linux-kernel - [PATCH printk v4 18/27] printk: nbcon: Assign priority based on CPU state

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Date: Wed,  3 Apr 2024 00:17:20 +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 v4 18/27] printk: nbcon: Assign priority based on CPU state

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 <john.ogness@...utronix.de>
Reviewed-by: Petr Mladek <pmladek@...e.com>
---
 kernel/printk/internal.h |  2 ++
 kernel/printk/nbcon.c    | 20 ++++++++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index acf53c35b7a0..bcf2105a5c5c 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -86,6 +86,7 @@ void nbcon_seq_force(struct console *con, u64 seq);
 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(struct console *con, u64 seq) { }
 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; }
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index 599fff3c0ab3..fe5a96ab1f40 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -967,6 +967,22 @@ static bool nbcon_atomic_emit_one(struct nbcon_write_context *wctxt)
 	return ctxt->backlog;
 }
 
+/**
+ * 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
@@ -1001,7 +1017,7 @@ bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
 	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_con(struct console *con, u64 stop_seq)
 
 	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;
-- 
2.39.2