[PATCH v2 4/5] drm/i915/gem: Fix same-driver-another-instance dma-buf export

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

If our exported dma-bufs are imported by another instance of our driver,
that instance will typically have the imported dma-bufs locked during
map_attachment(). But the exporter also locks the same reservation
object in the map_dma_buf() callback, which leads to recursive locking.

Add a live selftest to catch this case, and as a workaround until
we fully support dynamic import and export, declare the exporter dynamic
by providing NOP pin() and unpin() functions. This means our map_dma_buf()
callback will *always* get called locked, and by pinning unconditionally
in i915_gem_map_dma_buf() we make sure we don't need to use the
move_notify() functionality which is not yet implemented.

Reported-by: Ruhl, Michael J <michael.j.ruhl@intel.com>
Cc: Ruhl, Michael J <michael.j.ruhl@intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c    | 31 ++++++-
 .../drm/i915/gem/selftests/i915_gem_dmabuf.c  | 81 ++++++++++++++++++-
 2 files changed, 108 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
index 616c3a2f1baf..1d1eeb167d28 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
@@ -12,6 +12,8 @@
 #include "i915_gem_object.h"
 #include "i915_scatterlist.h"
 
+I915_SELFTEST_DECLARE(static bool force_different_devices;)
+
 static struct drm_i915_gem_object *dma_buf_to_obj(struct dma_buf *buf)
 {
 	return to_intel_bo(buf->priv);
@@ -25,7 +27,9 @@ static struct sg_table *i915_gem_map_dma_buf(struct dma_buf_attachment *attachme
 	struct scatterlist *src, *dst;
 	int ret, i;
 
-	ret = i915_gem_object_pin_pages_unlocked(obj);
+	assert_object_held(obj);
+
+	ret = i915_gem_object_pin_pages(obj);
 	if (ret)
 		goto err;
 
@@ -168,6 +172,26 @@ static int i915_gem_end_cpu_access(struct dma_buf *dma_buf, enum dma_data_direct
 	return err;
 }
 
+/*
+ * As a workaround until we fully support dynamic import and export,
+ * declare the exporter dynamic by providing NOP pin() and unpin() functions.
+ * This means our i915_gem_map_dma_buf() callback will *always* get called
+ * locked, and by pinning unconditionally in i915_gem_map_dma_buf() we make
+ * sure we don't need to use the move_notify() functionality which is
+ * not yet implemented. Typically for the same-driver-another-instance case,
+ * i915_gem_map_dma_buf() will be called at importer attach time and the
+ * mapped sg_list will be cached by the dma-buf core for the
+ * duration of the attachment.
+ */
+static int i915_gem_dmabuf_pin(struct dma_buf_attachment *attach)
+{
+	return 0;
+}
+
+static void i915_gem_dmabuf_unpin(struct dma_buf_attachment *attach)
+{
+}
+
 static const struct dma_buf_ops i915_dmabuf_ops =  {
 	.map_dma_buf = i915_gem_map_dma_buf,
 	.unmap_dma_buf = i915_gem_unmap_dma_buf,
@@ -177,6 +201,8 @@ static const struct dma_buf_ops i915_dmabuf_ops =  {
 	.vunmap = i915_gem_dmabuf_vunmap,
 	.begin_cpu_access = i915_gem_begin_cpu_access,
 	.end_cpu_access = i915_gem_end_cpu_access,
+	.pin = i915_gem_dmabuf_pin,
+	.unpin = i915_gem_dmabuf_unpin,
 };
 
 struct dma_buf *i915_gem_prime_export(struct drm_gem_object *gem_obj, int flags)
@@ -241,7 +267,8 @@ struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev,
 	if (dma_buf->ops == &i915_dmabuf_ops) {
 		obj = dma_buf_to_obj(dma_buf);
 		/* is it from our device? */
-		if (obj->base.dev == dev) {
+		if (obj->base.dev == dev &&
+		    !I915_SELFTEST_ONLY(force_different_devices)) {
 			/*
 			 * Importing dmabuf exported from out own gem increases
 			 * refcount on gem itself instead of f_count of dmabuf.
diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c
index dd74bc09ec88..24735d6c12a2 100644
--- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c
@@ -35,7 +35,7 @@ static int igt_dmabuf_export(void *arg)
 static int igt_dmabuf_import_self(void *arg)
 {
 	struct drm_i915_private *i915 = arg;
-	struct drm_i915_gem_object *obj;
+	struct drm_i915_gem_object *obj, *import_obj;
 	struct drm_gem_object *import;
 	struct dma_buf *dmabuf;
 	int err;
@@ -65,14 +65,90 @@ static int igt_dmabuf_import_self(void *arg)
 		err = -EINVAL;
 		goto out_import;
 	}
+	import_obj = to_intel_bo(import);
+
+	i915_gem_object_lock(import_obj, NULL);
+	err = ____i915_gem_object_get_pages(import_obj);
+	i915_gem_object_unlock(import_obj);
+	if (err) {
+		pr_err("Same object dma-buf get_pages failed!\n");
+		goto out_import;
+	}
 
 	err = 0;
 out_import:
-	i915_gem_object_put(to_intel_bo(import));
+	i915_gem_object_put(import_obj);
+out_dmabuf:
+	dma_buf_put(dmabuf);
+out:
+	i915_gem_object_put(obj);
+	return err;
+}
+
+static int igt_dmabuf_import_same_driver(void *arg)
+{
+	struct drm_i915_private *i915 = arg;
+	struct drm_i915_gem_object *obj, *import_obj;
+	struct drm_gem_object *import;
+	struct dma_buf *dmabuf;
+	int err;
+
+	force_different_devices = true;
+	obj = i915_gem_object_create_shmem(i915, PAGE_SIZE);
+	if (IS_ERR(obj))
+		goto out_ret;
+
+	dmabuf = i915_gem_prime_export(&obj->base, 0);
+	if (IS_ERR(dmabuf)) {
+		pr_err("i915_gem_prime_export failed with err=%d\n",
+		       (int)PTR_ERR(dmabuf));
+		err = PTR_ERR(dmabuf);
+		goto out;
+	}
+
+	import = i915_gem_prime_import(&i915->drm, dmabuf);
+	if (IS_ERR(import)) {
+		pr_err("i915_gem_prime_import failed with err=%d\n",
+		       (int)PTR_ERR(import));
+		err = PTR_ERR(import);
+		goto out_dmabuf;
+	}
+
+	if (import == &obj->base) {
+		pr_err("i915_gem_prime_import reused gem object!\n");
+		err = -EINVAL;
+		goto out_import;
+	}
+
+	import_obj = to_intel_bo(import);
+
+	i915_gem_object_lock(import_obj, NULL);
+	err = ____i915_gem_object_get_pages(import_obj);
+	if (err) {
+		pr_err("Different objects dma-buf get_pages failed!\n");
+		i915_gem_object_unlock(import_obj);
+		goto out_import;
+	}
+
+	/*
+	 * If the exported object is not in system memory, something
+	 * weird is going on. TODO: When p2p is supported, this is no
+	 * longer considered weird.
+	 */
+	if (obj->mm.region != i915->mm.regions[INTEL_REGION_SMEM]) {
+		pr_err("Exported dma-buf is not in system memory\n");
+		err = -EINVAL;
+	}
+	i915_gem_object_unlock(import_obj);
+
+out_import:
+	i915_gem_object_put(import_obj);
 out_dmabuf:
 	dma_buf_put(dmabuf);
 out:
 	i915_gem_object_put(obj);
+out_ret:
+	force_different_devices = false;
 	return err;
 }
 
@@ -286,6 +362,7 @@ int i915_gem_dmabuf_live_selftests(struct drm_i915_private *i915)
 {
 	static const struct i915_subtest tests[] = {
 		SUBTEST(igt_dmabuf_export),
+		SUBTEST(igt_dmabuf_import_same_driver),
 	};
 
 	return i915_subtests(tests, i915);
-- 
2.31.1