rcu: Add failure tracing to rcutorture

Trace the rcutorture RCU accesses and dump the trace buffer when the
first failure is detected.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

include/linux/rcupdate.h

@@ -51,13 +51,21 @@ extern int rcutorture_runnable; /* for sysctl */
 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
 extern void rcutorture_record_test_transition(void);
 extern void rcutorture_record_progress(unsigned long vernum);
+extern void do_trace_rcu_torture_read(char *rcutorturename,
+				      struct rcu_head *rhp);
 #else
 static inline void rcutorture_record_test_transition(void)
 {
 }
 static inline void rcutorture_record_progress(unsigned long vernum)
 {
 }
+#ifdef CONFIG_RCU_TRACE
+extern void do_trace_rcu_torture_read(char *rcutorturename,
+				      struct rcu_head *rhp);
+#else
+#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
+#endif
 #endif
 
 #define UINT_CMP_GE(a, b)	(UINT_MAX / 2 >= (a) - (b))

include/trace/events/rcu.h

@@ -437,6 +437,31 @@ TRACE_EVENT(rcu_batch_end,
 		  __entry->rcuname, __entry->callbacks_invoked)
 );
 
+/*
+ * Tracepoint for rcutorture readers.  The first argument is the name
+ * of the RCU flavor from rcutorture's viewpoint and the second argument
+ * is the callback address.
+ */
+TRACE_EVENT(rcu_torture_read,
+
+	TP_PROTO(char *rcutorturename, struct rcu_head *rhp),
+
+	TP_ARGS(rcutorturename, rhp),
+
+	TP_STRUCT__entry(
+		__field(char *, rcutorturename)
+		__field(struct rcu_head *, rhp)
+	),
+
+	TP_fast_assign(
+		__entry->rcutorturename = rcutorturename;
+		__entry->rhp = rhp;
+	),
+
+	TP_printk("%s torture read %p",
+		  __entry->rcutorturename, __entry->rhp)
+);
+
 #else /* #ifdef CONFIG_RCU_TRACE */
 
 #define trace_rcu_grace_period(rcuname, gpnum, gpevent) do { } while (0)
@@ -452,6 +477,7 @@ TRACE_EVENT(rcu_batch_end,
 #define trace_rcu_invoke_callback(rcuname, rhp) do { } while (0)
 #define trace_rcu_invoke_kfree_callback(rcuname, rhp, offset) do { } while (0)
 #define trace_rcu_batch_end(rcuname, callbacks_invoked) do { } while (0)
+#define trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
 
 #endif /* #else #ifdef CONFIG_RCU_TRACE */
 

kernel/rcupdate.c

@@ -316,3 +316,13 @@ struct debug_obj_descr rcuhead_debug_descr = {
 };
 EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
+
+#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
+void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp)
+{
+	trace_rcu_torture_read(rcutorturename, rhp);
+}
+EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
+#else
+#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
+#endif

kernel/rcutorture.c

@@ -913,6 +913,18 @@ rcu_torture_fakewriter(void *arg)
 	return 0;
 }
 
+void rcutorture_trace_dump(void)
+{
+	static atomic_t beenhere = ATOMIC_INIT(0);
+
+	if (atomic_read(&beenhere))
+		return;
+	if (atomic_xchg(&beenhere, 1) != 0)
+		return;
+	do_trace_rcu_torture_read(cur_ops->name, (struct rcu_head *)~0UL);
+	ftrace_dump(DUMP_ALL);
+}
+
 /*
  * RCU torture reader from timer handler.  Dereferences rcu_torture_current,
  * incrementing the corresponding element of the pipeline array.  The
@@ -934,6 +946,7 @@ static void rcu_torture_timer(unsigned long unused)
 				  rcu_read_lock_bh_held() ||
 				  rcu_read_lock_sched_held() ||
 				  srcu_read_lock_held(&srcu_ctl));
+	do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu);
 	if (p == NULL) {
 		/* Leave because rcu_torture_writer is not yet underway */
 		cur_ops->readunlock(idx);
@@ -951,6 +964,8 @@ static void rcu_torture_timer(unsigned long unused)
 		/* Should not happen, but... */
 		pipe_count = RCU_TORTURE_PIPE_LEN;
 	}
+	if (pipe_count > 1)
+		rcutorture_trace_dump();
 	__this_cpu_inc(rcu_torture_count[pipe_count]);
 	completed = cur_ops->completed() - completed;
 	if (completed > RCU_TORTURE_PIPE_LEN) {
@@ -994,6 +1009,7 @@ rcu_torture_reader(void *arg)
 					  rcu_read_lock_bh_held() ||
 					  rcu_read_lock_sched_held() ||
 					  srcu_read_lock_held(&srcu_ctl));
+		do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu);
 		if (p == NULL) {
 			/* Wait for rcu_torture_writer to get underway */
 			cur_ops->readunlock(idx);
@@ -1009,6 +1025,8 @@ rcu_torture_reader(void *arg)
 			/* Should not happen, but... */
 			pipe_count = RCU_TORTURE_PIPE_LEN;
 		}
+		if (pipe_count > 1)
+			rcutorture_trace_dump();
 		__this_cpu_inc(rcu_torture_count[pipe_count]);
 		completed = cur_ops->completed() - completed;
 		if (completed > RCU_TORTURE_PIPE_LEN) {