rcu: Mark emergency sections in rcu stalls

Mark emergency sections wherever multiple lines of
rcu stall information are generated. In an emergency
section, every printk() call will attempt to directly
flush to the consoles using the EMERGENCY priority.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Acked-by: Paul E. McKenney <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

Author: jogness

kernel/rcu/tree_exp.h

@@ -7,6 +7,7 @@
  * Authors: Paul E. McKenney <[email protected]>
  */
 
+#include <linux/console.h>
 #include <linux/lockdep.h>
 
 static void rcu_exp_handler(void *unused);
@@ -590,6 +591,9 @@ static void synchronize_rcu_expedited_wait(void)
 			return;
 		if (rcu_stall_is_suppressed())
 			continue;
+
+		nbcon_cpu_emergency_enter();
+
 		j = jiffies;
 		rcu_stall_notifier_call_chain(RCU_STALL_NOTIFY_EXP, (void *)(j - jiffies_start));
 		trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall"));
@@ -643,6 +647,9 @@ static void synchronize_rcu_expedited_wait(void)
 			rcu_exp_print_detail_task_stall_rnp(rnp);
 		}
 		jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
+
+		nbcon_cpu_emergency_exit();
+
 		panic_on_rcu_stall();
 	}
 }

kernel/rcu/tree_stall.h

@@ -7,6 +7,7 @@
  * Author: Paul E. McKenney <[email protected]>
  */
 
+#include <linux/console.h>
 #include <linux/kvm_para.h>
 #include <linux/rcu_notifier.h>
 
@@ -605,6 +606,8 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 	if (rcu_stall_is_suppressed())
 		return;
 
+	nbcon_cpu_emergency_enter();
+
 	/*
 	 * OK, time to rat on our buddy...
 	 * See Documentation/RCU/stallwarn.rst for info on how to debug
@@ -657,6 +660,8 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 	rcu_check_gp_kthread_expired_fqs_timer();
 	rcu_check_gp_kthread_starvation();
 
+	nbcon_cpu_emergency_exit();
+
 	panic_on_rcu_stall();
 
 	rcu_force_quiescent_state();  /* Kick them all. */
@@ -677,6 +682,8 @@ static void print_cpu_stall(unsigned long gps)
 	if (rcu_stall_is_suppressed())
 		return;
 
+	nbcon_cpu_emergency_enter();
+
 	/*
 	 * OK, time to rat on ourselves...
 	 * See Documentation/RCU/stallwarn.rst for info on how to debug
@@ -706,6 +713,8 @@ static void print_cpu_stall(unsigned long gps)
 			   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 
+	nbcon_cpu_emergency_exit();
+
 	panic_on_rcu_stall();
 
 	/*