[RFC][PATCHv3 4/5] printk: enable printk offloading

Sergey Senozhatsky
2017-05-09T08:30:28Z

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@gmail.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