drm/udl: Get rid of dev->struct_mutex usage

It's only used to protect our page list, and only when we know we have
a full reference. This means none of these code paths can ever race
with the final unref, and hence we do not need dev->struct_mutex
serialization and can simply switch to our own locking.

For more context the only magic the locked gem_free_object provides is
that it prevents concurrent final unref (and destruction) of gem
objects while anyone is holding dev->struct_mutex. This was used by
i915 (and other drivers) to implement eviction handling with less
headaches.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180327082356.24516-3-daniel.vetter@ffwll.ch

diff --git a/drivers/gpu/drm/udl/udl_dmabuf.c b/drivers/gpu/drm/udl/udl_dmabuf.c
index 2867ed1..0a20695 100644 (file)
--- a/drivers/gpu/drm/udl/udl_dmabuf.c
+++ b/drivers/gpu/drm/udl/udl_dmabuf.c
@@ -76,6 +76,7 @@ static struct sg_table *udl_map_dma_buf(struct dma_buf_attachment *attach,
        struct udl_drm_dmabuf_attachment *udl_attach = attach->priv;
        struct udl_gem_object *obj = to_udl_bo(attach->dmabuf->priv);
        struct drm_device *dev = obj->base.dev;
+       struct udl_device *udl = dev->dev_private;
        struct scatterlist *rd, *wr;
        struct sg_table *sgt = NULL;
        unsigned int i;
@@ -112,7 +113,7 @@ static struct sg_table *udl_map_dma_buf(struct dma_buf_attachment *attach,
                return ERR_PTR(-ENOMEM);
        }
 
-       mutex_lock(&dev->struct_mutex);
+       mutex_lock(&udl->gem_lock);
 
        rd = obj->sg->sgl;
        wr = sgt->sgl;
@@ -137,7 +138,7 @@ static struct sg_table *udl_map_dma_buf(struct dma_buf_attachment *attach,
        attach->priv = udl_attach;
 
 err_unlock:
-       mutex_unlock(&dev->struct_mutex);
+       mutex_unlock(&udl->gem_lock);
        return sgt;
 }
 

diff --git a/drivers/gpu/drm/udl/udl_drv.c b/drivers/gpu/drm/udl/udl_drv.c
index 3c45a30..9ef515d 100644 (file)
--- a/drivers/gpu/drm/udl/udl_drv.c
+++ b/drivers/gpu/drm/udl/udl_drv.c
@@ -53,7 +53,7 @@ static struct drm_driver driver = {
        .unload = udl_driver_unload,
 
        /* gem hooks */
-       .gem_free_object = udl_gem_free_object,
+       .gem_free_object_unlocked = udl_gem_free_object,
        .gem_vm_ops = &udl_gem_vm_ops,
 
        .dumb_create = udl_dumb_create,

diff --git a/drivers/gpu/drm/udl/udl_drv.h b/drivers/gpu/drm/udl/udl_drv.h
index 2a75ab8..55c0cc3 100644 (file)
--- a/drivers/gpu/drm/udl/udl_drv.h
+++ b/drivers/gpu/drm/udl/udl_drv.h
@@ -54,6 +54,8 @@ struct udl_device {
        struct usb_device *udev;
        struct drm_crtc *crtc;
 
+       struct mutex gem_lock;
+
        int sku_pixel_limit;
 
        struct urb_list urbs;

diff --git a/drivers/gpu/drm/udl/udl_gem.c b/drivers/gpu/drm/udl/udl_gem.c
index dee6bd9..9a15cce 100644 (file)
--- a/drivers/gpu/drm/udl/udl_gem.c
+++ b/drivers/gpu/drm/udl/udl_gem.c
@@ -214,9 +214,10 @@ int udl_gem_mmap(struct drm_file *file, struct drm_device *dev,
 {
        struct udl_gem_object *gobj;
        struct drm_gem_object *obj;
+       struct udl_device *udl = dev->dev_private;
        int ret = 0;
 
-       mutex_lock(&dev->struct_mutex);
+       mutex_lock(&udl->gem_lock);
        obj = drm_gem_object_lookup(file, handle);
        if (obj == NULL) {
                ret = -ENOENT;
@@ -236,6 +237,6 @@ int udl_gem_mmap(struct drm_file *file, struct drm_device *dev,
 out:
        drm_gem_object_put(&gobj->base);
 unlock:
-       mutex_unlock(&dev->struct_mutex);
+       mutex_unlock(&udl->gem_lock);
        return ret;
 }

diff --git a/drivers/gpu/drm/udl/udl_main.c b/drivers/gpu/drm/udl/udl_main.c
index f1ec452..d518de8 100644 (file)
--- a/drivers/gpu/drm/udl/udl_main.c
+++ b/drivers/gpu/drm/udl/udl_main.c
@@ -324,6 +324,8 @@ int udl_driver_load(struct drm_device *dev, unsigned long flags)
        udl->ddev = dev;
        dev->dev_private = udl;
 
+       mutex_init(&udl->gem_lock);
+
        if (!udl_parse_vendor_descriptor(dev, udl->udev)) {
                ret = -ENODEV;
                DRM_ERROR("firmware not recognized. Assume incompatible device\n");