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From: John Ogness <john.ogness@linutronix.de>
Date: Thu, 14 Dec 2023 14:38:42 +0000
Subject: [PATCH 111/134] printk: nbcon: Assign priority based on CPU state
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz
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@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/printk/internal.h | 2 ++
kernel/printk/nbcon.c | 30 ++++++++++++++++++++++++++++--
2 files changed, 30 insertions(+), 2 deletions(-)
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -79,6 +79,7 @@ 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_all(void);
bool nbcon_atomic_emit_next_record(struct console *con, bool *handover, int cookie);
@@ -135,6 +136,7 @@ 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_all(void) { }
static inline bool nbcon_atomic_emit_next_record(struct console *con, bool *handover,
int cookie) { return false; }
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -962,6 +962,22 @@ 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_atomic_emit_next_record - Print one record for an nbcon console
* using the write_atomic() callback
* @con: The console to print on
@@ -997,7 +1013,7 @@ bool nbcon_atomic_emit_next_record(struc
cant_migrate();
ctxt->console = con;
- ctxt->prio = NBCON_PRIO_NORMAL;
+ ctxt->prio = nbcon_get_default_prio();
progress = nbcon_atomic_emit_one(&wctxt);
@@ -1043,7 +1059,6 @@ static void __nbcon_atomic_flush_all(u64
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
@@ -1052,9 +1067,14 @@ static void __nbcon_atomic_flush_all(u64
* 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);
@@ -1166,6 +1186,9 @@ static inline bool uart_is_nbcon(struct
*
* 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 nbcon_acquire(struct uart_port *up)
{
@@ -1200,6 +1223,9 @@ EXPORT_SYMBOL_GPL(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 nbcon_release(struct uart_port *up)
{
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