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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>
This commit is contained in:
Peter Zijlstra 2008-08-08 21:47:09 +02:00 committed by Ingo Molnar
parent 796aadeb1b
commit b845b517b5
4 changed files with 23 additions and 3 deletions
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4
include/linux/kernel.h
View File

@ -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)))

19
kernel/printk.c
View File

@ -982,10 +982,25 @@ int is_console_locked(void)
return console_locked;
}
static DEFINE_PER_CPU(int, printk_pending);
void printk_tick(void)
{
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 (!oops_in_progress && waitqueue_active(&log_wait))
wake_up_interruptible(&log_wait);
if (waitqueue_active(&log_wait))
__get_cpu_var(printk_pending) = 1;
}
/**

2
kernel/time/tick-sched.c
View File

@ -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

1
kernel/timer.c
View File

@ -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);
}