From b845b517b5e3706a3729f6ea83b88ab85f0725b0 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Fri, 8 Aug 2008 21:47:09 +0200
Subject: [PATCH] printk: robustify printk
Avoid deadlocks against rq->lock and xtime_lock by deferring the klogd
wakeup by polling from the timer tick.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
include/linux/kernel.h | 4 ++++
kernel/printk.c | 19 +++++++++++++++++--
kernel/time/tick-sched.c | 2 +-
kernel/timer.c | 1 +
4 files changed, 23 insertions(+), 3 deletions(-)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index aaa998f..113ac8d 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -200,6 +200,8 @@ extern struct ratelimit_state printk_ratelimit_state;
extern int printk_ratelimit(void);
extern bool printk_timed_ratelimit(unsigned long *caller_jiffies,
unsigned int interval_msec);
+extern void printk_tick(void);
+extern int printk_needs_cpu(int);
#else
static inline int vprintk(const char *s, va_list args)
__attribute__ ((format (printf, 1, 0)));
@@ -211,6 +213,8 @@ static inline int printk_ratelimit(void) { return 0; }
static inline bool printk_timed_ratelimit(unsigned long *caller_jiffies, \
unsigned int interval_msec) \
{ return false; }
+static inline void printk_tick(void) { }
+static inline int printk_needs_cpu(int) { return 0; }
#endif
extern void asmlinkage __attribute__((format(printf, 1, 2)))
diff --git a/kernel/printk.c b/kernel/printk.c
index b51b156..655cc2c 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -982,10 +982,25 @@ int is_console_locked(void)
return console_locked;
}
-void wake_up_klogd(void)
+static DEFINE_PER_CPU(int, printk_pending);
+
+void printk_tick(void)
{
- if (!oops_in_progress && waitqueue_active(&log_wait))
+ if (__get_cpu_var(printk_pending)) {
+ __get_cpu_var(printk_pending) = 0;
wake_up_interruptible(&log_wait);
+ }
+}
+
+int printk_needs_cpu(int cpu)
+{
+ return per_cpu(printk_pending, cpu);
+}
+
+void wake_up_klogd(void)
+{
+ if (waitqueue_active(&log_wait))
+ __get_cpu_var(printk_pending) = 1;
}
/**
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 825b4c0..c13d4f1 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -255,7 +255,7 @@ void tick_nohz_stop_sched_tick(int inidle)
next_jiffies = get_next_timer_interrupt(last_jiffies);
delta_jiffies = next_jiffies - last_jiffies;
- if (rcu_needs_cpu(cpu))
+ if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu))
delta_jiffies = 1;
/*
* Do not stop the tick, if we are only one off
diff --git a/kernel/timer.c b/kernel/timer.c
index 03bc7f1..510fe69 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -978,6 +978,7 @@ void update_process_times(int user_tick)
run_local_timers();
if (rcu_pending(cpu))
rcu_check_callbacks(cpu, user_tick);
+ printk_tick();
scheduler_tick();
run_posix_cpu_timers(p);
}
--
1.9.1