Subject: [PATCH 23/48] printk: nbcon: Assign priority based on CPU state
From: John Ogness <[email-masked]>
Date: Thu, 14 Dec 2023 14:38:42 +0000

Use the current state of the CPU to determine which priority to
assign to the printing context.

The EMERGENCY priority handling is added in a follow-up commit.
It will use a per-CPU variable.

Note: nbcon_driver_acquire(), which is used by console drivers
      to acquire the nbcon console for non-printing activities,
      will always use NORMAL priority.

Signed-off-by: John Ogness <[email-masked]>
Reviewed-by: Petr Mladek <[email-masked]>
Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 kernel/printk/internal.h |    2 ++
 kernel/printk/nbcon.c    |   20 ++++++++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

Index: linux-6.8.2-rt10/kernel/printk/internal.h
===================================================================
--- linux-6.8.2-rt10.orig/kernel/printk/internal.h
+++ linux-6.8.2-rt10/kernel/printk/internal.h
@@ -86,6 +86,7 @@ void nbcon_seq_force(struct console *con
 bool nbcon_alloc(struct console *con);
 void nbcon_init(struct console *con);
 void nbcon_free(struct console *con);
+enum nbcon_prio nbcon_get_default_prio(void);
 void nbcon_atomic_flush_pending(void);
 bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
 				   int cookie);
@@ -143,6 +144,7 @@ static inline void nbcon_seq_force(struc
 static inline bool nbcon_alloc(struct console *con) { return false; }
 static inline void nbcon_init(struct console *con) { }
 static inline void nbcon_free(struct console *con) { }
+static inline enum nbcon_prio nbcon_get_default_prio(void) { return NBCON_PRIO_NONE; }
 static inline void nbcon_atomic_flush_pending(void) { }
 static inline bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
 						 int cookie) { return false; }
Index: linux-6.8.2-rt10/kernel/printk/nbcon.c
===================================================================
--- linux-6.8.2-rt10.orig/kernel/printk/nbcon.c
+++ linux-6.8.2-rt10/kernel/printk/nbcon.c
@@ -968,6 +968,22 @@ static bool nbcon_atomic_emit_one(struct
 }
 
 /**
+ * nbcon_get_default_prio - The appropriate nbcon priority to use for nbcon
+ *				printing on the current CPU
+ *
+ * Context:	Any context which could not be migrated to another CPU.
+ * Return:	The nbcon_prio to use for acquiring an nbcon console in this
+ *		context for printing.
+ */
+enum nbcon_prio nbcon_get_default_prio(void)
+{
+	if (this_cpu_in_panic())
+		return NBCON_PRIO_PANIC;
+
+	return NBCON_PRIO_NORMAL;
+}
+
+/**
  * nbcon_legacy_emit_next_record - Print one record for an nbcon console
  *					in legacy contexts
  * @con:	The console to print on
@@ -1001,7 +1017,7 @@ bool nbcon_legacy_emit_next_record(struc
 	stop_critical_timings();
 
 	ctxt->console	= con;
-	ctxt->prio	= NBCON_PRIO_NORMAL;
+	ctxt->prio	= nbcon_get_default_prio();
 
 	progress = nbcon_atomic_emit_one(&wctxt);
 
@@ -1032,7 +1048,7 @@ static bool __nbcon_atomic_flush_pending
 
 	ctxt->console			= con;
 	ctxt->spinwait_max_us		= 2000;
-	ctxt->prio			= NBCON_PRIO_NORMAL;
+	ctxt->prio			= nbcon_get_default_prio();
 
 	if (!nbcon_context_try_acquire(ctxt))
 		return false;