drm/msm: Don't init ww_mutec acquire ctx before needed

For locking semantics it really doesn't matter when we grab the
ticket. But for lockdep validation it does: the acquire ctx is a fake
lockdep. Since other drivers might want to do a full multi-lock dance
in their fault-handler, not just lock a single dma_resv. Therefore we
must init the acquire_ctx only after we've done all the copy_*_user or
anything else that might trigger a pagefault. For msm this means we
need to move it past submit_lookup_objects.

Aside: Why is msm still using struct_mutex, it seems to be using
dma_resv_lock for general buffer state protection?

v2:
- Add comment to explain why the ww ticket setup is separate (Rob)
- Fix up error handling, we need to make sure we don't call
  ww_acquire_fini without _init.

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-and-tested-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Sean Paul <sean@poorly.run>
Cc: linux-arm-msm@vger.kernel.org
Cc: freedreno@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20191120105607.3023-1-daniel.vetter@ffwll.ch

diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
index be5327a..7d04c47 100644 (file)
--- a/drivers/gpu/drm/msm/msm_gem_submit.c
+++ b/drivers/gpu/drm/msm/msm_gem_submit.c
@@ -54,7 +54,6 @@ static struct msm_gem_submit *submit_create(struct drm_device *dev,
 
        INIT_LIST_HEAD(&submit->node);
        INIT_LIST_HEAD(&submit->bo_list);
-       ww_acquire_init(&submit->ticket, &reservation_ww_class);
 
        return submit;
 }
@@ -390,8 +389,6 @@ static void submit_cleanup(struct msm_gem_submit *submit)
                list_del_init(&msm_obj->submit_entry);
                drm_gem_object_put(&msm_obj->base);
        }
-
-       ww_acquire_fini(&submit->ticket);
 }
 
 int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
@@ -408,6 +405,7 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
        struct msm_ringbuffer *ring;
        int out_fence_fd = -1;
        struct pid *pid = get_pid(task_pid(current));
+       bool has_ww_ticket = false;
        unsigned i;
        int ret, submitid;
        if (!gpu)
@@ -489,6 +487,9 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
        if (ret)
                goto out;
 
+       /* copy_*_user while holding a ww ticket upsets lockdep */
+       ww_acquire_init(&submit->ticket, &reservation_ww_class);
+       has_ww_ticket = true;
        ret = submit_lock_objects(submit);
        if (ret)
                goto out;
@@ -588,6 +589,8 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
 
 out:
        submit_cleanup(submit);
+       if (has_ww_ticket)
+               ww_acquire_fini(&submit->ticket);
        if (ret)
                msm_gem_submit_free(submit);
 out_unlock: