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Message-Id: <20230302195618.156940-13-john.ogness@linutronix.de>
Date: Thu, 2 Mar 2023 21:02:12 +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,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH printk v1 12/18] printk: nobkl: Add printer thread wakeups
From: Thomas Gleixner <tglx@...utronix.de>
Add a function to wakeup the printer threads. Use the new function
when:
- records are added to the printk ringbuffer
- consoles are started
- consoles are resumed
The actual waking is performed via irq_work so that the wakeup can
be triggered from any context.
Co-developed-by: John Ogness <john.ogness@...utronix.de>
Signed-off-by: John Ogness <john.ogness@...utronix.de>
Signed-off-by: Thomas Gleixner (Intel) <tglx@...utronix.de>
---
include/linux/console.h | 3 +++
kernel/printk/internal.h | 1 +
kernel/printk/printk.c | 26 ++++++++++++++++++++++++++
kernel/printk/printk_nobkl.c | 32 ++++++++++++++++++++++++++++++++
4 files changed, 62 insertions(+)
diff --git a/include/linux/console.h b/include/linux/console.h
index 2c120c3f3c6e..710f1e72cd0f 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -16,6 +16,7 @@
#include <linux/atomic.h>
#include <linux/bits.h>
+#include <linux/irq_work.h>
#include <linux/rculist.h>
#include <linux/rcuwait.h>
#include <linux/types.h>
@@ -317,6 +318,7 @@ struct cons_context_data;
* @thread_pbufs: Pointer to thread private buffer
* @kthread: Pointer to kernel thread
* @rcuwait: RCU wait for the kernel thread
+ * @irq_work: IRQ work for thread wakeup
* @kthread_waiting: Indicator whether the kthread is waiting to be woken
* @write_atomic: Write callback for atomic context
* @write_thread: Write callback for printk threaded printing
@@ -350,6 +352,7 @@ struct console {
struct printk_buffers *thread_pbufs;
struct task_struct *kthread;
struct rcuwait rcuwait;
+ struct irq_work irq_work;
atomic_t kthread_waiting;
bool (*write_atomic)(struct console *con, struct cons_write_context *wctxt);
diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 8856beed65da..a72402c1ac93 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -78,6 +78,7 @@ void cons_nobkl_cleanup(struct console *con);
bool cons_nobkl_init(struct console *con);
bool cons_alloc_percpu_data(struct console *con);
void cons_kthread_create(struct console *con);
+void cons_wake_threads(void);
/*
* Check if the given console is currently capable and allowed to print
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 4c6abb033ec1..19f682fcae10 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2345,6 +2345,7 @@ asmlinkage int vprintk_emit(int facility, int level,
preempt_enable();
}
+ cons_wake_threads();
if (in_sched)
defer_console_output();
else
@@ -2615,6 +2616,8 @@ void suspend_console(void)
void resume_console(void)
{
struct console *con;
+ short flags;
+ int cookie;
if (!console_suspend_enabled)
return;
@@ -2634,6 +2637,14 @@ void resume_console(void)
*/
synchronize_srcu(&console_srcu);
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(con) {
+ flags = console_srcu_read_flags(con);
+ if (flags & CON_NO_BKL)
+ cons_kthread_wake(con);
+ }
+ console_srcu_read_unlock(cookie);
+
pr_flush(1000, true);
}
@@ -3226,9 +3237,23 @@ EXPORT_SYMBOL(console_stop);
void console_start(struct console *console)
{
+ short flags;
+
console_list_lock();
console_srcu_write_flags(console, console->flags | CON_ENABLED);
+ flags = console->flags;
console_list_unlock();
+
+ /*
+ * Ensure that all SRCU list walks have completed. The related
+ * printing context must be able to see it is enabled so that
+ * it is guaranteed to wake up and resume printing.
+ */
+ synchronize_srcu(&console_srcu);
+
+ if (flags & CON_NO_BKL)
+ cons_kthread_wake(console);
+
__pr_flush(console, 1000, true);
}
EXPORT_SYMBOL(console_start);
@@ -3918,6 +3943,7 @@ void defer_console_output(void)
void printk_trigger_flush(void)
{
+ cons_wake_threads();
defer_console_output();
}
diff --git a/kernel/printk/printk_nobkl.c b/kernel/printk/printk_nobkl.c
index bc3b69223897..890fc8d44f1d 100644
--- a/kernel/printk/printk_nobkl.c
+++ b/kernel/printk/printk_nobkl.c
@@ -1368,6 +1368,37 @@ static int cons_kthread_func(void *__console)
return 0;
}
+/**
+ * cons_irq_work - irq work to wake printk thread
+ * @irq_work: The irq work to operate on
+ */
+static void cons_irq_work(struct irq_work *irq_work)
+{
+ struct console *con = container_of(irq_work, struct console, irq_work);
+
+ cons_kthread_wake(con);
+}
+
+/**
+ * cons_wake_threads - Wake up printing threads
+ *
+ * A printing thread is only woken if it is within the @kthread_waiting
+ * block. If it is not within the block (or enters the block later), it
+ * will see any new records and continue printing on its own.
+ */
+void cons_wake_threads(void)
+{
+ struct console *con;
+ int cookie;
+
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(con) {
+ if (con->kthread && atomic_read(&con->kthread_waiting))
+ irq_work_queue(&con->irq_work);
+ }
+ console_srcu_read_unlock(cookie);
+}
+
/**
* cons_kthread_stop - Stop a printk thread
* @con: Console to operate on
@@ -1471,6 +1502,7 @@ bool cons_nobkl_init(struct console *con)
rcuwait_init(&con->rcuwait);
atomic_set(&con->kthread_waiting, 0);
+ init_irq_work(&con->irq_work, cons_irq_work);
cons_state_set(con, CON_STATE_CUR, &state);
cons_state_set(con, CON_STATE_REQ, &state);
cons_seq_init(con);
--
2.30.2
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