[PATCH] printk: Clean up code initializing the per-console sequence number

[Petr Mladek]

console_init_seq() reads either con->seq or con->nbcon_seq
depending on the value of CON_NBCON flag. But it always sets
newcon->seq even for nbcon consoles. The value is later
moved in register_console().

Rename console_init_seq() to get_init_console_seq() and just
return the value. Pass the value to nbcon_init() so that
it might be initialized there.

The cleaned design should make sure that the value stays
and is set before the kthread is created.

Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
---
 kernel/printk/internal.h |  2 +-
 kernel/printk/nbcon.c    |  5 +++--
 kernel/printk/printk.c   | 37 +++++++++++++++++--------------------
 3 files changed, 21 insertions(+), 23 deletions(-)

diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index bcf2105a5c5c..2366303f31ae 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -84,7 +84,7 @@ int console_lock_spinning_disable_and_check(int cookie);
 u64 nbcon_seq_read(struct console *con);
 void nbcon_seq_force(struct console *con, u64 seq);
 bool nbcon_alloc(struct console *con);
-void nbcon_init(struct console *con);
+void nbcon_init(struct console *con, u64 init_seq);
 void nbcon_free(struct console *con);
 enum nbcon_prio nbcon_get_default_prio(void);
 void nbcon_atomic_flush_pending(void);
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index 4c852c2e8d89..c57ad34a8d56 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -1262,18 +1262,19 @@ bool nbcon_alloc(struct console *con)
 /**
  * nbcon_init - Initialize the nbcon console specific data
  * @con:	Console to initialize
+ * @init_seq	Sequence number of the first to-be-emitted record
  *
  * nbcon_alloc() *must* be called and succeed before this function
  * is called.
  */
-void nbcon_init(struct console *con)
+void nbcon_init(struct console *con, u64 init_seq)
 {
 	struct nbcon_state state = { };
 
 	/* nbcon_alloc() must have been called and successful! */
 	BUG_ON(!con->pbufs);
 
-	nbcon_seq_force(con, 0);
+	nbcon_seq_force(con, init_seq);
 	nbcon_state_set(con, &state);
 }
 
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 9da70d7dda3d..9164b7f72e17 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3427,20 +3427,21 @@ static void try_enable_default_console(struct console *newcon)
 		newcon->flags |= CON_CONSDEV;
 }
 
-/* Set @newcon->seq to the first record this console should print. */
-static void console_init_seq(struct console *newcon, bool bootcon_registered)
+/* Return starting sequence number to be used by a newly registered console. */
+static u64 get_init_console_seq(struct console *newcon, bool bootcon_registered)
 {
 	struct console *con;
+	u64 init_seq;
 	bool handover;
 
 	if (newcon->flags & (CON_PRINTBUFFER | CON_BOOT)) {
 		/* Get a consistent copy of @syslog_seq. */
 		mutex_lock(&syslog_lock);
-		newcon->seq = syslog_seq;
+		init_seq = syslog_seq;
 		mutex_unlock(&syslog_lock);
 	} else {
 		/* Begin with next message added to ringbuffer. */
-		newcon->seq = prb_next_seq(prb);
+		init_seq = prb_next_seq(prb);
 
 		/*
 		 * If any enabled boot consoles are due to be unregistered
@@ -3461,7 +3462,7 @@ static void console_init_seq(struct console *newcon, bool bootcon_registered)
 			 * Flush all consoles and set the console to start at
 			 * the next unprinted sequence number.
 			 */
-			if (!console_flush_all(true, &newcon->seq, &handover)) {
+			if (!console_flush_all(true, &init_seq, &handover)) {
 				/*
 				 * Flushing failed. Just choose the lowest
 				 * sequence of the enabled boot consoles.
@@ -3474,12 +3475,12 @@ static void console_init_seq(struct console *newcon, bool bootcon_registered)
 				if (handover)
 					console_lock();
 
-				newcon->seq = prb_next_seq(prb);
+				init_seq = prb_next_seq(prb);
 				for_each_console(con) {
 					u64 seq;
 
-					if (!((con->flags & CON_BOOT) &&
-					      (con->flags & CON_ENABLED))) {
+					if (!(con->flags & CON_BOOT) ||
+					    !(con->flags & CON_ENABLED)) {
 						continue;
 					}
 
@@ -3488,14 +3489,16 @@ static void console_init_seq(struct console *newcon, bool bootcon_registered)
 					else
 						seq = con->seq;
 
-					if (seq < newcon->seq)
-						newcon->seq = seq;
+					if (seq < init_seq)
+						init_seq = seq;
 				}
 			}
 
 			console_unlock();
 		}
 	}
+
+	return init_seq;
 }
 
 #define console_first()				\
@@ -3528,6 +3531,7 @@ void register_console(struct console *newcon)
 	bool bootcon_registered = false;
 	bool realcon_registered = false;
 	unsigned long flags;
+	u64 init_seq;
 	int err;
 
 	console_list_lock();
@@ -3605,21 +3609,14 @@ void register_console(struct console *newcon)
 	}
 
 	newcon->dropped = 0;
-	console_init_seq(newcon, bootcon_registered);
+	init_seq = get_init_console_seq(newcon, have_boot_console);
 
 	if (newcon->flags & CON_NBCON) {
 		have_nbcon_console = true;
-		nbcon_init(newcon);
-
-		/*
-		 * nbcon consoles have their own sequence counter. The legacy
-		 * sequence counter is reset so that it is clear it is not
-		 * being used.
-		 */
-		nbcon_seq_force(newcon, newcon->seq);
-		newcon->seq = 0;
+		nbcon_init(newcon, init_seq);
 	} else {
 		have_legacy_console = true;
+		newcon->seq = init_seq;
 	}
 
 	if (newcon->flags & CON_BOOT)
-- 
2.44.0