New subject: [PATCH 2/2] drm: prime: fix refcounting on the dmabuf import error path

19 Apr 2013

Currently we have a problem with this:
1. i915: create gem object
2. i915: export gem object to prime
3. radeon: import gem object
4. close prime fd
5. radeon: unref object
6. i915: unref object
i915 has an imported object reference in its file priv, that isn't
cleaned up properly until fd close. The reference gets added at step 2,
but at step 6 we don't have enough info to clean it up.
The solution is to take a reference on the dma-buf when we export it,
and drop the reference when the gem handle goes away.
So when we export a dma_buf from a gem object, we keep track of it
with the handle, we take a reference to the dma_buf. When we close
the handle (i.e. userspace is finished with the buffer), we drop
the reference to the dma_buf, and it gets collected.
This patch isn't meant to fix any other problem or bikesheds, and it doesn't
fix any races with other scenarios.
v1.1: move export symbol line back up.
v2: okay I had to do a bit more, as the first patch showed a leak
on one of my tests, that I found using the dma-buf debugfs support,
the problem case is exporting a buffer twice with the same handle,
we'd add another export handle for it unnecessarily, however
we now fail if we try to export the same object with a different gem handle,
however I'm not sure if that is a case I want to support, and I've
gotten the code to WARN_ON if we hit something like that.
v2.1: rebase this patch, write better commit msg.
v3: cleanup error handling, track import vs export in linked list,
these two patches were separate previously, but seem to work better
like this.
v4: danvet is correct, this code is no longer useful, since the buffer
better exist, so remove it.
v5: always take a reference to the dma buf object, import or export.
(Imre Deak contributed this originally)
Signed-off-by: Dave Airlie airlied@redhat.com
---
 drivers/gpu/drm/drm_gem.c   |  4 +-
 drivers/gpu/drm/drm_prime.c | 93 ++++++++++++++++++++++++++++-----------------
 include/drm/drmP.h          |  4 +-
 3 files changed, 63 insertions(+), 38 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index af779ae..cf919e3 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -205,11 +205,11 @@ static void
 drm_gem_remove_prime_handles(struct drm_gem_object *obj, struct drm_file *filp)
 {
    if (obj->import_attach) {
-		drm_prime_remove_imported_buf_handle(&filp->prime,
+		drm_prime_remove_buf_handle(&filp->prime,
    			obj->import_attach->dmabuf);
    }
    if (obj->export_dma_buf) {
-		drm_prime_remove_imported_buf_handle(&filp->prime,
+		drm_prime_remove_buf_handle(&filp->prime,
    			obj->export_dma_buf);
    }
 }
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 366910d..eb7c38d 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -57,10 +57,14 @@
  * use the drm_gem_prime_{import,export} helpers.
  */
+#define PRIME_IMPORT 1
+#define PRIME_EXPORT 2
+
 struct drm_prime_member {
    struct list_head entry;
    struct dma_buf *dma_buf;
    uint32_t handle;
+	int type;
 };
static struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
@@ -157,6 +161,8 @@ static const struct dma_buf_ops drm_gem_prime_dmabuf_ops =  {
    .vunmap = drm_gem_dmabuf_vunmap,
 };
+static int drm_prime_add_exported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle);
+
 /**
  * DOC: PRIME Helpers
  *
@@ -200,7 +206,8 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
 {
    struct drm_gem_object *obj;
    void *buf;
-	int ret;
+	int ret = 0;
+	struct dma_buf *dmabuf;
obj = drm_gem_object_lookup(dev, file_priv, handle);
    if (!obj)
@@ -209,43 +216,44 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
    mutex_lock(&file_priv->prime.lock);
    /* re-export the original imported object */
    if (obj->import_attach) {
-		get_dma_buf(obj->import_attach->dmabuf);
-		*prime_fd = dma_buf_fd(obj->import_attach->dmabuf, flags);
-		drm_gem_object_unreference_unlocked(obj);
-		mutex_unlock(&file_priv->prime.lock);
-		return 0;
+		dmabuf = obj->import_attach->dmabuf;
+		goto out_have_obj;
    }
if (obj->export_dma_buf) {
-		get_dma_buf(obj->export_dma_buf);
-		*prime_fd = dma_buf_fd(obj->export_dma_buf, flags);
-		drm_gem_object_unreference_unlocked(obj);
-	} else {
-		buf = dev->driver->gem_prime_export(dev, obj, flags);
-		if (IS_ERR(buf)) {
-			/* normally the created dma-buf takes ownership of the ref,
-			 * but if that fails then drop the ref
-			 */
-			drm_gem_object_unreference_unlocked(obj);
-			mutex_unlock(&file_priv->prime.lock);
-			return PTR_ERR(buf);
-		}
-		obj->export_dma_buf = buf;
-		*prime_fd = dma_buf_fd(buf, flags);
+		dmabuf = obj->export_dma_buf;
+		goto out_have_obj;
    }
+
+	buf = dev->driver->gem_prime_export(dev, obj, flags);
+	if (IS_ERR(buf)) {
+		/* normally the created dma-buf takes ownership of the ref,
+		 * but if that fails then drop the ref
+		 */
+		ret = PTR_ERR(buf);
+		goto out;
+	}
+	obj->export_dma_buf = buf;
+
    /* if we've exported this buffer the cheat and add it to the import list
     * so we get the correct handle back
     */
-	ret = drm_prime_add_imported_buf_handle(&file_priv->prime,
-			obj->export_dma_buf, handle);
-	if (ret) {
-		drm_gem_object_unreference_unlocked(obj);
-		mutex_unlock(&file_priv->prime.lock);
-		return ret;
-	}
+	ret = drm_prime_add_exported_buf_handle(&file_priv->prime,
+						obj->export_dma_buf, handle);
+	if (ret)
+		goto out;
+	*prime_fd = dma_buf_fd(buf, flags);
    mutex_unlock(&file_priv->prime.lock);
    return 0;
+
+out_have_obj:
+	get_dma_buf(dmabuf);
+	*prime_fd = dma_buf_fd(dmabuf, flags);
+out:
+	drm_gem_object_unreference_unlocked(obj);
+	mutex_unlock(&file_priv->prime.lock);
+	return ret;
 }
 EXPORT_SYMBOL(drm_gem_prime_handle_to_fd);
@@ -314,7 +322,7 @@ int drm_gem_prime_fd_to_handle(struct drm_device *dev,
mutex_lock(&file_priv->prime.lock);
-	ret = drm_prime_lookup_imported_buf_handle(&file_priv->prime,
+	ret = drm_prime_lookup_buf_handle(&file_priv->prime,
    		dma_buf, handle);
    if (!ret) {
    	ret = 0;
@@ -491,7 +499,7 @@ void drm_prime_destroy_file_private(struct drm_prime_file_private *prime_fpriv)
 }
 EXPORT_SYMBOL(drm_prime_destroy_file_private);
-int drm_prime_add_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle)
+static int drm_prime_add_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle, int type)
 {
    struct drm_prime_member *member;
@@ -499,14 +507,27 @@ int drm_prime_add_imported_buf_handle(struct drm_prime_file_private *prime_fpriv
    if (!member)
    	return -ENOMEM;
+	get_dma_buf(dma_buf);
    member->dma_buf = dma_buf;
    member->handle = handle;
+	member->type = type;
    list_add(&member->entry, &prime_fpriv->head);
    return 0;
 }
+
+int drm_prime_add_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle)
+{
+	return drm_prime_add_buf_handle(prime_fpriv, dma_buf, handle, PRIME_IMPORT);
+}
 EXPORT_SYMBOL(drm_prime_add_imported_buf_handle);
-int drm_prime_lookup_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t *handle)
+static int drm_prime_add_exported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle)
+{
+	/* take a reference to the buf handle for this case */
+	return drm_prime_add_buf_handle(prime_fpriv, dma_buf, handle, PRIME_EXPORT);
+}
+
+int drm_prime_lookup_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t *handle)
 {
    struct drm_prime_member *member;
@@ -518,19 +539,23 @@ int drm_prime_lookup_imported_buf_handle(struct drm_prime_file_private *prime_fp
    }
    return -ENOENT;
 }
-EXPORT_SYMBOL(drm_prime_lookup_imported_buf_handle);
+EXPORT_SYMBOL(drm_prime_lookup_buf_handle);
-void drm_prime_remove_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf)
+void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf)
 {
    struct drm_prime_member *member, *safe;
mutex_lock(&prime_fpriv->lock);
    list_for_each_entry_safe(member, safe, &prime_fpriv->head, entry) {
    	if (member->dma_buf == dma_buf) {
+			dma_buf_put(dma_buf);
    		list_del(&member->entry);
    		kfree(member);
    	}
    }
    mutex_unlock(&prime_fpriv->lock);
 }
-EXPORT_SYMBOL(drm_prime_remove_imported_buf_handle);
+EXPORT_SYMBOL(drm_prime_remove_buf_handle);
+
+
+
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 2d94d74..69712a6 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -1594,8 +1594,8 @@ extern void drm_prime_gem_destroy(struct drm_gem_object *obj, struct sg_table *s
 void drm_prime_init_file_private(struct drm_prime_file_private *prime_fpriv);
 void drm_prime_destroy_file_private(struct drm_prime_file_private *prime_fpriv);
 int drm_prime_add_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle);
-int drm_prime_lookup_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t *handle);
-void drm_prime_remove_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf);
+int drm_prime_lookup_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t *handle);
+void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf);
int drm_prime_add_dma_buf(struct drm_device *dev, struct drm_gem_object *obj);
 int drm_prime_lookup_obj(struct drm_device *dev, struct dma_buf *buf,
-- 
1.8.2


    

[PATCH 1/2] drm/prime: keep a reference from the handle to exported dma-buf (v5)

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