linux-kernel - [RFC][PATCHv3 4/5] printk: enable printk offloading

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Date:   Tue,  9 May 2017 17:28:58 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Jan Kara <jack@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Eric Biederman <ebiederm@...ssion.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, Pavel Machek <pavel@....cz>,
        Andreas Mohr <andi@...as.de>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: [RFC][PATCHv3 4/5] printk: enable printk offloading

Initialize kernel printing thread and make printk offloading
possible. By default `atomic_print_limit' is set to 0, so no
offloading will take place, unless requested by user.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
---
 kernel/printk/printk.c | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ba640fbcee7c..81ea575728b9 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -49,6 +49,7 @@
 #include <linux/sched/debug.h>
 #include <linux/sched/task_stack.h>
 #include <linux/kthread.h>
+#include <uapi/linux/sched/types.h>
 
 #include <linux/uaccess.h>
 #include <asm/sections.h>
@@ -2927,6 +2928,43 @@ static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) = {
 	.flags = IRQ_WORK_LAZY,
 };
 
+static int printk_kthread_func(void *data)
+{
+	while (1) {
+		set_current_state(TASK_INTERRUPTIBLE);
+		if (!test_bit(PRINTK_PENDING_OUTPUT, &printk_pending))
+			schedule();
+
+		__set_current_state(TASK_RUNNING);
+
+		console_lock();
+		console_unlock();
+	}
+
+	return 0;
+}
+
+/*
+ * Init printk kthread at late_initcall stage, after core/arch/device/etc.
+ * initialization.
+ */
+static int __init init_printk_kthread(void)
+{
+	struct task_struct *thread;
+	struct sched_param param = { .sched_priority = MAX_USER_RT_PRIO / 2 };
+
+	thread = kthread_run(printk_kthread_func, NULL, "printk");
+	if (IS_ERR(thread)) {
+		pr_err("printk: unable to create printing thread\n");
+		return PTR_ERR(thread);
+	}
+
+	sched_setscheduler(thread, SCHED_FIFO, &param);
+	printk_kthread = thread;
+	return 0;
+}
+late_initcall(init_printk_kthread);
+
 void wake_up_klogd(void)
 {
 	preempt_disable();
-- 
2.12.2