2 files changed, 75 insertions, 1 deletions
diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index ba2e0f1940bd..8e36d8695f81 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -182,6 +182,7 @@ static inline void printk_get_console_flush_type(struct console_flush_type *ft)
 
 	switch (nbcon_get_default_prio()) {
 	case NBCON_PRIO_NORMAL:
+	case NBCON_PRIO_EMERGENCY:
 		if (have_nbcon_console && !have_boot_console)
 			ft->nbcon_atomic = true;
 
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index 18488d6c17c0..92ac5c590927 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -972,6 +972,36 @@ update_con:
 	return nbcon_context_exit_unsafe(ctxt);
 }
 
+/* Track the nbcon emergency nesting per CPU. */
+static DEFINE_PER_CPU(unsigned int, nbcon_pcpu_emergency_nesting);
+static unsigned int early_nbcon_pcpu_emergency_nesting __initdata;
+
+/**
+ * nbcon_get_cpu_emergency_nesting - Get the per CPU emergency nesting pointer
+ *
+ * Context:	For reading, any context. For writing, any context which could
+ *		not be migrated to another CPU.
+ * Return:	Either a pointer to the per CPU emergency nesting counter of
+ *		the current CPU or to the init data during early boot.
+ *
+ * The function is safe for reading per-CPU variables in any context because
+ * preemption is disabled if the current CPU is in the emergency state. See
+ * also nbcon_cpu_emergency_enter().
+ */
+static __ref unsigned int *nbcon_get_cpu_emergency_nesting(void)
+{
+	/*
+	 * The value of __printk_percpu_data_ready gets set in normal
+	 * context and before SMP initialization. As a result it could
+	 * never change while inside an nbcon emergency section.
+	 */
+	if (!printk_percpu_data_ready())
+		return &early_nbcon_pcpu_emergency_nesting;
+
+	/* Open code this_cpu_ptr() without checking migration. */
+	return per_cpu_ptr(&nbcon_pcpu_emergency_nesting, raw_smp_processor_id());
+}
+
 /**
  * nbcon_get_default_prio - The appropriate nbcon priority to use for nbcon
  *				printing on the current CPU
@@ -981,13 +1011,20 @@ update_con:
  *		context for printing.
  *
  * The function is safe for reading per-CPU data in any context because
- * preemption is disabled if the current CPU is in the panic state.
+ * preemption is disabled if the current CPU is in the emergency or panic
+ * state.
  */
 enum nbcon_prio nbcon_get_default_prio(void)
 {
+	unsigned int *cpu_emergency_nesting;
+
 	if (this_cpu_in_panic())
 		return NBCON_PRIO_PANIC;
 
+	cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting();
+	if (*cpu_emergency_nesting)
+		return NBCON_PRIO_EMERGENCY;
+
 	return NBCON_PRIO_NORMAL;
 }
 
@@ -1247,6 +1284,42 @@ void nbcon_atomic_flush_unsafe(void)
 }
 
 /**
+ * nbcon_cpu_emergency_enter - Enter an emergency section where printk()
+ *				messages for that CPU are flushed directly
+ *
+ * Context:	Any context. Disables preemption.
+ *
+ * When within an emergency section, printk() calls will attempt to flush any
+ * pending messages in the ringbuffer.
+ */
+void nbcon_cpu_emergency_enter(void)
+{
+	unsigned int *cpu_emergency_nesting;
+
+	preempt_disable();
+
+	cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting();
+	(*cpu_emergency_nesting)++;
+}
+
+/**
+ * nbcon_cpu_emergency_exit - Exit an emergency section
+ *
+ * Context:	Within an emergency section. Enables preemption.
+ */
+void nbcon_cpu_emergency_exit(void)
+{
+	unsigned int *cpu_emergency_nesting;
+
+	cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting();
+
+	if (!WARN_ON_ONCE(*cpu_emergency_nesting == 0))
+		(*cpu_emergency_nesting)--;
+
+	preempt_enable();
+}
+
+/**
  * nbcon_alloc - Allocate and init the nbcon console specific data
  * @con:	Console to initialize
  *