[PATCH v4] drm/amdgpu: Fix the race condition for draining retry fault

[Emily Deng <Emily.Deng@amd.com>]

Issue:
In the scenario where svm_range_restore_pages is called, but svm->checkpoint_ts
 has not been set and the retry fault has not been drained, svm_range_unmap_from_cpu
is triggered and calls svm_range_free. Meanwhile, svm_range_restore_pages
continues execution and reaches svm_range_from_addr. This results in
a "failed to find prange..." error, causing the page recovery to fail.

How to fix:
Move the timestamp check code under the protection of svm->lock.

v2:
Make sure all right locks are released before go out.

v3:
Directly goto out_unlock_svms, and return -EAGAIN.

v4:
Refine code.

Signed-off-by: Emily Deng <Emily.Deng@amd.com>
---
 drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 30 +++++++++++++++-------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
index d04725583f19..83ac14bf7a7a 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
@@ -3008,19 +3008,6 @@ svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,
 		goto out;
 	}
 
-	/* check if this page fault time stamp is before svms->checkpoint_ts */
-	if (svms->checkpoint_ts[gpuidx] != 0) {
-		if (amdgpu_ih_ts_after_or_equal(ts,  svms->checkpoint_ts[gpuidx])) {
-			pr_debug("draining retry fault, drop fault 0x%llx\n", addr);
-			r = 0;
-			goto out;
-		} else
-			/* ts is after svms->checkpoint_ts now, reset svms->checkpoint_ts
-			 * to zero to avoid following ts wrap around give wrong comparing
-			 */
-			svms->checkpoint_ts[gpuidx] = 0;
-	}
-
 	if (!p->xnack_enabled) {
 		pr_debug("XNACK not enabled for pasid 0x%x\n", pasid);
 		r = -EFAULT;
@@ -3040,6 +3027,20 @@ svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,
 	mmap_read_lock(mm);
 retry_write_locked:
 	mutex_lock(&svms->lock);
+
+	/* check if this page fault time stamp is before svms->checkpoint_ts */
+	if (svms->checkpoint_ts[gpuidx] != 0) {
+		if (amdgpu_ih_ts_after_or_equal(ts,  svms->checkpoint_ts[gpuidx])) {
+			pr_debug("draining retry fault, drop fault 0x%llx\n", addr);
+			r = -EAGAIN;
+			goto out_unlock_svms;
+		} else
+			/* ts is after svms->checkpoint_ts now, reset svms->checkpoint_ts
+			 * to zero to avoid following ts wrap around give wrong comparing
+			 */
+			svms->checkpoint_ts[gpuidx] = 0;
+	}
+
 	prange = svm_range_from_addr(svms, addr, NULL);
 	if (!prange) {
 		pr_debug("failed to find prange svms 0x%p address [0x%llx]\n",
@@ -3165,7 +3166,8 @@ svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,
 	mutex_unlock(&svms->lock);
 	mmap_read_unlock(mm);
 
-	svm_range_count_fault(node, p, gpuidx);
+	if (r != -EAGAIN)
+		svm_range_count_fault(node, p, gpuidx);
 
 	mmput(mm);
 out:
-- 
2.34.1