[tip: sched/rt] printk: nbcon: Add helper to assign priority based on CPU state

[tip-bot2 for John Ogness]

The following commit has been merged into the sched/rt branch of tip:

Commit-ID:     06683a6649895ccf279c35ca2fb77fd7afb7a6c5
Gitweb:        https://git.kernel.org/tip/06683a6649895ccf279c35ca2fb77fd7afb7a6c5
Author:        John Ogness <john.ogness@xxxxxxxxxxxxx>
AuthorDate:    Tue, 20 Aug 2024 08:35:45 +02:06
Committer:     Petr Mladek <pmladek@xxxxxxxx>
CommitterDate: Wed, 21 Aug 2024 14:56:24 +02:00

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@xxxxxxxxxxxxx>
Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
Link: https://lore.kernel.org/r/20240820063001.36405-20-john.ogness@xxxxxxxxxxxxx
Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
---
 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 fe8d84d..72f2293 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 e8ddcb6..c6a9aa9 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -974,6 +974,25 @@ update_con:
 }
 
 /**
+ * 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
  *