From: John Ogness Date: Mon, 11 Sep 2023 15:53:39 +0000 Subject: [PATCH 28/46] rcu: Mark emergency sections in rcu stalls Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.9/older/patches-6.9-rt5.tar.xz 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 Signed-off-by: Sebastian Andrzej Siewior --- kernel/rcu/tree_exp.h | 9 +++++++++ kernel/rcu/tree_stall.h | 11 +++++++++++ 2 files changed, 20 insertions(+) --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -7,6 +7,7 @@ * Authors: Paul E. McKenney */ +#include #include static void rcu_exp_handler(void *unused); @@ -571,6 +572,9 @@ static void synchronize_rcu_expedited_wa 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_wa } 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_wa 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_st */ touch_nmi_watchdog(); sched_show_task(t); + nbcon_cpu_emergency_flush(); } raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -7,6 +7,7 @@ * Author: Paul E. McKenney */ +#include #include #include @@ -260,6 +261,7 @@ static void rcu_print_detail_task_stall_ */ 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(unsign 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(unsign 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 lon 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 lon jiffies + 3 * rcu_jiffies_till_stall_check() + 3); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + nbcon_cpu_emergency_exit(); + panic_on_rcu_stall(); /*