On 4/9/21 3:38 AM, Thomas Hellström (Intel) wrote:
Hi, Zack,
On 4/8/21 7:22 PM, Zack Rusin wrote:
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@xxxxxxxxxx>
Reviewed-by: Roland Scheidegger <sroland@xxxxxxxxxx>
Fixes: d1a73c641afd ("drm/vmwgfx: Make sure we unpin no longer needed
buffers")
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Zack Rusin <zackr@xxxxxxxxxx>
---
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);
Isn't there a chance another thread is holding the lock and releasing it
at this position?
Yes, it was definitely possible. In v2 I implemented it the way Daniel
suggested, I think it's a decent compromise. Thanks for taking a look at
this!
z
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