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-rw-r--r--debian/patches-rt/0021-printk-Track-registered-boot-consoles.patch79
1 files changed, 79 insertions, 0 deletions
diff --git a/debian/patches-rt/0021-printk-Track-registered-boot-consoles.patch b/debian/patches-rt/0021-printk-Track-registered-boot-consoles.patch
new file mode 100644
index 0000000000..64ee0c4dbb
--- /dev/null
+++ b/debian/patches-rt/0021-printk-Track-registered-boot-consoles.patch
@@ -0,0 +1,79 @@
+From: John Ogness <john.ogness@linutronix.de>
+Date: Tue, 24 Oct 2023 14:13:14 +0000
+Subject: [PATCH 21/48] printk: Track registered boot consoles
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.8/older/patches-6.8.2-rt11.tar.xz
+
+Unfortunately it is not known if a boot console and a regular
+(legacy or nbcon) console use the same hardware. For this reason
+they must not be allowed to print simultaneously.
+
+For legacy consoles this is not an issue because they are
+already synchronized with the boot consoles using the console
+lock. However nbcon consoles can be triggered separately.
+
+Add a global flag @have_boot_console to identify if any boot
+consoles are registered. This will be used in follow-up commits
+to ensure that boot consoles and nbcon consoles cannot print
+simultaneously.
+
+Signed-off-by: John Ogness <john.ogness@linutronix.de>
+Reviewed-by: Petr Mladek <pmladek@suse.com>
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ kernel/printk/printk.c | 24 ++++++++++++++++++++++++
+ 1 file changed, 24 insertions(+)
+
+--- a/kernel/printk/printk.c
++++ b/kernel/printk/printk.c
+@@ -463,6 +463,14 @@ static int console_msg_format = MSG_FORM
+ /* syslog_lock protects syslog_* variables and write access to clear_seq. */
+ static DEFINE_MUTEX(syslog_lock);
+
++/*
++ * Specifies if a boot console is registered. If boot consoles are present,
++ * nbcon consoles cannot print simultaneously and must be synchronized by
++ * the console lock. This is because boot consoles and nbcon consoles may
++ * have mapped the same hardware.
++ */
++static bool have_boot_console;
++
+ #ifdef CONFIG_PRINTK
+ DECLARE_WAIT_QUEUE_HEAD(log_wait);
+ /* All 3 protected by @syslog_lock. */
+@@ -3518,6 +3526,9 @@ void register_console(struct console *ne
+ newcon->seq = 0;
+ }
+
++ if (newcon->flags & CON_BOOT)
++ have_boot_console = true;
++
+ /*
+ * If another context is actively using the hardware of this new
+ * console, it will not be aware of the nbcon synchronization. This
+@@ -3587,6 +3598,8 @@ EXPORT_SYMBOL(register_console);
+ /* Must be called under console_list_lock(). */
+ static int unregister_console_locked(struct console *console)
+ {
++ bool found_boot_con = false;
++ struct console *c;
+ int res;
+
+ lockdep_assert_console_list_lock_held();
+@@ -3634,6 +3647,17 @@ static int unregister_console_locked(str
+ if (console->exit)
+ res = console->exit(console);
+
++ /*
++ * With this console gone, the global flags tracking registered
++ * console types may have changed. Update them.
++ */
++ for_each_console(c) {
++ if (c->flags & CON_BOOT)
++ found_boot_con = true;
++ }
++ if (!found_boot_con)
++ have_boot_console = found_boot_con;
++
+ return res;
+ }
+