[v2,15/16] drm/i915: Remove support for unlocked i915_vma unbind

Commit Message

Maarten Lankhorst Nov. 29, 2021, 1:47 p.m. UTC

Now that we require the object lock for all ops, some code handling
race conditions can be removed.

This is required to not take short-term pins inside execbuf.

Signed-off-by: Maarten Lankhorst <[e-mail]>
Acked-by: Niranjana Vishwanathapura <[e-mail]>
---
 drivers/gpu/drm/i915/i915_vma.c | 40 +++++----------------------------
 1 file changed, 5 insertions(+), 35 deletions(-)

Patch

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index 100739b3e084..3236cf1c1400 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -776,7 +776,6 @@  i915_vma_detach(struct i915_vma *vma)
 static bool try_qad_pin(struct i915_vma *vma, unsigned int flags)
 {
 	unsigned int bound;
-	bool pinned = true;
 
 	bound = atomic_read(&vma->flags);
 	do {
@@ -786,34 +785,10 @@  static bool try_qad_pin(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 struct scatterlist *
@@ -1194,13 +1169,7 @@  __i915_vma_get_pages(struct i915_vma *vma)
 			vma->ggtt_view.type, ret);
 	}
 
-	pages = xchg(&vma->pages, pages);
-
-	/* did we race against a put_pages? */
-	if (pages && pages != vma->obj->mm.pages) {
-		sg_free_table(vma->pages);
-		kfree(vma->pages);
-	}
+	vma->pages = pages;
 
 	return ret;
 }
@@ -1234,13 +1203,14 @@  I915_SELFTEST_EXPORT int i915_vma_get_pages(struct i915_vma *vma)
 static void __vma_put_pages(struct i915_vma *vma, unsigned int count)
 {
 	/* We allocate under vma_get_pages, so beware the shrinker */
-	struct sg_table *pages = READ_ONCE(vma->pages);
+	struct sg_table *pages = vma->pages;
 
 	GEM_BUG_ON(atomic_read(&vma->pages_count) < count);
 
 	if (atomic_sub_return(count, &vma->pages_count) == 0) {
-		if (pages == cmpxchg(&vma->pages, pages, NULL) &&
-		    pages != vma->obj->mm.pages) {
+		vma->pages = NULL;
+
+		if (pages != vma->obj->mm.pages) {
 			sg_free_table(pages);
 			kfree(pages);
 		}