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Commit b845b517 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

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: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 796aadeb

include/linux/kernel.h

+4 −0
Original line number Diff line number Diff line
@@ -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)))

kernel/printk.c

+17 −2
Original line number Diff line number Diff line
@@ -982,11 +982,26 @@ 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;

}



/**

 * release_console_sem - unlock the console system

kernel/time/tick-sched.c

+1 −1
Original line number Diff line number Diff line
@@ -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

kernel/timer.c

+1 −0
Original line number Diff line number Diff line
@@ -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);

}