Subject: [PATCH 32/48] lockdep: Mark emergency sections in lockdep splats
From: John Ogness <[email-masked]>
Date: Mon, 18 Sep 2023 20:27:41 +0000

Mark emergency sections wherever multiple lines of
lock debugging output 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 <[email-masked]>
Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 kernel/locking/lockdep.c |   91 +++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 88 insertions(+), 3 deletions(-)

Index: linux-6.8.2-rt10/kernel/locking/lockdep.c
===================================================================
--- linux-6.8.2-rt10.orig/kernel/locking/lockdep.c
+++ linux-6.8.2-rt10/kernel/locking/lockdep.c
@@ -56,6 +56,7 @@
 #include <linux/kprobes.h>
 #include <linux/lockdep.h>
 #include <linux/context_tracking.h>
+#include <linux/console.h>
 
 #include <asm/sections.h>
 
@@ -574,8 +575,10 @@ static struct lock_trace *save_trace(voi
 		if (!debug_locks_off_graph_unlock())
 			return NULL;
 
+		nbcon_cpu_emergency_enter();
 		print_lockdep_off("BUG: MAX_STACK_TRACE_ENTRIES too low!");
 		dump_stack();
+		nbcon_cpu_emergency_exit();
 
 		return NULL;
 	}
@@ -782,6 +785,8 @@ static void lockdep_print_held_locks(str
 {
 	int i, depth = READ_ONCE(p->lockdep_depth);
 
+	nbcon_cpu_emergency_enter();
+
 	if (!depth)
 		printk("no locks held by %s/%d.\n", p->comm, task_pid_nr(p));
 	else
@@ -792,11 +797,13 @@ static void lockdep_print_held_locks(str
 	 * and it's not the current task.
 	 */
 	if (p != current && task_is_running(p))
-		return;
+		goto out;
 	for (i = 0; i < depth; i++) {
 		printk(" #%d: ", i);
 		print_lock(p->held_locks + i);
 	}
+out:
+	nbcon_cpu_emergency_exit();
 }
 
 static void print_kernel_ident(void)
@@ -888,11 +895,13 @@ look_up_lock_class(const struct lockdep_
 	if (unlikely(subclass >= MAX_LOCKDEP_SUBCLASSES)) {
 		instrumentation_begin();
 		debug_locks_off();
+		nbcon_cpu_emergency_enter();
 		printk(KERN_ERR
 			"BUG: looking up invalid subclass: %u\n", subclass);
 		printk(KERN_ERR
 			"turning off the locking correctness validator.\n");
 		dump_stack();
+		nbcon_cpu_emergency_exit();
 		instrumentation_end();
 		return NULL;
 	}
@@ -969,11 +978,13 @@ static bool assign_lock_key(struct lockd
 	else {
 		/* Debug-check: all keys must be persistent! */
 		debug_locks_off();
+		nbcon_cpu_emergency_enter();
 		pr_err("INFO: trying to register non-static key.\n");
 		pr_err("The code is fine but needs lockdep annotation, or maybe\n");
 		pr_err("you didn't initialize this object before use?\n");
 		pr_err("turning off the locking correctness validator.\n");
 		dump_stack();
+		nbcon_cpu_emergency_exit();
 		return false;
 	}
 
@@ -1317,8 +1328,10 @@ register_lock_class(struct lockdep_map *
 			return NULL;
 		}
 
+		nbcon_cpu_emergency_enter();
 		print_lockdep_off("BUG: MAX_LOCKDEP_KEYS too low!");
 		dump_stack();
+		nbcon_cpu_emergency_exit();
 		return NULL;
 	}
 	nr_lock_classes++;
@@ -1350,11 +1363,13 @@ register_lock_class(struct lockdep_map *
 	if (verbose(class)) {
 		graph_unlock();
 
+		nbcon_cpu_emergency_enter();
 		printk("\nnew class %px: %s", class->key, class->name);
 		if (class->name_version > 1)
 			printk(KERN_CONT "#%d", class->name_version);
 		printk(KERN_CONT "\n");
 		dump_stack();
+		nbcon_cpu_emergency_exit();
 
 		if (!graph_lock()) {
 			return NULL;
@@ -1393,8 +1408,10 @@ static struct lock_list *alloc_list_entr
 		if (!debug_locks_off_graph_unlock())
 			return NULL;
 
+		nbcon_cpu_emergency_enter();
 		print_lockdep_off("BUG: MAX_LOCKDEP_ENTRIES too low!");
 		dump_stack();
+		nbcon_cpu_emergency_exit();
 		return NULL;
 	}
 	nr_list_entries++;
@@ -2040,6 +2057,8 @@ static noinline void print_circular_bug(
 
 	depth = get_lock_depth(target);
 
+	nbcon_cpu_emergency_enter();
+
 	print_circular_bug_header(target, depth, check_src, check_tgt);
 
 	parent = get_lock_parent(target);
@@ -2058,6 +2077,8 @@ static noinline void print_circular_bug(
 
 	printk("\nstack backtrace:\n");
 	dump_stack();
+
+	nbcon_cpu_emergency_exit();
 }
 
 static noinline void print_bfs_bug(int ret)
@@ -2570,6 +2591,8 @@ print_bad_irq_dependency(struct task_str
 	if (!debug_locks_off_graph_unlock() || debug_locks_silent)
 		return;
 
+	nbcon_cpu_emergency_enter();
+
 	pr_warn("\n");
 	pr_warn("=====================================================\n");
 	pr_warn("WARNING: %s-safe -> %s-unsafe lock order detected\n",
@@ -2619,11 +2642,13 @@ print_bad_irq_dependency(struct task_str
 	pr_warn(" and %s-irq-unsafe lock:\n", irqclass);
 	next_root->trace = save_trace();
 	if (!next_root->trace)
-		return;
+		goto out;
 	print_shortest_lock_dependencies(forwards_entry, next_root);
 
 	pr_warn("\nstack backtrace:\n");
 	dump_stack();
+out:
+	nbcon_cpu_emergency_exit();
 }
 
 static const char *state_names[] = {
@@ -2988,6 +3013,8 @@ print_deadlock_bug(struct task_struct *c
 	if (!debug_locks_off_graph_unlock() || debug_locks_silent)
 		return;
 
+	nbcon_cpu_emergency_enter();
+
 	pr_warn("\n");
 	pr_warn("============================================\n");
 	pr_warn("WARNING: possible recursive locking detected\n");
@@ -3010,6 +3037,8 @@ print_deadlock_bug(struct task_struct *c
 
 	pr_warn("\nstack backtrace:\n");
 	dump_stack();
+
+	nbcon_cpu_emergency_exit();
 }
 
 /*
@@ -3607,6 +3636,8 @@ static void print_collision(struct task_
 			struct held_lock *hlock_next,
 			struct lock_chain *chain)
 {
+	nbcon_cpu_emergency_enter();
+
 	pr_warn("\n");
 	pr_warn("============================\n");
 	pr_warn("WARNING: chain_key collision\n");
@@ -3623,6 +3654,8 @@ static void print_collision(struct task_
 
 	pr_warn("\nstack backtrace:\n");
 	dump_stack();
+
+	nbcon_cpu_emergency_exit();
 }
 #endif
 
@@ -3713,8 +3746,10 @@ static inline int add_chain_cache(struct
 		if (!debug_locks_off_graph_unlock())
 			return 0;
 
+		nbcon_cpu_emergency_enter();
 		print_lockdep_off("BUG: MAX_LOCKDEP_CHAINS too low!");
 		dump_stack();
+		nbcon_cpu_emergency_exit();
 		return 0;
 	}
 	chain->chain_key = chain_key;
@@ -3731,8 +3766,10 @@ static inline int add_chain_cache(struct
 		if (!debug_locks_off_graph_unlock())
 			return 0;
 
+		nbcon_cpu_emergency_enter();
 		print_lockdep_off("BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!");
 		dump_stack();
+		nbcon_cpu_emergency_exit();
 		return 0;
 	}
 
@@ -3971,6 +4008,8 @@ print_usage_bug(struct task_struct *curr
 	if (!debug_locks_off() || debug_locks_silent)
 		return;
 
+	nbcon_cpu_emergency_enter();
+
 	pr_warn("\n");
 	pr_warn("================================\n");
 	pr_warn("WARNING: inconsistent lock state\n");
@@ -3999,6 +4038,8 @@ print_usage_bug(struct task_struct *curr
 
 	pr_warn("\nstack backtrace:\n");
 	dump_stack();
+
+	nbcon_cpu_emergency_exit();
 }
 
 /*
@@ -4033,6 +4074,8 @@ print_irq_inversion_bug(struct task_stru
 	if (!debug_locks_off_graph_unlock() || debug_locks_silent)
 		return;
 
+	nbcon_cpu_emergency_enter();
+
 	pr_warn("\n");
 	pr_warn("========================================================\n");
 	pr_warn("WARNING: possible irq lock inversion dependency detected\n");
@@ -4073,11 +4116,13 @@ print_irq_inversion_bug(struct task_stru
 	pr_warn("\nthe shortest dependencies between 2nd lock and 1st lock:\n");
 	root->trace = save_trace();
 	if (!root->trace)
-		return;
+		goto out;
 	print_shortest_lock_dependencies(other, root);
 
 	pr_warn("\nstack backtrace:\n");
 	dump_stack();
+out:
+	nbcon_cpu_emergency_exit();
 }
 
 /*
@@ -4154,6 +4199,8 @@ void print_irqtrace_events(struct task_s
 {
 	const struct irqtrace_events *trace = &curr->irqtrace;
 
+	nbcon_cpu_emergency_enter();
+
 	printk("irq event stamp: %u\n", trace->irq_events);
 	printk("hardirqs last  enabled at (%u): [<%px>] %pS\n",
 		trace->hardirq_enable_event, (void *)trace->hardirq_enable_ip,
@@ -4167,6 +4214,8 @@ void print_irqtrace_events(struct task_s
 	printk("softirqs last disabled at (%u): [<%px>] %pS\n",
 		trace->softirq_disable_event, (void *)trace->softirq_disable_ip,
 		(void *)trace->softirq_disable_ip);
+
+	nbcon_cpu_emergency_exit();
 }
 
 static int HARDIRQ_verbose(struct lock_class *class)
@@ -4687,10 +4736,12 @@ unlock:
 	 * We must printk outside of the graph_lock:
 	 */
 	if (ret == 2) {
+		nbcon_cpu_emergency_enter();
 		printk("\nmarked lock as {%s}:\n", usage_str[new_bit]);
 		print_lock(this);
 		print_irqtrace_events(curr);
 		dump_stack();
+		nbcon_cpu_emergency_exit();
 	}
 
 	return ret;
@@ -4731,6 +4782,8 @@ print_lock_invalid_wait_context(struct t
 	if (debug_locks_silent)
 		return 0;
 
+	nbcon_cpu_emergency_enter();
+
 	pr_warn("\n");
 	pr_warn("=============================\n");
 	pr_warn("[ BUG: Invalid wait context ]\n");
@@ -4750,6 +4803,8 @@ print_lock_invalid_wait_context(struct t
 	pr_warn("stack backtrace:\n");
 	dump_stack();
 
+	nbcon_cpu_emergency_exit();
+
 	return 0;
 }
 
@@ -4954,6 +5009,8 @@ print_lock_nested_lock_not_held(struct t
 	if (debug_locks_silent)
 		return;
 
+	nbcon_cpu_emergency_enter();
+
 	pr_warn("\n");
 	pr_warn("==================================\n");
 	pr_warn("WARNING: Nested lock was not taken\n");
@@ -4974,6 +5031,8 @@ print_lock_nested_lock_not_held(struct t
 
 	pr_warn("\nstack backtrace:\n");
 	dump_stack();
+
+	nbcon_cpu_emergency_exit();
 }
 
 static int __lock_is_held(const struct lockdep_map *lock, int read);
@@ -5019,11 +5078,13 @@ static int __lock_acquire(struct lockdep
 	debug_class_ops_inc(class);
 
 	if (very_verbose(class)) {
+		nbcon_cpu_emergency_enter();
 		printk("\nacquire class [%px] %s", class->key, class->name);
 		if (class->name_version > 1)
 			printk(KERN_CONT "#%d", class->name_version);
 		printk(KERN_CONT "\n");
 		dump_stack();
+		nbcon_cpu_emergency_exit();
 	}
 
 	/*
@@ -5150,6 +5211,7 @@ static int __lock_acquire(struct lockdep
 #endif
 	if (unlikely(curr->lockdep_depth >= MAX_LOCK_DEPTH)) {
 		debug_locks_off();
+		nbcon_cpu_emergency_enter();
 		print_lockdep_off("BUG: MAX_LOCK_DEPTH too low!");
 		printk(KERN_DEBUG "depth: %i  max: %lu!\n",
 		       curr->lockdep_depth, MAX_LOCK_DEPTH);
@@ -5157,6 +5219,7 @@ static int __lock_acquire(struct lockdep
 		lockdep_print_held_locks(current);
 		debug_show_all_locks();
 		dump_stack();
+		nbcon_cpu_emergency_exit();
 
 		return 0;
 	}
@@ -5176,6 +5239,8 @@ static void print_unlock_imbalance_bug(s
 	if (debug_locks_silent)
 		return;
 
+	nbcon_cpu_emergency_enter();
+
 	pr_warn("\n");
 	pr_warn("=====================================\n");
 	pr_warn("WARNING: bad unlock balance detected!\n");
@@ -5192,6 +5257,8 @@ static void print_unlock_imbalance_bug(s
 
 	pr_warn("\nstack backtrace:\n");
 	dump_stack();
+
+	nbcon_cpu_emergency_exit();
 }
 
 static noinstr int match_held_lock(const struct held_lock *hlock,
@@ -5895,6 +5962,8 @@ static void print_lock_contention_bug(st
 	if (debug_locks_silent)
 		return;
 
+	nbcon_cpu_emergency_enter();
+
 	pr_warn("\n");
 	pr_warn("=================================\n");
 	pr_warn("WARNING: bad contention detected!\n");
@@ -5911,6 +5980,8 @@ static void print_lock_contention_bug(st
 
 	pr_warn("\nstack backtrace:\n");
 	dump_stack();
+
+	nbcon_cpu_emergency_exit();
 }
 
 static void
@@ -6524,6 +6595,8 @@ print_freed_lock_bug(struct task_struct
 	if (debug_locks_silent)
 		return;
 
+	nbcon_cpu_emergency_enter();
+
 	pr_warn("\n");
 	pr_warn("=========================\n");
 	pr_warn("WARNING: held lock freed!\n");
@@ -6536,6 +6609,8 @@ print_freed_lock_bug(struct task_struct
 
 	pr_warn("\nstack backtrace:\n");
 	dump_stack();
+
+	nbcon_cpu_emergency_exit();
 }
 
 static inline int not_in_range(const void* mem_from, unsigned long mem_len,
@@ -6582,6 +6657,8 @@ static void print_held_locks_bug(void)
 	if (debug_locks_silent)
 		return;
 
+	nbcon_cpu_emergency_enter();
+
 	pr_warn("\n");
 	pr_warn("====================================\n");
 	pr_warn("WARNING: %s/%d still has locks held!\n",
@@ -6591,6 +6668,8 @@ static void print_held_locks_bug(void)
 	lockdep_print_held_locks(current);
 	pr_warn("\nstack backtrace:\n");
 	dump_stack();
+
+	nbcon_cpu_emergency_exit();
 }
 
 void debug_check_no_locks_held(void)
@@ -6609,6 +6688,7 @@ void debug_show_all_locks(void)
 		pr_warn("INFO: lockdep is turned off.\n");
 		return;
 	}
+	nbcon_cpu_emergency_enter();
 	pr_warn("\nShowing all locks held in the system:\n");
 
 	rcu_read_lock();
@@ -6623,6 +6703,7 @@ void debug_show_all_locks(void)
 
 	pr_warn("\n");
 	pr_warn("=============================================\n\n");
+	nbcon_cpu_emergency_exit();
 }
 EXPORT_SYMBOL_GPL(debug_show_all_locks);
 #endif
@@ -6648,6 +6729,7 @@ asmlinkage __visible void lockdep_sys_ex
 	if (unlikely(curr->lockdep_depth)) {
 		if (!debug_locks_off())
 			return;
+		nbcon_cpu_emergency_enter();
 		pr_warn("\n");
 		pr_warn("================================================\n");
 		pr_warn("WARNING: lock held when returning to user space!\n");
@@ -6656,6 +6738,7 @@ asmlinkage __visible void lockdep_sys_ex
 		pr_warn("%s/%d is leaving the kernel with locks still held!\n",
 				curr->comm, curr->pid);
 		lockdep_print_held_locks(curr);
+		nbcon_cpu_emergency_exit();
 	}
 
 	/*
@@ -6672,6 +6755,7 @@ void lockdep_rcu_suspicious(const char *
 	bool rcu = warn_rcu_enter();
 
 	/* Note: the following can be executed concurrently, so be careful. */
+	nbcon_cpu_emergency_enter();
 	pr_warn("\n");
 	pr_warn("=============================\n");
 	pr_warn("WARNING: suspicious RCU usage\n");
@@ -6710,6 +6794,7 @@ void lockdep_rcu_suspicious(const char *
 	lockdep_print_held_locks(curr);
 	pr_warn("\nstack backtrace:\n");
 	dump_stack();
+	nbcon_cpu_emergency_exit();
 	warn_rcu_exit(rcu);
 }
 EXPORT_SYMBOL_GPL(lockdep_rcu_suspicious);