rcu: Print scheduling-clock information on RCU CPU stall-warning messages

There have been situations where RCU CPU stall warnings were caused by
issues in scheduling-clock timer initialization.  To make it easier to
track these down, this commit causes the RCU CPU stall-warning messages
to print out the number of scheduling-clock interrupts taken in the
current grace period for each stalled CPU.

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

1 files changed, 22 insertions, 11 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index cfdab9898e33..dccd2f78db4e 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -689,12 +689,6 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
                 return;
         }
         rsp->jiffies_stall = jiffies + 3 * jiffies_till_stall_check() + 3;
-
-        /*
-         * Now rat on any tasks that got kicked up to the root rcu_node
-         * due to CPU offlining.
-         */
-        ndetected = rcu_print_task_stall(rnp);
         raw_spin_unlock_irqrestore(&rnp->lock, flags);
 
         /*
@@ -702,8 +696,9 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
          * See Documentation/RCU/stallwarn.txt for info on how to debug
          * RCU CPU stall warnings.
          */
-        printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks: {",
+        printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks:",
                rsp->name);
+        print_cpu_stall_info_begin();
         rcu_for_each_leaf_node(rsp, rnp) {
                 raw_spin_lock_irqsave(&rnp->lock, flags);
                 ndetected += rcu_print_task_stall(rnp);
@@ -712,11 +707,22 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
                         continue;
                 for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
                         if (rnp->qsmask & (1UL << cpu)) {
-                                printk(" %d", rnp->grplo + cpu);
+                                print_cpu_stall_info(rsp, rnp->grplo + cpu);
                                 ndetected++;
                         }
         }
-        printk("} (detected by %d, t=%ld jiffies)\n",
+
+        /*
+         * Now rat on any tasks that got kicked up to the root rcu_node
+         * due to CPU offlining.
+         */
+        rnp = rcu_get_root(rsp);
+        raw_spin_lock_irqsave(&rnp->lock, flags);
+        ndetected = rcu_print_task_stall(rnp);
+        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+
+        print_cpu_stall_info_end();
+        printk(KERN_CONT "(detected by %d, t=%ld jiffies)\n",
                smp_processor_id(), (long)(jiffies - rsp->gp_start));
         if (ndetected == 0)
                 printk(KERN_ERR "INFO: Stall ended before state dump start\n");
@@ -740,8 +746,11 @@ static void print_cpu_stall(struct rcu_state *rsp)
          * See Documentation/RCU/stallwarn.txt for info on how to debug
          * RCU CPU stall warnings.
          */
-        printk(KERN_ERR "INFO: %s detected stall on CPU %d (t=%lu jiffies)\n",
-               rsp->name, smp_processor_id(), jiffies - rsp->gp_start);
+        printk(KERN_ERR "INFO: %s self-detected stall on CPU", rsp->name);
+        print_cpu_stall_info_begin();
+        print_cpu_stall_info(rsp, smp_processor_id());
+        print_cpu_stall_info_end();
+        printk(KERN_CONT " (t=%lu jiffies)\n", jiffies - rsp->gp_start);
         if (!trigger_all_cpu_backtrace())
                 dump_stack();
 
@@ -831,6 +840,7 @@ static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct
                         rdp->passed_quiesce = 0;
                 } else
                         rdp->qs_pending = 0;
+                zero_cpu_stall_ticks(rdp);
         }
 }
 
@@ -1496,6 +1506,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
 void rcu_check_callbacks(int cpu, int user)
 {
         trace_rcu_utilization("Start scheduler-tick");
+        increment_cpu_stall_ticks();
         if (user || rcu_is_cpu_rrupt_from_idle()) {
 
                 /*