Merge branch 'rework/optimizations' into for-linus

kernel/printk/internal.h

@@ -64,6 +64,7 @@ struct dev_printk_info;
 
 extern struct printk_ringbuffer *prb;
 extern bool printk_kthreads_running;
+extern bool printk_kthreads_ready;
 extern bool debug_non_panic_cpus;
 
 __printf(4, 0)
@@ -180,6 +181,7 @@ static inline void nbcon_kthread_wake(struct console *con)
 #define PRINTKRB_RECORD_MAX	0
 
 #define printk_kthreads_running (false)
+#define printk_kthreads_ready (false)
 
 /*
  * In !PRINTK builds we still export console_sem

kernel/printk/nbcon.c

@@ -1671,6 +1671,9 @@ bool nbcon_alloc(struct console *con)
 {
 	struct nbcon_state state = { };
 
+	/* Synchronize the kthread start. */
+	lockdep_assert_console_list_lock_held();
+
 	/* The write_thread() callback is mandatory. */
 	if (WARN_ON(!con->write_thread))
 		return false;
@@ -1701,12 +1704,15 @@ bool nbcon_alloc(struct console *con)
 			return false;
 		}
 
-		if (printk_kthreads_running) {
+		if (printk_kthreads_ready && !have_boot_console) {
 			if (!nbcon_kthread_create(con)) {
 				kfree(con->pbufs);
 				con->pbufs = NULL;
 				return false;
 			}
+
+			/* Might be the first kthread. */
+			printk_kthreads_running = true;
 		}
 	}
 
@@ -1716,14 +1722,30 @@ bool nbcon_alloc(struct console *con)
 /**
  * nbcon_free - Free and cleanup the nbcon console specific data
  * @con:	Console to free/cleanup nbcon data
+ *
+ * Important: @have_nbcon_console must be updated before calling
+ *	this function. In particular, it can be set only when there
+ *	is still another nbcon console registered.
  */
 void nbcon_free(struct console *con)
 {
 	struct nbcon_state state = { };
 
-	if (printk_kthreads_running)
+	/* Synchronize the kthread stop. */
+	lockdep_assert_console_list_lock_held();
+
+	if (printk_kthreads_running) {
 		nbcon_kthread_stop(con);
 
+		/* Might be the last nbcon console.
+		 *
+		 * Do not rely on printk_kthreads_check_locked(). It is not
+		 * called in some code paths, see nbcon_free() callers.
+		 */
+		if (!have_nbcon_console)
+			printk_kthreads_running = false;
+	}
+
 	nbcon_state_set(con, &state);
 
 	/* Boot consoles share global printk buffers. */

kernel/printk/printk.c

@@ -3574,7 +3574,7 @@ EXPORT_SYMBOL(console_resume);
 static int unregister_console_locked(struct console *console);
 
 /* True when system boot is far enough to create printer threads. */
-static bool printk_kthreads_ready __ro_after_init;
+bool printk_kthreads_ready __ro_after_init;
 
 static struct task_struct *printk_legacy_kthread;
 
@@ -3713,6 +3713,7 @@ static void printk_kthreads_check_locked(void)
 	if (!printk_kthreads_ready)
 		return;
 
+	/* Start or stop the legacy kthread when needed. */
 	if (have_legacy_console || have_boot_console) {
 		if (!printk_legacy_kthread &&
 		    force_legacy_kthread() &&
@@ -4204,14 +4205,6 @@ static int unregister_console_locked(struct console *console)
 	 */
 	synchronize_srcu(&console_srcu);
 
-	if (console->flags & CON_NBCON)
-		nbcon_free(console);
-
-	console_sysfs_notify();
-
-	if (console->exit)
-		res = console->exit(console);
-
 	/*
 	 * With this console gone, the global flags tracking registered
 	 * console types may have changed. Update them.
@@ -4232,6 +4225,15 @@ static int unregister_console_locked(struct console *console)
 	if (!found_nbcon_con)
 		have_nbcon_console = found_nbcon_con;
 
+	/* @have_nbcon_console must be updated before calling nbcon_free(). */
+	if (console->flags & CON_NBCON)
+		nbcon_free(console);
+
+	console_sysfs_notify();
+
+	if (console->exit)
+		res = console->exit(console);
+
 	/* Changed console list, may require printer threads to start/stop. */
 	printk_kthreads_check_locked();