diff options
| -rw-r--r-- | drivers/gpu/drm/i915/i915_active.c | 30 |
1 files changed, 28 insertions, 2 deletions
diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c index e63578c80f53..89c34a69a2ea 100644 --- a/drivers/gpu/drm/i915/i915_active.c +++ b/drivers/gpu/drm/i915/i915_active.c @@ -157,6 +157,10 @@ __active_retire(struct i915_active *ref) rb_link_node(&ref->cache->node, NULL, &ref->tree.rb_node); rb_insert_color(&ref->cache->node, &ref->tree); GEM_BUG_ON(ref->tree.rb_node != &ref->cache->node); + + /* Make the cached node available for reuse with any timeline */ + if (IS_ENABLED(CONFIG_64BIT)) + ref->cache->timeline = 0; /* needs cmpxchg(u64) */ } spin_unlock_irqrestore(&ref->tree_lock, flags); @@ -235,6 +239,8 @@ static struct active_node *__active_lookup(struct i915_active *ref, u64 idx) { struct active_node *it; + GEM_BUG_ON(idx == 0); /* 0 is the unordered timeline, rsvd for cache */ + /* * We track the most recently used timeline to skip a rbtree search * for the common case, under typical loads we never need the rbtree @@ -243,8 +249,28 @@ static struct active_node *__active_lookup(struct i915_active *ref, u64 idx) * current timeline. */ it = READ_ONCE(ref->cache); - if (it && it->timeline == idx) - return it; + if (it) { + u64 cached = READ_ONCE(it->timeline); + + /* Once claimed, this slot will only belong to this idx */ + if (cached == idx) + return it; + +#ifdef CONFIG_64BIT /* for cmpxchg(u64) */ + /* + * An unclaimed cache [.timeline=0] can only be claimed once. + * + * If the value is already non-zero, some other thread has + * claimed the cache and we know that is does not match our + * idx. If, and only if, the timeline is currently zero is it + * worth competing to claim it atomically for ourselves (for + * only the winner of that race will cmpxchg return the old + * value of 0). + */ + if (!cached && !cmpxchg(&it->timeline, 0, idx)) + return it; +#endif + } BUILD_BUG_ON(offsetof(typeof(*it), node)); |