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>

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 5aab7da..ff21411 100644 (file)
--- 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();