diff options
Diffstat (limited to 'drivers/gpu')
| -rw-r--r-- | drivers/gpu/drm/i915/i915_gem_request.h | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/drivers/gpu/drm/i915/i915_gem_request.h b/drivers/gpu/drm/i915/i915_gem_request.h index 6c72bd8d9423..91014de8bfbc 100644 --- a/drivers/gpu/drm/i915/i915_gem_request.h +++ b/drivers/gpu/drm/i915/i915_gem_request.h @@ -472,6 +472,19 @@ __i915_gem_active_get_rcu(const struct i915_gem_active *active) if (!request || i915_gem_request_completed(request)) return NULL; + /* An especially silly compiler could decide to recompute the + * result of i915_gem_request_completed, more specifically + * re-emit the load for request->fence.seqno. A race would catch + * a later seqno value, which could flip the result from true to + * false. Which means part of the instructions below might not + * be executed, while later on instructions are executed. Due to + * barriers within the refcounting the inconsistency can't reach + * past the call to i915_gem_request_get_rcu, but not executing + * that while still executing i915_gem_request_put() creates + * havoc enough. Prevent this with a compiler barrier. + */ + barrier(); + request = i915_gem_request_get_rcu(request); /* What stops the following rcu_access_pointer() from occurring |