[Intel-gfx] [PATCH 14/37] drm/i915: Serialise i915_vma_pin_inplace() with i915_vma_unbind()

[Chris Wilson]

Directly seralise the atomic pinning with evicting the vma from unbind
with a pair of coupled cmpxchg to avoid fighting over vm->mutex.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_vma.c | 45 ++++++++++-----------------------
 1 file changed, 14 insertions(+), 31 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index dbe11b349175..17ce0bce318e 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -742,12 +742,10 @@ i915_vma_detach(struct i915_vma *vma)
 
 bool i915_vma_pin_inplace(struct i915_vma *vma, unsigned int flags)
 {
-	unsigned int bound;
-	bool pinned = true;
+	unsigned int bound = atomic_read(&vma->flags);
 
 	GEM_BUG_ON(flags & ~I915_VMA_BIND_MASK);
 
-	bound = atomic_read(&vma->flags);
 	do {
 		if (unlikely(flags & ~bound))
 			return false;
@@ -755,34 +753,10 @@ bool i915_vma_pin_inplace(struct i915_vma *vma, unsigned int flags)
 		if (unlikely(bound & (I915_VMA_OVERFLOW | I915_VMA_ERROR)))
 			return false;
 
-		if (!(bound & I915_VMA_PIN_MASK))
-			goto unpinned;
-
 		GEM_BUG_ON(((bound + 1) & I915_VMA_PIN_MASK) == 0);
 	} while (!atomic_try_cmpxchg(&vma->flags, &bound, bound + 1));
 
 	return true;
-
-unpinned:
-	/*
-	 * If pin_count==0, but we are bound, check under the lock to avoid
-	 * racing with a concurrent i915_vma_unbind().
-	 */
-	mutex_lock(&vma->vm->mutex);
-	do {
-		if (unlikely(bound & (I915_VMA_OVERFLOW | I915_VMA_ERROR))) {
-			pinned = false;
-			break;
-		}
-
-		if (unlikely(flags & ~bound)) {
-			pinned = false;
-			break;
-		}
-	} while (!atomic_try_cmpxchg(&vma->flags, &bound, bound + 1));
-	mutex_unlock(&vma->vm->mutex);
-
-	return pinned;
 }
 
 static int vma_get_pages(struct i915_vma *vma)
@@ -1292,6 +1266,7 @@ void __i915_vma_evict(struct i915_vma *vma)
 
 int __i915_vma_unbind(struct i915_vma *vma)
 {
+	unsigned int bound;
 	int ret;
 
 	lockdep_assert_held(&vma->vm->mutex);
@@ -1299,10 +1274,18 @@ int __i915_vma_unbind(struct i915_vma *vma)
 	if (!drm_mm_node_allocated(&vma->node))
 		return 0;
 
-	if (i915_vma_is_pinned(vma)) {
-		vma_print_allocator(vma, "is pinned");
-		return -EAGAIN;
-	}
+	/* Serialise with i915_vma_pin_inplace() */
+	bound = atomic_read(&vma->flags);
+	do {
+		if (unlikely(bound & I915_VMA_PIN_MASK)) {
+			vma_print_allocator(vma, "is pinned");
+			return -EAGAIN;
+		}
+
+		if (unlikely(bound & I915_VMA_ERROR))
+			break;
+	} while (!atomic_try_cmpxchg(&vma->flags,
+				     &bound, bound | I915_VMA_ERROR));
 
 	/*
 	 * After confirming that no one else is pinning this vma, wait for
-- 
2.20.1