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Commit 3ccf3e83 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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printk/sched: Introduce special printk_sched() for those awkward moments 



There's a few awkward printk()s inside of scheduler guts that people
prefer to keep but really are rather deadlock prone. Fudge around it
by storing the text in a per-cpu buffer and poll it using the existing
printk_tick() handler.

This will drop output when its more frequent than once a tick, however
only the affinity thing could possible go that fast and for that just
one should suffice to notify the admin he's done something silly..

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-wua3lmkt3dg8nfts66o6brne@git.kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 554cecaf

include/linux/printk.h

+10 −0
Original line number Diff line number Diff line
@@ -100,6 +100,11 @@ int vprintk(const char *fmt, va_list args); 
asmlinkage __printf(1, 2) __cold

int printk(const char *fmt, ...);



/*

 * Special printk facility for scheduler use only, _DO_NOT_USE_ !

 */

__printf(1, 2) __cold int printk_sched(const char *fmt, ...);



/*

 * Please don't use printk_ratelimit(), because it shares ratelimiting state

 * with all other unrelated printk_ratelimit() callsites.  Instead use
@@ -127,6 +132,11 @@ int printk(const char *s, ...) 
{

	return 0;

}

static inline __printf(1, 2) __cold

int printk_sched(const char *s, ...)

{

	return 0;

}

static inline int printk_ratelimit(void)

{

	return 0;

kernel/printk.c

+37 −3
Original line number Diff line number Diff line
@@ -1208,12 +1208,46 @@ int is_console_locked(void) 
	return console_locked;

}



/*

 * Delayed printk facility, for scheduler-internal messages:

 */

#define PRINTK_BUF_SIZE		512



#define PRINTK_PENDING_WAKEUP	0x01

#define PRINTK_PENDING_SCHED	0x02



static DEFINE_PER_CPU(int, printk_pending);

static DEFINE_PER_CPU(char [PRINTK_BUF_SIZE], printk_sched_buf);



int printk_sched(const char *fmt, ...)

{

	unsigned long flags;

	va_list args;

	char *buf;

	int r;



	local_irq_save(flags);

	buf = __get_cpu_var(printk_sched_buf);



	va_start(args, fmt);

	r = vsnprintf(buf, PRINTK_BUF_SIZE, fmt, args);

	va_end(args);



	__this_cpu_or(printk_pending, PRINTK_PENDING_SCHED);

	local_irq_restore(flags);



	return r;

}



void printk_tick(void)

{

	if (__this_cpu_read(printk_pending)) {

		__this_cpu_write(printk_pending, 0);

		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);

	}

}
@@ -1228,7 +1262,7 @@ int printk_needs_cpu(int cpu) 
void wake_up_klogd(void)

{

	if (waitqueue_active(&log_wait))

		this_cpu_write(printk_pending, 1);

		this_cpu_or(printk_pending, PRINTK_PENDING_WAKEUP);

}



/**

kernel/sched/core.c

+1 −1
Original line number Diff line number Diff line
@@ -1284,7 +1284,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p) 
	 * leave kernel.

	 */

	if (p->mm && printk_ratelimit()) {

		printk(KERN_INFO "process %d (%s) no longer affine to cpu%d\n",

		printk_sched("process %d (%s) no longer affine to cpu%d\n",

				task_pid_nr(p), p->comm, cpu);

	}

kernel/sched/rt.c

+7 −1
Original line number Diff line number Diff line
@@ -864,8 +864,14 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq) 
		 * but accrue some time due to boosting.

		 */

		if (likely(rt_b->rt_runtime)) {

			static bool once = false;



			rt_rq->rt_throttled = 1;

			printk_once(KERN_WARNING "sched: RT throttling activated\n");



			if (!once) {

				once = true;

				printk_sched("sched: RT throttling activated\n");

			}

		} else {

			/*

			 * In case we did anyway, make it go away,