rcu: refer RCU CPU stall-warning victims to stallwarn.txt

There is some documentation on RCU CPU stall warnings contained in
Documentation/RCU/stallwarn.txt, but it will not be apparent to someone
who runs into such a warning while under time pressure.  This commit
therefore adds comments preceding the printk()s pointing out the
location of this documentation.

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

1 files changed, 10 insertions, 2 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 5aab7dabd0d5..ff214118e4b8 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -487,8 +487,11 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
         rcu_print_task_stall(rnp);
         raw_spin_unlock_irqrestore(&rnp->lock, flags);
 
-        /* OK, time to rat on our buddy... */
-
+        /*
+         * OK, time to rat on our buddy...
+         * 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: {",
                rsp->name);
         rcu_for_each_leaf_node(rsp, rnp) {
@@ -517,6 +520,11 @@ static void print_cpu_stall(struct rcu_state *rsp)
         unsigned long flags;
         struct rcu_node *rnp = rcu_get_root(rsp);
 
+        /*
+         * OK, time to rat on ourselves...
+         * 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);
         trigger_all_cpu_backtrace();