[tip: sched/rt] printk: nbcon: Flush new records on device_release()

[tip-bot2 for John Ogness]

The following commit has been merged into the sched/rt branch of tip:

Commit-ID:     8ba77712a7501ca941603d6d5ed650cd0d42cafb
Gitweb:        https://git.kernel.org/tip/8ba77712a7501ca941603d6d5ed650cd0d42cafb
Author:        John Ogness <john.ogness@xxxxxxxxxxxxx>
AuthorDate:    Tue, 20 Aug 2024 08:35:50 +02:06
Committer:     Petr Mladek <pmladek@xxxxxxxx>
CommitterDate: Wed, 21 Aug 2024 14:56:24 +02:00

printk: nbcon: Flush new records on device_release()

There may be new records that were added while a driver was
holding the nbcon context for non-printing purposes. These
new records must be flushed by the nbcon_device_release()
context because no other context will do it.

If boot consoles are registered, the legacy loop is used
(either direct or per irq_work) to handle the flushing.

Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
Link: https://lore.kernel.org/r/20240820063001.36405-25-john.ogness@xxxxxxxxxxxxx
Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
---
 kernel/printk/internal.h |  2 ++
 kernel/printk/nbcon.c    | 20 ++++++++++++++++++++
 kernel/printk/printk.c   |  2 +-
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 84706c1..7679e18 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -153,6 +153,8 @@ static inline bool console_is_usable(struct console *con, short flags) { return 
 
 #endif /* CONFIG_PRINTK */
 
+extern bool have_boot_console;
+
 extern struct printk_buffers printk_shared_pbufs;
 
 /**
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index d09c084..269aeed 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -1326,10 +1326,30 @@ EXPORT_SYMBOL_GPL(nbcon_device_try_acquire);
 void nbcon_device_release(struct console *con)
 {
 	struct nbcon_context *ctxt = &ACCESS_PRIVATE(con, nbcon_device_ctxt);
+	int cookie;
 
 	if (!nbcon_context_exit_unsafe(ctxt))
 		return;
 
 	nbcon_context_release(ctxt);
+
+	/*
+	 * This context must flush any new records added while the console
+	 * was locked. The console_srcu_read_lock must be taken to ensure
+	 * the console is usable throughout flushing.
+	 */
+	cookie = console_srcu_read_lock();
+	if (console_is_usable(con, console_srcu_read_flags(con)) &&
+	    prb_read_valid(prb, nbcon_seq_read(con), NULL)) {
+		if (!have_boot_console) {
+			__nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb));
+		} else if (!is_printk_legacy_deferred()) {
+			if (console_trylock())
+				console_unlock();
+		} else {
+			printk_trigger_flush();
+		}
+	}
+	console_srcu_read_unlock(cookie);
 }
 EXPORT_SYMBOL_GPL(nbcon_device_release);
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index f08bf5e..7c9f8f6 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -469,7 +469,7 @@ static DEFINE_MUTEX(syslog_lock);
  * the console lock. This is because boot consoles and nbcon consoles may
  * have mapped the same hardware.
  */
-static bool have_boot_console;
+bool have_boot_console;
 
 #ifdef CONFIG_PRINTK
 DECLARE_WAIT_QUEUE_HEAD(log_wait);