[PATCH 40/56] drm/i915: Pin the pages first in shmem prepare read/write

Chris Wilson chris at chris-wilson.co.uk
Fri Aug 12 19:15:22 UTC 2016


There is an improbable, but not impossible, case that if we leave the
pages unpin as we operate on the object, then somebody may steal the
lock (which lock? right now, it is struct_mutex, THE lock) and change the
cache domains after we have already inspected them.

(Whilst here, avail ourselves of the opportunity to take a couple of
steps to make the two functions look more similar.)

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c | 48 ++++++++++++++++++++++++-----------------
 1 file changed, 28 insertions(+), 20 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 62a060274f24..3d26db1634a7 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -613,6 +613,12 @@ int i915_gem_obj_prepare_shmem_read(struct drm_i915_gem_object *obj,
 	if (ret)
 		return ret;
 
+	ret = i915_gem_object_get_pages(obj);
+	if (ret)
+		return ret;
+
+	i915_gem_object_pin_pages(obj);
+
 	i915_gem_object_flush_gtt_write_domain(obj);
 
 	/* If we're not in the cpu read domain, set ourself into the gtt
@@ -624,22 +630,20 @@ int i915_gem_obj_prepare_shmem_read(struct drm_i915_gem_object *obj,
 		*needs_clflush = !cpu_cache_is_coherent(obj->base.dev,
 							obj->cache_level);
 
-	ret = i915_gem_object_get_pages(obj);
-	if (ret)
-		return ret;
-
-	i915_gem_object_pin_pages(obj);
-
 	if (*needs_clflush && !static_cpu_has(X86_FEATURE_CLFLUSH)) {
 		ret = i915_gem_object_set_to_cpu_domain(obj, false);
-		if (ret) {
-			i915_gem_object_unpin_pages(obj);
-			return ret;
-		}
+		if (ret)
+			goto err_unpin;
+
 		*needs_clflush = 0;
 	}
 
+	/* return with the pages pinned */
 	return 0;
+
+err_unpin:
+	i915_gem_object_unpin_pages(obj);
+	return ret;
 }
 
 int i915_gem_obj_prepare_shmem_write(struct drm_i915_gem_object *obj,
@@ -655,6 +659,12 @@ int i915_gem_obj_prepare_shmem_write(struct drm_i915_gem_object *obj,
 	if (ret)
 		return ret;
 
+	ret = i915_gem_object_get_pages(obj);
+	if (ret)
+		return ret;
+
+	i915_gem_object_pin_pages(obj);
+
 	i915_gem_object_flush_gtt_write_domain(obj);
 
 	/* If we're not in the cpu write domain, set ourself into the
@@ -672,18 +682,11 @@ int i915_gem_obj_prepare_shmem_write(struct drm_i915_gem_object *obj,
 		*needs_clflush |= !cpu_cache_is_coherent(obj->base.dev,
 							 obj->cache_level);
 
-	ret = i915_gem_object_get_pages(obj);
-	if (ret)
-		return ret;
-
-	i915_gem_object_pin_pages(obj);
-
 	if (*needs_clflush && !static_cpu_has(X86_FEATURE_CLFLUSH)) {
 		ret = i915_gem_object_set_to_cpu_domain(obj, true);
-		if (ret) {
-			i915_gem_object_unpin_pages(obj);
-			return ret;
-		}
+		if (ret)
+			goto err_unpin;
+
 		*needs_clflush = 0;
 	}
 
@@ -692,7 +695,12 @@ int i915_gem_obj_prepare_shmem_write(struct drm_i915_gem_object *obj,
 
 	intel_fb_obj_invalidate(obj, ORIGIN_CPU);
 	obj->dirty = 1;
+	/* return with the pages pinned */
 	return 0;
+
+err_unpin:
+	i915_gem_object_unpin_pages(obj);
+	return ret;
 }
 
 /* Per-page copy function for the shmem pread fastpath.
-- 
2.8.1



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