_to_active(from_obj, to->ring, seqno);
                from_obj->dirty = 1;
                BUG_ON(from_obj->ring != to->ring);
                i915_gem_object_unpin(from_obj);
+               drm_gem_object_unreference(&from_obj->base);
        }
 
-       ring->last_context_obj = to->obj;
+       drm_gem_object_reference(&to->obj->base);
+       to->ring->last_context_obj = to->obj;
        to->is_initialized = true;
 
        return 0;
@@ -442,10 +439,7 @@ int i915_switch_context(struct intel_ring_buffer *ring,
                        int to_id)
 {
        struct drm_i915_private *dev_priv = ring->dev->dev_private;
-       struct drm_i915_file_private *file_priv = NULL;
        struct i915_hw_context *to;
-       struct drm_i915_gem_object *from_obj = ring->last_context_obj;
-       int ret;
 
        if (dev_priv->hw_contexts_disabled)
                return 0;
@@ -453,34 +447,18 @@ int i915_switch_context(struct intel_ring_buffer *ring,
        if (ring != &dev_priv->ring[RCS])
                return 0;
 
-       if (file)
-               file_priv = file->driver_priv;
-
        if (to_id == DEFAULT_CONTEXT_ID) {
                to = ring->default_context;
        } else {
-               to = i915_gem_context_get(file_priv, to_id);
+               if (file == NULL)
+                       return -EINVAL;
+
+               to = i915_gem_context_get(file->driver_priv, to_id);
                if (to == NULL)
                        return -ENOENT;
        }
 
-       if (from_obj == to->obj)
-               return 0;
-
-       ret = do_switch(from_obj, to, i915_gem_next_request_seqno(to->ring));
-       if (ret)
-               return ret;
-
-       /* Just to make the code a little cleaner we take the object reference
-        * after the switch was successful. It would be more intuitive to ref
-        * the 'to' object before the switch but we know the refcount must be >0
-        * if context_get() succeeded, and we hold struct mutex. So it's safe to
-        * do this here/now
-        */
-       drm_gem_object_reference(&to->obj->base);
-       if (from_obj != NULL)
-               drm_gem_object_unreference(&from_obj->base);
-       return ret;
+       return do_switch(to);
 }
 
 int i915_gem_context_create_ioctl(struct drm_device *dev, void *data,
-- 
1.7.10.4

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