linux-kernel - [PATCH printk v8 19/35] printk: nbcon: Add helper to assign priority based on CPU state

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Message-Id: <20240820063001.36405-20-john.ogness@linutronix.de>
Date: Tue, 20 Aug 2024 08:35:45 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Petr Mladek <pmladek@...e.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: [PATCH printk v8 19/35] printk: nbcon: Add helper to assign priority based on CPU state

Add a helper function to 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_device_try_acquire(), which is used by console
      drivers to acquire the nbcon console for non-printing
      activities, is hard-coded to always use NORMAL priority.

Signed-off-by: John Ogness <john.ogness@...utronix.de>
Reviewed-by: Petr Mladek <pmladek@...e.com>
---
 kernel/printk/internal.h |  2 ++
 kernel/printk/nbcon.c    | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index fe8d84d78f1c..72f229382cfa 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -83,6 +83,7 @@ u64 nbcon_seq_read(struct console *con);
 void nbcon_seq_force(struct console *con, u64 seq);
 bool nbcon_alloc(struct console *con);
 void nbcon_free(struct console *con);
+enum nbcon_prio nbcon_get_default_prio(void);
 
 /*
  * Check if the given console is currently capable and allowed to print
@@ -136,6 +137,7 @@ static inline u64 nbcon_seq_read(struct console *con) { return 0; }
 static inline void nbcon_seq_force(struct console *con, u64 seq) { }
 static inline bool nbcon_alloc(struct console *con) { return false; }
 static inline void nbcon_free(struct console *con) { }
+static inline enum nbcon_prio nbcon_get_default_prio(void) { return NBCON_PRIO_NONE; }
 
 static inline bool console_is_usable(struct console *con, short flags) { return false; }
 
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index e8ddcb6f7053..c6a9aa9f62f6 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -973,6 +973,25 @@ static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt)
 	return nbcon_context_exit_unsafe(ctxt);
 }
 
+/**
+ * nbcon_get_default_prio - The appropriate nbcon priority to use for nbcon
+ *				printing on the current CPU
+ *
+ * Context:	Any context.
+ * Return:	The nbcon_prio to use for acquiring an nbcon console in this
+ *		context for printing.
+ *
+ * The function is safe for reading per-CPU data in any context because
+ * preemption is disabled if the current CPU is in the panic state.
+ */
+enum nbcon_prio nbcon_get_default_prio(void)
+{
+	if (this_cpu_in_panic())
+		return NBCON_PRIO_PANIC;
+
+	return NBCON_PRIO_NORMAL;
+}
+
 /**
  * nbcon_alloc - Allocate and init the nbcon console specific data
  * @con:	Console to initialize
-- 
2.39.2