drm/amd/amdkfd: Fix a resource leak in svm_range_validate_and_map()

Analysis of code by Coverity, a static code analyser, has identified
a resource leak in the symbol hmm_range. This leak occurs when one of
the prior steps before it is released encounters an error.
Signed-off-by: Ramesh Errabolu <Ramesh.Errabolu@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdkfd/kfd_svm.c

@@ -1670,7 +1670,7 @@ static int svm_range_validate_and_map(struct mm_struct *mm,
 	start = map_start << PAGE_SHIFT;
 	end = (map_last + 1) << PAGE_SHIFT;
 	for (addr = start; !r && addr < end; ) {
-		struct hmm_range *hmm_range;
+		struct hmm_range *hmm_range = NULL;
 		unsigned long map_start_vma;
 		unsigned long map_last_vma;
 		struct vm_area_struct *vma;
@@ -1705,7 +1705,12 @@ static int svm_range_validate_and_map(struct mm_struct *mm,
 		}
 
 		svm_range_lock(prange);
-		if (!r && amdgpu_hmm_range_get_pages_done(hmm_range)) {
+
+		/* Free backing memory of hmm_range if it was initialized
+		 * Overrride return value to TRY AGAIN only if prior returns
+		 * were successful
+		 */
+		if (hmm_range && amdgpu_hmm_range_get_pages_done(hmm_range) && !r) {
 			pr_debug("hmm update the range, need validate again\n");
 			r = -EAGAIN;
 		}