drm/i915/gtt: Make sure the gen6 ppgtt is bound before first use

As we remove the struct_mutex protection from around the vma pinning,
counters need to be atomic and aware that there may be multiple threads
simultaneously active.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190913064200.24297-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -1790,6 +1790,8 @@ static void gen6_ppgtt_cleanup(struct i915_address_space *vm)
 
 	gen6_ppgtt_free_pd(ppgtt);
 	free_scratch(vm);
+
+	mutex_destroy(&ppgtt->pin_mutex);
 	kfree(ppgtt->base.pd);
 }
 
@@ -1895,7 +1897,7 @@ static struct i915_vma *pd_vma_create(struct gen6_ppgtt *ppgtt, int size)
 int gen6_ppgtt_pin(struct i915_ppgtt *base)
 {
 	struct gen6_ppgtt *ppgtt = to_gen6_ppgtt(base);
-	int err;
+	int err = 0;
 
 	GEM_BUG_ON(ppgtt->base.vm.closed);
 
@@ -1905,24 +1907,26 @@ int gen6_ppgtt_pin(struct i915_ppgtt *base)
 	 * (When vma->pin_count becomes atomic, I expect we will naturally
 	 * need a larger, unpacked, type and kill this redundancy.)
 	 */
-	if (ppgtt->pin_count++)
+	if (atomic_add_unless(&ppgtt->pin_count, 1, 0))
 		return 0;
 
+	if (mutex_lock_interruptible(&ppgtt->pin_mutex))
+		return -EINTR;
+
 	/*
 	 * PPGTT PDEs reside in the GGTT and consists of 512 entries. The
 	 * allocator works in address space sizes, so it's multiplied by page
 	 * size. We allocate at the top of the GTT to avoid fragmentation.
 	 */
+	if (!atomic_read(&ppgtt->pin_count)) {
 		err = i915_vma_pin(ppgtt->vma,
 				   0, GEN6_PD_ALIGN,
 				   PIN_GLOBAL | PIN_HIGH);
-	if (err)
-		goto unpin;
-
-	return 0;
+	}
+	if (!err)
+		atomic_inc(&ppgtt->pin_count);
+	mutex_unlock(&ppgtt->pin_mutex);
 
-unpin:
-	ppgtt->pin_count = 0;
 	return err;
 }
 
@@ -1930,10 +1934,8 @@ void gen6_ppgtt_unpin(struct i915_ppgtt *base)
 {
 	struct gen6_ppgtt *ppgtt = to_gen6_ppgtt(base);
 
-	GEM_BUG_ON(!ppgtt->pin_count);
-	if (--ppgtt->pin_count)
-		return;
-
+	GEM_BUG_ON(!atomic_read(&ppgtt->pin_count));
+	if (atomic_dec_and_test(&ppgtt->pin_count))
 		i915_vma_unpin(ppgtt->vma);
 }
 
@@ -1941,11 +1943,11 @@ void gen6_ppgtt_unpin_all(struct i915_ppgtt *base)
 {
 	struct gen6_ppgtt *ppgtt = to_gen6_ppgtt(base);
 
-	if (!ppgtt->pin_count)
+	if (!atomic_read(&ppgtt->pin_count))
 		return;
 
-	ppgtt->pin_count = 0;
 	i915_vma_unpin(ppgtt->vma);
+	atomic_set(&ppgtt->pin_count, 0);
 }
 
 static struct i915_ppgtt *gen6_ppgtt_create(struct drm_i915_private *i915)
@@ -1958,6 +1960,8 @@ static struct i915_ppgtt *gen6_ppgtt_create(struct drm_i915_private *i915)
 	if (!ppgtt)
 		return ERR_PTR(-ENOMEM);
 
+	mutex_init(&ppgtt->pin_mutex);
+
 	ppgtt_init(&ppgtt->base, &i915->gt);
 	ppgtt->base.vm.top = 1;
 

drivers/gpu/drm/i915/i915_gem_gtt.h

@@ -437,7 +437,9 @@ struct gen6_ppgtt {
 	struct i915_vma *vma;
 	gen6_pte_t __iomem *pd_addr;
 
-	unsigned int pin_count;
+	atomic_t pin_count;
+	struct mutex pin_mutex;
+
 	bool scan_for_unused_pt;
 };