drm/prime: keep a reference from the handle to exported dma-buf (v6)

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)
v6: square the circle, remove import vs export tracking now
that there is no difference

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index af779ae..cf919e3 100644 (file)
--- 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 25d0218..7830d8e 100644 (file)
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -62,6 +62,7 @@ struct drm_prime_member {
        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);
 
 static struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
                enum dma_data_direction dir)
@@ -200,7 +201,8 @@ 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 +211,44 @@ 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_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 +317,7 @@ 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;
@@ -333,7 +336,7 @@ int drm_gem_prime_fd_to_handle(struct drm_device *dev,
        if (ret)
                goto out_put;
 
-       ret = drm_prime_add_imported_buf_handle(&file_priv->prime,
+       ret = drm_prime_add_buf_handle(&file_priv->prime,
                        dma_buf, *handle);
        if (ret)
                goto fail;
@@ -487,7 +490,7 @@ 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)
 {
        struct drm_prime_member *member;
 
@@ -495,14 +498,14 @@ 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;
        list_add(&member->entry, &prime_fpriv->head);
        return 0;
 }
-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)
+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;
 
@@ -514,19 +517,20 @@ 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..f1ce786 100644 (file)
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -1593,9 +1593,8 @@ 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,