1 files changed, 20 insertions, 0 deletions

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index e1e0fcd99613..c75eedd55af5 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -284,6 +284,26 @@ struct held_lock {
  */
 struct hist_lock {
         /*
+         * Id for each entry in the ring buffer. This is used to
+         * decide whether the ring buffer was overwritten or not.
+         *
+         * For example,
+         *
+         *           |<----------- hist_lock ring buffer size ------->|
+         *           pppppppppppppppppppppiiiiiiiiiiiiiiiiiiiiiiiiiiiii
+         * wrapped > iiiiiiiiiiiiiiiiiiiiiiiiiii.......................
+         *
+         *           where 'p' represents an acquisition in process
+         *           context, 'i' represents an acquisition in irq
+         *           context.
+         *
+         * In this example, the ring buffer was overwritten by
+         * acquisitions in irq context, that should be detected on
+         * rollback or commit.
+         */
+        unsigned int hist_id;
+
+        /*
          * Seperate stack_trace data. This will be used at commit step.
          */
         struct stack_trace      trace;