[Intel-gfx] [PATCH] drm/i915: Nuke struct_mutex from context_setparam

[Chris Wilson]

Userspace should be free to race against itself and shoot itself in
the foot if it so desires to adjust a parameter at the same time as
submitting a batch to that context. As such, the struct_mutex in context
setparam is only being used to serialise userspace against itself and
not for any protection of internal structs and so is superfluous.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/i915_gem_context.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 747b8170a15a..10fd742b591d 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -896,16 +896,12 @@ int i915_gem_context_setparam_ioctl(struct drm_device *dev, void *data,
 	struct drm_i915_file_private *file_priv = file->driver_priv;
 	struct drm_i915_gem_context_param *args = data;
 	struct i915_gem_context *ctx;
-	int ret;
+	int ret = 0;
 
 	ctx = i915_gem_context_lookup(file_priv, args->ctx_id);
 	if (!ctx)
 		return -ENOENT;
 
-	ret = i915_mutex_lock_interruptible(dev);
-	if (ret)
-		goto out;
-
 	switch (args->param) {
 	case I915_CONTEXT_PARAM_BAN_PERIOD:
 		ret = -EINVAL;
@@ -960,9 +956,7 @@ int i915_gem_context_setparam_ioctl(struct drm_device *dev, void *data,
 		ret = -EINVAL;
 		break;
 	}
-	mutex_unlock(&dev->struct_mutex);
 
-out:
 	i915_gem_context_put(ctx);
 	return ret;
 }
-- 
2.19.0.rc2