[PATCH] drm/i915: convert i915_active.count from atomic_t to refcount_t

[Deepak R Varma]

The refcount_* APIs are designed to address known issues with the
atomic_t APIs for reference counting. They provide following distinct
advantages:
   - protect the reference counters from overflow/underflow
   - avoid use-after-free errors
   - provide improved memory ordering guarantee schemes
   - neater and safer.
Hence, convert the atomic_t count member variable and associated
atomic_*() API calls to equivalent refcount_t type and refcount_*() API
calls.

This patch proposal address the following warnings generated by
the atomic_as_refcounter.cocci coccinelle script
	atomic_add_unless

Signed-off-by: Deepak R Varma <drv at mailo.com>
---
Please note: Proposed changes are compile tested only.

 drivers/gpu/drm/i915/i915_active.c       | 24 +++++++++++++-----------
 drivers/gpu/drm/i915/i915_active.h       |  6 +++---
 drivers/gpu/drm/i915/i915_active_types.h |  4 ++--
 3 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
index 7412abf166a8..4a8d873b4347 100644
--- a/drivers/gpu/drm/i915/i915_active.c
+++ b/drivers/gpu/drm/i915/i915_active.c
@@ -133,7 +133,7 @@ __active_retire(struct i915_active *ref)
 	GEM_BUG_ON(i915_active_is_idle(ref));

 	/* return the unused nodes to our slabcache -- flushing the allocator */
-	if (!atomic_dec_and_lock_irqsave(&ref->count, &ref->tree_lock, flags))
+	if (!refcount_dec_and_lock_irqsave(&ref->count, &ref->tree_lock, &flags))
 		return;

 	GEM_BUG_ON(rcu_access_pointer(ref->excl.fence));
@@ -179,8 +179,8 @@ active_work(struct work_struct *wrk)
 {
 	struct i915_active *ref = container_of(wrk, typeof(*ref), work);

-	GEM_BUG_ON(!atomic_read(&ref->count));
-	if (atomic_add_unless(&ref->count, -1, 1))
+	GEM_BUG_ON(!refcount_read(&ref->count));
+	if (refcount_dec_not_one(&ref->count))
 		return;

 	__active_retire(ref);
@@ -189,8 +189,8 @@ active_work(struct work_struct *wrk)
 static void
 active_retire(struct i915_active *ref)
 {
-	GEM_BUG_ON(!atomic_read(&ref->count));
-	if (atomic_add_unless(&ref->count, -1, 1))
+	GEM_BUG_ON(!refcount_read(&ref->count));
+	if (refcount_dec_not_one(&ref->count))
 		return;

 	if (ref->flags & I915_ACTIVE_RETIRE_SLEEPS) {
@@ -354,7 +354,7 @@ void __i915_active_init(struct i915_active *ref,
 	ref->cache = NULL;

 	init_llist_head(&ref->preallocated_barriers);
-	atomic_set(&ref->count, 0);
+	refcount_set(&ref->count, 0);
 	__mutex_init(&ref->mutex, "i915_active", mkey);
 	__i915_active_fence_init(&ref->excl, NULL, excl_retire);
 	INIT_WORK(&ref->work, active_work);
@@ -445,7 +445,7 @@ int i915_active_add_request(struct i915_active *ref, struct i915_request *rq)

 	if (replace_barrier(ref, active)) {
 		RCU_INIT_POINTER(active->fence, NULL);
-		atomic_dec(&ref->count);
+		refcount_dec(&ref->count);
 	}
 	if (!__i915_active_fence_set(active, fence))
 		__i915_active_acquire(ref);
@@ -488,14 +488,16 @@ i915_active_set_exclusive(struct i915_active *ref, struct dma_fence *f)
 bool i915_active_acquire_if_busy(struct i915_active *ref)
 {
 	debug_active_assert(ref);
-	return atomic_add_unless(&ref->count, 1, 0);
+	return refcount_add_not_zero(1, &ref->count);
 }

 static void __i915_active_activate(struct i915_active *ref)
 {
 	spin_lock_irq(&ref->tree_lock); /* __active_retire() */
-	if (!atomic_fetch_inc(&ref->count))
+	if (!refcount_inc_not_zero(&ref->count)) {
+		refcount_inc(&ref->count);
 		debug_active_activate(ref);
+	}
 	spin_unlock_irq(&ref->tree_lock);
 }

@@ -757,7 +759,7 @@ int i915_sw_fence_await_active(struct i915_sw_fence *fence,
 void i915_active_fini(struct i915_active *ref)
 {
 	debug_active_fini(ref);
-	GEM_BUG_ON(atomic_read(&ref->count));
+	GEM_BUG_ON(refcount_read(&ref->count));
 	GEM_BUG_ON(work_pending(&ref->work));
 	mutex_destroy(&ref->mutex);

@@ -927,7 +929,7 @@ int i915_active_acquire_preallocate_barrier(struct i915_active *ref,

 		first = first->next;

-		atomic_dec(&ref->count);
+		refcount_dec(&ref->count);
 		intel_engine_pm_put(barrier_to_engine(node));

 		kmem_cache_free(slab_cache, node);
diff --git a/drivers/gpu/drm/i915/i915_active.h b/drivers/gpu/drm/i915/i915_active.h
index 7eb44132183a..116c7c28466a 100644
--- a/drivers/gpu/drm/i915/i915_active.h
+++ b/drivers/gpu/drm/i915/i915_active.h
@@ -193,14 +193,14 @@ void i915_active_release(struct i915_active *ref);

 static inline void __i915_active_acquire(struct i915_active *ref)
 {
-	GEM_BUG_ON(!atomic_read(&ref->count));
-	atomic_inc(&ref->count);
+	GEM_BUG_ON(!refcount_read(&ref->count));
+	refcount_inc(&ref->count);
 }

 static inline bool
 i915_active_is_idle(const struct i915_active *ref)
 {
-	return !atomic_read(&ref->count);
+	return !refcount_read(&ref->count);
 }

 void i915_active_fini(struct i915_active *ref);
diff --git a/drivers/gpu/drm/i915/i915_active_types.h b/drivers/gpu/drm/i915/i915_active_types.h
index b02a78ac87db..152a3a25d9f7 100644
--- a/drivers/gpu/drm/i915/i915_active_types.h
+++ b/drivers/gpu/drm/i915/i915_active_types.h
@@ -7,7 +7,7 @@
 #ifndef _I915_ACTIVE_TYPES_H_
 #define _I915_ACTIVE_TYPES_H_

-#include <linux/atomic.h>
+#include <linux/refcount.h>
 #include <linux/dma-fence.h>
 #include <linux/llist.h>
 #include <linux/mutex.h>
@@ -23,7 +23,7 @@ struct i915_active_fence {
 struct active_node;

 struct i915_active {
-	atomic_t count;
+	refcount_t count;
 	struct mutex mutex;

 	spinlock_t tree_lock;
--
2.34.1