[PATCH printk v5 29/30] rcu: Mark emergency sections in rcu stalls

John Ogness
2024-05-02T21:38:57Z

Mark emergency sections wherever multiple lines of
rcu stall information are generated. In an emergency
section the CPU will not perform console output for the
printk() calls. Instead, a flushing of the console
output is triggered when exiting the emergency section.
This allows the full message block to be stored as
quickly as possible in the ringbuffer.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
kernel/rcu/tree_exp.h | 9 +++++++++
kernel/rcu/tree_stall.h | 11 +++++++++++
2 files changed, 20 insertions(+)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 6b83537480b1..bc1d8733c08f 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -7,6 +7,7 @@
* Authors: Paul E. McKenney <paulmck@linux.ibm.com>
*/

+#include <linux/console.h>
#include <linux/lockdep.h>

static void rcu_exp_handler(void *unused);
@@ -571,6 +572,9 @@ 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"));
@@ -612,6 +616,7 @@ static void synchronize_rcu_expedited_wait(void)
}
pr_cont("\n");
}
+ nbcon_cpu_emergency_flush();
rcu_for_each_leaf_node(rnp) {
for_each_leaf_node_possible_cpu(rnp, cpu) {
mask = leaf_node_cpu_bit(rnp, cpu);
@@ -624,6 +629,9 @@ 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();
}
}
@@ -792,6 +800,7 @@ static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
*/
touch_nmi_watchdog();
sched_show_task(t);
+ nbcon_cpu_emergency_flush();
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 5d666428546b..1ca0826545c1 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -7,6 +7,7 @@
* Author: Paul E. McKenney <paulmck@linux.ibm.com>
*/

+#include <linux/console.h>
#include <linux/kvm_para.h>
#include <linux/rcu_notifier.h>

@@ -260,6 +261,7 @@ static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
*/
touch_nmi_watchdog();
sched_show_task(t);
+ nbcon_cpu_emergency_flush();
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
@@ -522,6 +524,7 @@ static void print_cpu_stall_info(int cpu)
falsepositive ? " (false positive?)" : "");

print_cpu_stat_info(cpu);
+ nbcon_cpu_emergency_flush();
}

/* Complain about starvation of grace-period kthread. */
@@ -604,6 +607,8 @@ 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
@@ -655,6 +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. */
@@ -675,6 +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
@@ -703,6 +712,8 @@ 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();

/*
--
2.39.2