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

[Daniel Vetter]

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.

Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
Cc: Rob Clark <robdclark at gmail.com>
Cc: Sean Paul <sean at poorly.run>
Cc: linux-arm-msm at vger.kernel.org
Cc: freedreno at lists.freedesktop.org
---
 drivers/gpu/drm/msm/msm_gem_submit.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
index fb1fdd7fa3ef..385d4965a8d0 100644
--- 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:
-- 
2.24.0