Fix abd_get_offset_struct() may allocate new abd

Even when supplied with an abd to abd_get_offset_struct(), the call
to abd_get_offset_impl() can allocate a different abd. Ensure to
call abd_fini_struct() on the abd that is not used.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Jorgen Lundman <[email protected]>
Closes #11683

Author: lundman

module/zfs/abd.c

@@ -555,8 +555,12 @@ abd_get_offset_impl(abd_t *abd, abd_t *sabd, size_t off, size_t size)
 abd_t *
 abd_get_offset_struct(abd_t *abd, abd_t *sabd, size_t off, size_t size)
 {
+	abd_t *result;
 	abd_init_struct(abd);
-	return (abd_get_offset_impl(abd, sabd, off, size));
+	result = abd_get_offset_impl(abd, sabd, off, size);
+	if (result != abd)
+		abd_fini_struct(abd);
+	return (result);
 }
 
 abd_t *