drm/i915: Reserve enough fence slot for i915_vma_unbind_async

commit 476fdcdaaae7b06c780cdfc234c704107f16c529 upstream.

A nested dma_resv_reserve_fences(1) will not reserve slot from the
2nd call onwards and folowing dma_resv_add_fence() might hit the
"BUG_ON(fobj->num_fences >= fobj->max_fences)" check.

I915 hit above nested dma_resv case in ttm_bo_handle_move_mem() with
async unbind:

dma_resv_reserve_fences() from --> ttm_bo_handle_move_mem()
        dma_resv_reserve_fences() from --> i915_vma_unbind_async()
        dma_resv_add_fence() from --> i915_vma_unbind_async()
dma_resv_add_fence() from -->ttm_bo_move_accel_cleanup()

Resolve this by adding an extra fence in i915_vma_unbind_async().

Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Fixes: 2f6b90da9192 ("drm/i915: Use vma resources for async unbinding")
Cc: <stable@vger.kernel.org> # v5.18+
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221223092011.11657-1-nirmoy.das@intel.com
(cherry picked from commit 4f0755c2faf7388616109717facc5bbde6850e60)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index 4d06875..c8ad8f3 100644 (file)
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -2114,7 +2114,7 @@ int i915_vma_unbind_async(struct i915_vma *vma, bool trylock_vm)
        if (!obj->mm.rsgt)
                return -EBUSY;
 
-       err = dma_resv_reserve_fences(obj->base.resv, 1);
+       err = dma_resv_reserve_fences(obj->base.resv, 2);
        if (err)
                return -EBUSY;