[RFC][PATCHv6 05/12] printk: enable printk offloading

Sergey Senozhatsky
2017-12-04T13:49:22Z

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

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
kernel/printk/printk.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 59 insertions(+)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 16f5f5c7e541..a427cee2aa00 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2914,6 +2914,65 @@ 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);
+ /*
+ * We must check `printk_emergency' as well, to let
+ * printk_emergency_begin() stop active `printk_kthread' at
+ * some point. Otherwise we can end up in a loop:
+ * - we bail out of console_unlock() because of
+ * printk_kthread_should_stop()
+ * and
+ * - don't schedule() and attempt to return back
+ * immediately to console_unlock() because we
+ * see PRINTK_PENDING_OUTPUT bit set.
+ */
+ if (!test_bit(PRINTK_PENDING_OUTPUT, &printk_pending) ||
+ atomic_read(&printk_emergency) != 0)
+ schedule();
+
+ __set_current_state(TASK_RUNNING);
+
+ /* We might have been woken for stop */
+ if (kthread_should_park())
+ kthread_parkme();
+
+ console_lock();
+ console_unlock();
+
+ /* We might have been blocked on console_sem */
+ if (kthread_should_park())
+ kthread_parkme();
+ }
+
+ 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;
+
+ if (!alloc_cpumask_var(&printk_offload_cpus, GFP_KERNEL))
+ return -ENOMEM;
+
+ thread = kthread_run(printk_kthread_func, NULL, "printk");
+ if (IS_ERR(thread)) {
+ pr_err("printk: unable to create printing thread\n");
+ free_cpumask_var(printk_offload_cpus);
+ return PTR_ERR(thread);
+ }
+
+ printk_kthread = thread;
+ return 0;
+}
+late_initcall(init_printk_kthread);
+
void wake_up_klogd(void)
{
preempt_disable();
--
2.15.1