[PATCH 2/2] drm/vmwgfx: Make sure unpinning handles reservations

[Zack Rusin]

Quite often it's a little hard to tell if reservations are already held
in code paths that unpin bo's. While our pinning/unpinning code should
be more explicit that requires a substential amount of work so instead
we can avoid the issues by making sure we try to reserve before unpinning.
Because we unpin those bo's only on destruction/error paths just that check
tells us if we're already reserved or not and allows to cleanly unpin.

Reviewed-by: Martin Krastev <krastevm at vmware.com>
Reviewed-by: Roland Scheidegger <sroland at vmware.com>
Fixes: d1a73c641afd ("drm/vmwgfx: Make sure we unpin no longer needed buffers")
Cc: dri-devel at lists.freedesktop.org
Signed-off-by: Zack Rusin <zackr at vmware.com>
---
 drivers/gpu/drm/vmwgfx/vmwgfx_drv.h | 17 ++++++++++++++++-
 drivers/gpu/drm/vmwgfx/vmwgfx_mob.c |  8 ++++----
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
index 8087a9013455..03bef9c17e56 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
@@ -1517,6 +1517,21 @@ static inline struct vmw_surface *vmw_surface_reference(struct vmw_surface *srf)
 	return srf;
 }
 
+/*
+ * vmw_bo_unpin_safe - currently pinning requires a reservation to be held
+ * but sometimes it's hard to tell if we're in a callback whose parent
+ * is already holding a reservation, to avoid deadloacks we have to try
+ * to get a reservation explicitly to also try to avoid messing up the
+ * internal ttm lru bo list
+ */
+static inline void vmw_bo_unpin_safe(struct ttm_buffer_object *bo)
+{
+	bool locked = dma_resv_trylock(bo->base.resv);
+	ttm_bo_unpin(bo);
+	if (locked)
+		dma_resv_unlock(bo->base.resv);
+}
+
 static inline void vmw_bo_unreference(struct vmw_buffer_object **buf)
 {
 	struct vmw_buffer_object *tmp_buf = *buf;
@@ -1524,7 +1539,7 @@ static inline void vmw_bo_unreference(struct vmw_buffer_object **buf)
 	*buf = NULL;
 	if (tmp_buf != NULL) {
 		if (tmp_buf->base.pin_count > 0)
-			ttm_bo_unpin(&tmp_buf->base);
+			vmw_bo_unpin_safe(&tmp_buf->base);
 		ttm_bo_put(&tmp_buf->base);
 	}
 }
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_mob.c b/drivers/gpu/drm/vmwgfx/vmwgfx_mob.c
index a0b53141dded..23ffeb2dd6e0 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_mob.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_mob.c
@@ -277,7 +277,7 @@ static int vmw_otable_batch_setup(struct vmw_private *dev_priv,
 						 &batch->otables[i]);
 	}
 
-	ttm_bo_unpin(batch->otable_bo);
+	vmw_bo_unpin_safe(batch->otable_bo);
 	ttm_bo_put(batch->otable_bo);
 	batch->otable_bo = NULL;
 	return ret;
@@ -343,7 +343,7 @@ static void vmw_otable_batch_takedown(struct vmw_private *dev_priv,
 	vmw_bo_fence_single(bo, NULL);
 	ttm_bo_unreserve(bo);
 
-	ttm_bo_unpin(batch->otable_bo);
+	vmw_bo_unpin_safe(batch->otable_bo);
 	ttm_bo_put(batch->otable_bo);
 	batch->otable_bo = NULL;
 }
@@ -530,7 +530,7 @@ static void vmw_mob_pt_setup(struct vmw_mob *mob,
 void vmw_mob_destroy(struct vmw_mob *mob)
 {
 	if (mob->pt_bo) {
-		ttm_bo_unpin(mob->pt_bo);
+		vmw_bo_unpin_safe(mob->pt_bo);
 		ttm_bo_put(mob->pt_bo);
 		mob->pt_bo = NULL;
 	}
@@ -646,7 +646,7 @@ int vmw_mob_bind(struct vmw_private *dev_priv,
 out_no_cmd_space:
 	vmw_fifo_resource_dec(dev_priv);
 	if (pt_set_up) {
-		ttm_bo_unpin(mob->pt_bo);
+		vmw_bo_unpin_safe(mob->pt_bo);
 		ttm_bo_put(mob->pt_bo);
 		mob->pt_bo = NULL;
 	}
-- 
2.27.0