rcu: Call touch_nmi_watchdog() while printing stall warnings

[ Upstream commit 3caa973b7a260e7a2a69edc94c300ab9c65148c3 ]

When RCU stall warning triggers, it can print out a lot of messages
while holding spinlocks.  If the console device is slow (e.g. an
actual or IPMI serial console), it may end up triggering NMI hard
lockup watchdog like the following.

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index e3944c4b072d93415c3c800b33a081acbf2836da..554ea54e8d61ee3ffdb6a64a8932417bb4ff5134 100644 (file)
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -521,8 +521,14 @@ static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
        }
        t = list_entry(rnp->gp_tasks->prev,
                       struct task_struct, rcu_node_entry);
-       list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
+       list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
+               /*
+                * We could be printing a lot while holding a spinlock.
+                * Avoid triggering hard lockup.
+                */
+               touch_nmi_watchdog();
                sched_show_task(t);
+       }
        raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 }
 
@@ -1629,6 +1635,12 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
        char *ticks_title;
        unsigned long ticks_value;
 
+       /*
+        * We could be printing a lot while holding a spinlock.  Avoid
+        * triggering hard lockup.
+        */
+       touch_nmi_watchdog();
+
        if (rsp->gpnum == rdp->gpnum) {
                ticks_title = "ticks this GP";
                ticks_value = rdp->ticks_this_gp;