printk: Introduce FORCE_CON flag

Introduce FORCE_CON flag to printk. The new flag will make it possible to
create a context where printk messages will never be suppressed.

This mechanism will be used in the next patch to create a force_con
context on sysrq handling, removing an existing workaround on the
loglevel global variable. The workaround existed to make sure that sysrq
header messages were sent to all consoles, but this doesn't work with
deferred messages because the loglevel might be restored to its original
value before a console flushes the messages.

Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20241105-printk-loud-con-v2-1-bd3ecdf7b0e4@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index 2b35a9d3919d..6f94418d53ff 100644
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -12,6 +12,24 @@
 
 #include "internal.h"
 
+/* Context where printk messages are never suppressed */
+static atomic_t force_con;
+
+void printk_force_console_enter(void)
+{
+	atomic_inc(&force_con);
+}
+
+void printk_force_console_exit(void)
+{
+	atomic_dec(&force_con);
+}
+
+bool is_printk_force_console(void)
+{
+	return atomic_read(&force_con);
+}
+
 static DEFINE_PER_CPU(int, printk_context);
 
 /* Can be preempted by NMI. */