[RFC PATCH 1/2] drm/amdgpu: Move dma_resv waiting outside the notifier lock

[Thomas Hellström]

While the range notifier is executing, we have the write-side mmu interval
seqlock, and mmu_interval_read_retry() is always returning true,
which means that if amdgpu_cs_submit grabs the notifier lock during the
fence wait, it will retry anyway when checking the userptr validity
and block when retrying in mmu_interval_read_begin().
(See the extensive comments in mmu_interval_read_begin())

Hence we can release the notifier lock before the fence wait and avoid
a device-wide command submission block during invalidation.

Cc: Christian König <christian.koenig at amd.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c
index 4b153daf283d..d3d340a6129c 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c
@@ -75,9 +75,10 @@ static bool amdgpu_mn_invalidate_gfx(struct mmu_interval_notifier *mni,
 
 	mmu_interval_set_seq(mni, cur_seq);
 
+	mutex_unlock(&adev->notifier_lock);
+
 	r = dma_resv_wait_timeout(bo->tbo.base.resv, true, false,
 				  MAX_SCHEDULE_TIMEOUT);
-	mutex_unlock(&adev->notifier_lock);
 	if (r <= 0)
 		DRM_ERROR("(%ld) failed to wait for user bo\n", r);
 	return true;
-- 
2.31.1