printk: Perform atomic flush in console_flush_on_panic()

Typically the panic() function will take care of atomic flushing the
non-BKL consoles on panic. However, there are several users of
console_flush_on_panic() outside of panic().

Also perform atomic flushing in console_flush_on_panic(). A new
function cons_force_seq() is implemented to support the
mode=CONSOLE_REPLAY_ALL feature.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

kernel/printk/internal.h

@@ -79,6 +79,7 @@ bool cons_nobkl_init(struct console *con);
 bool cons_alloc_percpu_data(struct console *con);
 void cons_kthread_create(struct console *con);
 void cons_wake_threads(void);
+void cons_force_seq(struct console *con, u64 seq);
 
 /*
  * Check if the given console is currently capable and allowed to print
@@ -149,6 +150,7 @@ static inline bool printk_percpu_data_ready(void) { return false; }
 static inline bool cons_nobkl_init(struct console *con) { return true; }
 static inline void cons_nobkl_cleanup(struct console *con) { }
 static inline bool console_is_usable(struct console *con, short flags) { return false; }
+static inline void cons_force_seq(struct console *con, u64 seq) { }
 
 #endif /* CONFIG_PRINTK */
 

kernel/printk/printk.c

@@ -3166,8 +3166,29 @@ void console_unblank(void)
  */
 void console_flush_on_panic(enum con_flush_mode mode)
 {
+	struct console *c;
 	bool handover;
 	u64 next_seq;
+	short flags;
+	int cookie;
+	u64 seq;
+
+	seq = prb_first_valid_seq(prb);
+
+	/*
+	 * Safely flush the atomic consoles before trying to flush any
+	 * BKL/legacy consoles.
+	 */
+	if (mode == CONSOLE_REPLAY_ALL) {
+		cookie = console_srcu_read_lock();
+		for_each_console_srcu(c) {
+			flags = console_srcu_read_flags(c);
+			if (flags & CON_NO_BKL)
+				cons_force_seq(c, seq);
+		}
+		console_srcu_read_unlock(cookie);
+	}
+	cons_atomic_flush(NULL, true);
 
 	if (!have_bkl_console)
 		return;
@@ -3190,12 +3211,6 @@ void console_flush_on_panic(enum con_flush_mode mode)
 	console_may_schedule = 0;
 
 	if (mode == CONSOLE_REPLAY_ALL) {
-		struct console *c;
-		int cookie;
-		u64 seq;
-
-		seq = prb_first_valid_seq(prb);
-
 		cookie = console_srcu_read_lock();
 		for_each_console_srcu(c) {
 			/*

kernel/printk/printk_nobkl.c

@@ -233,6 +233,30 @@ static void cons_seq_init(struct console *con)
 #endif
 }
 
+/**
+ * cons_force_seq - Force a specified sequence number for a console
+ * @con:	Console to work on
+ * @seq:	Sequence number to force
+ *
+ * This function is only intended to be used in emergency situations. In
+ * particular: console_flush_on_panic(CONSOLE_REPLAY_ALL)
+ */
+void cons_force_seq(struct console *con, u64 seq)
+{
+#ifdef CONFIG_64BIT
+	struct cons_state old;
+	struct cons_state new;
+
+	do {
+		cons_state_read(con, CON_STATE_CUR, &old);
+		copy_bit_state(new, old);
+		new.seq = seq;
+	} while (!cons_state_try_cmpxchg(con, CON_STATE_CUR, &old, &new));
+#else
+	atomic_set(&ACCESS_PRIVATE(con, atomic_seq), seq);
+#endif
+}
+
 static inline u64 cons_expand_seq(u64 seq)
 {
 	u64 rbseq;