[PATCH v2 06/28] drm/i915: Ensure requests stick around during waits

John.C.Harrison
2014-11-14T12:19:28Z

Added reference counting of the request structure around __wait_seqno() calls.
This is a precursor to updating the wait code itself to take the request rather
than a seqno. At that point, it would be a Bad Idea for a request object to be
retired and freed while the wait code is still using it.

Note that i915_wait_request() is safe without reference counting as the driver
mutex lock is held for the duration. Thus it is not possible for a free to occur
asynchronously.

For: VIZ-4377
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
---
drivers/gpu/drm/i915/i915_gem.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 86c7aa0..4dbfee3 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1442,10 +1442,12 @@ i915_gem_object_wait_rendering__nonblocking(struct drm_i915_gem_object *obj,
return ret;

reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
+ i915_gem_request_reference(req);
mutex_unlock(&dev->struct_mutex);
ret = __i915_wait_seqno(ring, seqno, reset_counter, true, NULL,
file_priv);
mutex_lock(&dev->struct_mutex);
+ i915_gem_request_unreference(req);
if (ret)
return ret;

@@ -2904,6 +2906,7 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
struct drm_i915_private *dev_priv = dev->dev_private;
struct drm_i915_gem_wait *args = data;
struct drm_i915_gem_object *obj;
+ struct drm_i915_gem_request *req;
struct intel_engine_cs *ring = NULL;
unsigned reset_counter;
u32 seqno = 0;
@@ -2930,7 +2933,8 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
if (!obj->active || !obj->last_read_req)
goto out;

- seqno = i915_gem_request_get_seqno(obj->last_read_req);
+ req = obj->last_read_req;
+ seqno = i915_gem_request_get_seqno(req);
WARN_ON(seqno == 0);
ring = obj->ring;

@@ -2944,10 +2948,15 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)

drm_gem_object_unreference(&obj->base);
reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
+ i915_gem_request_reference(req);
mutex_unlock(&dev->struct_mutex);

- return __i915_wait_seqno(ring, seqno, reset_counter, true,
- &args->timeout_ns, file->driver_priv);
+ ret = __i915_wait_seqno(ring, seqno, reset_counter, true, &args->timeout_ns,
+ file->driver_priv);
+ mutex_lock(&dev->struct_mutex);
+ i915_gem_request_unreference(req);
+ mutex_unlock(&dev->struct_mutex);
+ return ret;

out:
drm_gem_object_unreference(&obj->base);
@@ -4106,6 +4115,8 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
target = request;
}
reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
+ if (target)
+ i915_gem_request_reference(target);
spin_unlock(&file_priv->mm.lock);

if (target == NULL)
@@ -4117,6 +4128,10 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
if (ret == 0)
queue_delayed_work(dev_priv->wq, &dev_priv->mm.retire_work, 0);

+ mutex_lock(&dev->struct_mutex);
+ i915_gem_request_unreference(target);
+ mutex_unlock(&dev->struct_mutex);
+
return ret;