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@vmware.com Reviewed-by: Roland Scheidegger sroland@vmware.com Fixes: d1a73c641afd ("drm/vmwgfx: Make sure we unpin no longer needed buffers") Cc: dri-devel@lists.freedesktop.org Signed-off-by: Zack Rusin zackr@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);
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