rcutorture: Print time since GP end upon forward-progress failure

If rcutorture's forward-progress tests fail while a grace period is not
in progress, it is useful to print the time since the last grace period
ended as a way to detect failure to launch a new grace period.  This
commit therefore makes this change.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

2 files changed, 6 insertions, 1 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f91631541965..9180158756d2 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2000,7 +2000,8 @@ static void rcu_gp_cleanup(void)
 
         WRITE_ONCE(rcu_state.gp_activity, jiffies);
         raw_spin_lock_irq_rcu_node(rnp);
-        gp_duration = jiffies - rcu_state.gp_start;
+        rcu_state.gp_end = jiffies;
+        gp_duration = rcu_state.gp_end - rcu_state.gp_start;
         if (gp_duration > rcu_state.gp_max)
                 rcu_state.gp_max = gp_duration;
 
@@ -2686,6 +2687,8 @@ void rcu_fwd_progress_check(unsigned long j)
                         __func__, jiffies - rcu_state.gp_start);
                 show_rcu_gp_kthreads();
         } else {
+                pr_info("%s: Last GP end %lu jiffies ago\n",
+                        __func__, jiffies - rcu_state.gp_end);
                 preempt_disable();
                 rdp = this_cpu_ptr(&rcu_data);
                 rcu_check_gp_start_stall(rdp->mynode, rdp, j);
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index a8f82b7dc5e2..d90b02b53c0e 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -328,6 +328,8 @@ struct rcu_state {
                                                 /*  force_quiescent_state(). */
         unsigned long gp_start;                 /* Time at which GP started, */
                                                 /*  but in jiffies. */
+        unsigned long gp_end;                   /* Time last GP ended, again */
+                                                /*  in jiffies. */
         unsigned long gp_activity;              /* Time of last GP kthread */
                                                 /*  activity in jiffies. */
         unsigned long gp_req_activity;          /* Time of last GP request */