Commit 74876a98 authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

printk: Wake up klogd using irq_work 



klogd is woken up asynchronously from the tick in order
to do it safely.

However if printk is called when the tick is stopped, the reader
won't be woken up until the next interrupt, which might not fire
for a while. As a result, the user may miss some message.

To fix this, lets implement the printk tick using a lazy irq work.
This subsystem takes care of the timer tick state and can
fix up accordingly.

Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
parent bc6679ae

include/linux/printk.h

+0 −3
Original line number Diff line number Diff line
@@ -98,9 +98,6 @@ int no_printk(const char *fmt, ...) 
extern asmlinkage __printf(1, 2)

void early_printk(const char *fmt, ...);



extern int printk_needs_cpu(int cpu);

extern void printk_tick(void);



#ifdef CONFIG_PRINTK

asmlinkage __printf(5, 0)

int vprintk_emit(int facility, int level,

init/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -1196,6 +1196,7 @@ config HOTPLUG 
config PRINTK

	default y

	bool "Enable support for printk" if EXPERT

	select IRQ_WORK

	help

	  This option enables normal printk support. Removing it

	  eliminates most of the message strings from the kernel image

kernel/printk.c

+20 −16
Original line number Diff line number Diff line
@@ -42,6 +42,7 @@ 
#include <linux/notifier.h>

#include <linux/rculist.h>

#include <linux/poll.h>

#include <linux/irq_work.h>



#include <asm/uaccess.h>
@@ -1955,30 +1956,32 @@ int is_console_locked(void) 
static DEFINE_PER_CPU(int, printk_pending);

static DEFINE_PER_CPU(char [PRINTK_BUF_SIZE], printk_sched_buf);



void printk_tick(void)

static void wake_up_klogd_work_func(struct irq_work *irq_work)

{

	if (__this_cpu_read(printk_pending)) {

	int pending = __this_cpu_xchg(printk_pending, 0);



	if (pending & PRINTK_PENDING_SCHED) {

		char *buf = __get_cpu_var(printk_sched_buf);

		printk(KERN_WARNING "[sched_delayed] %s", buf);

	}



	if (pending & PRINTK_PENDING_WAKEUP)

		wake_up_interruptible(&log_wait);

}

}



int printk_needs_cpu(int cpu)

{

	if (cpu_is_offline(cpu))

		printk_tick();

	return __this_cpu_read(printk_pending);

}

static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) = {

	.func = wake_up_klogd_work_func,

	.flags = IRQ_WORK_LAZY,

};



void wake_up_klogd(void)

{

	if (waitqueue_active(&log_wait))

	preempt_disable();

	if (waitqueue_active(&log_wait)) {

		this_cpu_or(printk_pending, PRINTK_PENDING_WAKEUP);

		irq_work_queue(&__get_cpu_var(wake_up_klogd_work));

	}

	preempt_enable();

}



static void console_cont_flush(char *text, size_t size)
@@ -2458,6 +2461,7 @@ int printk_sched(const char *fmt, ...) 
	va_end(args);



	__this_cpu_or(printk_pending, PRINTK_PENDING_SCHED);

	irq_work_queue(&__get_cpu_var(wake_up_klogd_work));

	local_irq_restore(flags);



	return r;

kernel/time/tick-sched.c

+1 −1
Original line number Diff line number Diff line
@@ -289,7 +289,7 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, 
		time_delta = timekeeping_max_deferment();

	} while (read_seqretry(&xtime_lock, seq));



	if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) || printk_needs_cpu(cpu) ||

	if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) ||

	    arch_needs_cpu(cpu) || irq_work_needs_cpu()) {

		next_jiffies = last_jiffies + 1;

		delta_jiffies = 1;

kernel/timer.c

+0 −1
Original line number Diff line number Diff line
@@ -1351,7 +1351,6 @@ void update_process_times(int user_tick) 
	account_process_tick(p, user_tick);

	run_local_timers();

	rcu_check_callbacks(cpu, user_tick);

	printk_tick();

#ifdef CONFIG_IRQ_WORK

	if (in_irq())

		irq_work_run();