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: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Steven 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>

diff --git a/include/linux/printk.h b/include/linux/printk.h
index 9afc01e5a0a61ce5f4a9fe1e53ad6e0fb1b8e5bf..86c4b6294713a613fff6d8c3150691967baa6124 100644 (file)
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -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,

diff --git a/init/Kconfig b/init/Kconfig
index cdc152c75727409683864f26816912423db4563c..c575566be47d46801ac3af27c8ecf30494644696 100644 (file)
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -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

diff --git a/kernel/printk.c b/kernel/printk.c
index 2d607f4d1797cb02e0e4fb60453312a8d3491975..c9104feba5ece1b0a6edea7309ed0cdb6b7ab5ff 100644 (file)
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -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 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);
        }
-}
 
-int printk_needs_cpu(int cpu)
-{
-       if (cpu_is_offline(cpu))
-               printk_tick();
-       return __this_cpu_read(printk_pending);
+       if (pending & PRINTK_PENDING_WAKEUP)
+               wake_up_interruptible(&log_wait);
 }
 
+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;

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index f249e8c3e58e47410c3fee619f59c94aca4dc2bd..822d7572bf2dcb35163ff6e8aacc5bd440fd6d2b 100644 (file)
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -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;

diff --git a/kernel/timer.c b/kernel/timer.c
index 367d008584823a6fe01ed013cda8c3693fcfd761..ff3b5165737bab3e8c87914f07ed8997ce99db3d 100644 (file)
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -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();