linux-kernel - [PATCH printk v2 17/26] printk: nbcon: Assign priority based on CPU state

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Date: Sun, 18 Feb 2024 20:03:17 +0106
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 v2 17/26] 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.

Note: The uart_port wrapper, which is responsible for non-console-
      printing activities, will always use NORMAL priority.

Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
 kernel/printk/internal.h |  2 ++
 kernel/printk/nbcon.c    | 30 ++++++++++++++++++++++++++++--
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index b34847ec6b0d..70e9a1ea75be 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -79,6 +79,7 @@ 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_all(void);
 bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
 				   int cookie);
@@ -136,6 +137,7 @@ 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_all(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 747f5cbfe5ee..1a18549e43b8 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -961,6 +961,22 @@ 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
@@ -994,7 +1010,7 @@ 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);
 
@@ -1038,7 +1054,6 @@ static void __nbcon_atomic_flush_all(u64 stop_seq)
 			memset(ctxt, 0, sizeof(*ctxt));
 			ctxt->console			= con;
 			ctxt->spinwait_max_us		= 2000;
-			ctxt->prio			= NBCON_PRIO_NORMAL;
 
 			/*
 			 * Atomic flushing does not use console driver
@@ -1047,9 +1062,14 @@ static void __nbcon_atomic_flush_all(u64 stop_seq)
 			 * disabled to avoid being interrupted and then
 			 * calling into a driver that will deadlock trying
 			 * acquire console ownership.
+			 *
+			 * This also disables migration in order to get the
+			 * current CPU priority.
 			 */
 			local_irq_save(irq_flags);
 
+			ctxt->prio = nbcon_get_default_prio();
+
 			any_progress |= nbcon_atomic_emit_one(&wctxt);
 
 			local_irq_restore(irq_flags);
@@ -1161,6 +1181,9 @@ static inline bool uart_is_nbcon(struct uart_port *up)
  *
  * If @up is an nbcon console, this console will be acquired and marked as
  * unsafe. Otherwise this function does nothing.
+ *
+ * nbcon consoles acquired via the port lock wrapper always use priority
+ * NBCON_PRIO_NORMAL.
  */
 void uart_nbcon_acquire(struct uart_port *up)
 {
@@ -1195,6 +1218,9 @@ EXPORT_SYMBOL_GPL(uart_nbcon_acquire);
  *
  * If @up is an nbcon console, the console will be marked as safe and
  * released. Otherwise this function does nothing.
+ *
+ * nbcon consoles acquired via the port lock wrapper always use priority
+ * NBCON_PRIO_NORMAL.
  */
 void uart_nbcon_release(struct uart_port *up)
 {
-- 
2.39.2