[mirror_ubuntu-artful-kernel.git] / drivers / oprofile / cpu_buffer.c

/**
 * @file cpu_buffer.c
 *
 * @remark Copyright 2002 OProfile authors
 * @remark Read the file COPYING
 *
 * @author John Levon <levon@movementarian.org>
 * @author Barry Kasindorf <barry.kasindorf@amd.com>
 *
 * Each CPU has a local buffer that stores PC value/event
 * pairs. We also log context switches when we notice them.
 * Eventually each CPU's buffer is processed into the global
 * event buffer by sync_buffer().
 *
 * We use a local buffer for two reasons: an NMI or similar
 * interrupt cannot synchronise, and high sampling rates
 * would lead to catastrophic global synchronisation if
 * a global buffer was used.
 */

#include <linux/sched.h>
#include <linux/oprofile.h>
#include <linux/vmalloc.h>
#include <linux/errno.h>

#include "event_buffer.h"
#include "cpu_buffer.h"
#include "buffer_sync.h"
#include "oprof.h"

DEFINE_PER_CPU(struct oprofile_cpu_buffer, cpu_buffer);

static void wq_sync_buffer(struct work_struct *work);

#define DEFAULT_TIMER_EXPIRE (HZ / 10)
static int work_enabled;

void free_cpu_buffers(void)
{
	int i;

	for_each_online_cpu(i) {
		vfree(per_cpu(cpu_buffer, i).buffer);
		per_cpu(cpu_buffer, i).buffer = NULL;
	}
}

int alloc_cpu_buffers(void)
{
	int i;

	unsigned long buffer_size = fs_cpu_buffer_size;

	for_each_online_cpu(i) {
		struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);

		b->buffer = vmalloc_node(sizeof(struct op_sample) * buffer_size,
			cpu_to_node(i));
		if (!b->buffer)
			goto fail;

		b->last_task = NULL;
		b->last_is_kernel = -1;
		b->tracing = 0;
		b->buffer_size = buffer_size;
		b->tail_pos = 0;
		b->head_pos = 0;
		b->sample_received = 0;
		b->sample_lost_overflow = 0;
		b->backtrace_aborted = 0;
		b->sample_invalid_eip = 0;
		b->cpu = i;
		INIT_DELAYED_WORK(&b->work, wq_sync_buffer);
	}
	return 0;

fail:
	free_cpu_buffers();
	return -ENOMEM;
}

void start_cpu_work(void)
{
	int i;

	work_enabled = 1;

	for_each_online_cpu(i) {
		struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);

		/*
		 * Spread the work by 1 jiffy per cpu so they dont all
		 * fire at once.
		 */
		schedule_delayed_work_on(i, &b->work, DEFAULT_TIMER_EXPIRE + i);
	}
}

void end_cpu_work(void)
{
	int i;

	work_enabled = 0;

	for_each_online_cpu(i) {
		struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);

		cancel_delayed_work(&b->work);
	}

	flush_scheduled_work();
}

/* Resets the cpu buffer to a sane state. */
void cpu_buffer_reset(struct oprofile_cpu_buffer *cpu_buf)
{
	/* reset these to invalid values; the next sample
	 * collected will populate the buffer with proper
	 * values to initialize the buffer
	 */
	cpu_buf->last_is_kernel = -1;
	cpu_buf->last_task = NULL;
}

/* compute number of available slots in cpu_buffer queue */
static unsigned long nr_available_slots(struct oprofile_cpu_buffer const *b)
{
	unsigned long head = b->head_pos;
	unsigned long tail = b->tail_pos;

	if (tail > head)
		return (tail - head) - 1;

	return tail + (b->buffer_size - head) - 1;
}

static void increment_head(struct oprofile_cpu_buffer *b)
{
	unsigned long new_head = b->head_pos + 1;

	/* Ensure anything written to the slot before we
	 * increment is visible */
	wmb();

	if (new_head < b->buffer_size)
		b->head_pos = new_head;
	else
		b->head_pos = 0;
}

static inline void
add_sample(struct oprofile_cpu_buffer *cpu_buf,
	   unsigned long pc, unsigned long event)
{
	struct op_sample *entry = &cpu_buf->buffer[cpu_buf->head_pos];
	entry->eip = pc;
	entry->event = event;
	increment_head(cpu_buf);
}

static inline void
add_code(struct oprofile_cpu_buffer *buffer, unsigned long value)
{
	add_sample(buffer, ESCAPE_CODE, value);
}

/* This must be safe from any context. It's safe writing here
 * because of the head/tail separation of the writer and reader
 * of the CPU buffer.
 *
 * is_kernel is needed because on some architectures you cannot
 * tell if you are in kernel or user space simply by looking at
 * pc. We tag this in the buffer by generating kernel enter/exit
 * events whenever is_kernel changes
 */
static int log_sample(struct oprofile_cpu_buffer *cpu_buf, unsigned long pc,
		      int is_kernel, unsigned long event)
{
	struct task_struct *task;

	cpu_buf->sample_received++;

	if (pc == ESCAPE_CODE) {
		cpu_buf->sample_invalid_eip++;
		return 0;
	}

	if (nr_available_slots(cpu_buf) < 3) {
		cpu_buf->sample_lost_overflow++;
		return 0;
	}

	is_kernel = !!is_kernel;

	task = current;

	/* notice a switch from user->kernel or vice versa */
	if (cpu_buf->last_is_kernel != is_kernel) {
		cpu_buf->last_is_kernel = is_kernel;
		add_code(cpu_buf, is_kernel);
	}

	/* notice a task switch */
	if (cpu_buf->last_task != task) {
		cpu_buf->last_task = task;
		add_code(cpu_buf, (unsigned long)task);
	}

	add_sample(cpu_buf, pc, event);
	return 1;
}

static int oprofile_begin_trace(struct oprofile_cpu_buffer *cpu_buf)
{
	if (nr_available_slots(cpu_buf) < 4) {
		cpu_buf->sample_lost_overflow++;
		return 0;
	}

	add_code(cpu_buf, CPU_TRACE_BEGIN);
	cpu_buf->tracing = 1;
	return 1;
}

static void oprofile_end_trace(struct oprofile_cpu_buffer *cpu_buf)
{
	cpu_buf->tracing = 0;
}

void oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
				unsigned long event, int is_kernel)
{
	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);

	if (!backtrace_depth) {
		log_sample(cpu_buf, pc, is_kernel, event);
		return;
	}

	if (!oprofile_begin_trace(cpu_buf))
		return;

	/* if log_sample() fail we can't backtrace since we lost the source
	 * of this event */
	if (log_sample(cpu_buf, pc, is_kernel, event))
		oprofile_ops.backtrace(regs, backtrace_depth);
	oprofile_end_trace(cpu_buf);
}

void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
{
	int is_kernel = !user_mode(regs);
	unsigned long pc = profile_pc(regs);

	oprofile_add_ext_sample(pc, regs, event, is_kernel);
}

#ifdef CONFIG_OPROFILE_IBS

#define MAX_IBS_SAMPLE_SIZE 14

void oprofile_add_ibs_sample(struct pt_regs *const regs,
			     unsigned int *const ibs_sample, int ibs_code)
{
	int is_kernel = !user_mode(regs);
	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
	struct task_struct *task;

	cpu_buf->sample_received++;

	if (nr_available_slots(cpu_buf) < MAX_IBS_SAMPLE_SIZE) {
		/* we can't backtrace since we lost the source of this event */
		cpu_buf->sample_lost_overflow++;
		return;
	}

	/* notice a switch from user->kernel or vice versa */
	if (cpu_buf->last_is_kernel != is_kernel) {
		cpu_buf->last_is_kernel = is_kernel;
		add_code(cpu_buf, is_kernel);
	}

	/* notice a task switch */
	if (!is_kernel) {
		task = current;
		if (cpu_buf->last_task != task) {
			cpu_buf->last_task = task;
			add_code(cpu_buf, (unsigned long)task);
		}
	}

	add_code(cpu_buf, ibs_code);
	add_sample(cpu_buf, ibs_sample[0], ibs_sample[1]);
	add_sample(cpu_buf, ibs_sample[2], ibs_sample[3]);
	add_sample(cpu_buf, ibs_sample[4], ibs_sample[5]);

	if (ibs_code == IBS_OP_BEGIN) {
		add_sample(cpu_buf, ibs_sample[6], ibs_sample[7]);
		add_sample(cpu_buf, ibs_sample[8], ibs_sample[9]);
		add_sample(cpu_buf, ibs_sample[10], ibs_sample[11]);
	}

	if (backtrace_depth)
		oprofile_ops.backtrace(regs, backtrace_depth);
}

#endif

void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event)
{
	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
	log_sample(cpu_buf, pc, is_kernel, event);
}

void oprofile_add_trace(unsigned long pc)
{
	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);

	if (!cpu_buf->tracing)
		return;

	if (nr_available_slots(cpu_buf) < 1) {
		cpu_buf->tracing = 0;
		cpu_buf->sample_lost_overflow++;
		return;
	}

	/* broken frame can give an eip with the same value as an escape code,
	 * abort the trace if we get it */
	if (pc == ESCAPE_CODE) {
		cpu_buf->tracing = 0;
		cpu_buf->backtrace_aborted++;
		return;
	}

	add_sample(cpu_buf, pc, 0);
}

/*
 * This serves to avoid cpu buffer overflow, and makes sure
 * the task mortuary progresses
 *
 * By using schedule_delayed_work_on and then schedule_delayed_work
 * we guarantee this will stay on the correct cpu
 */
static void wq_sync_buffer(struct work_struct *work)
{
	struct oprofile_cpu_buffer *b =
		container_of(work, struct oprofile_cpu_buffer, work.work);
	if (b->cpu != smp_processor_id()) {
		printk(KERN_DEBUG "WQ on CPU%d, prefer CPU%d\n",
		       smp_processor_id(), b->cpu);
	}
	sync_buffer(b->cpu);

	/* don't re-add the work if we're shutting down */
	if (work_enabled)
		schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE);
}
Commit	Line	Data
1da177e4 LT	1	/**
	2	* @file cpu_buffer.c
	3	*
	4	* @remark Copyright 2002 OProfile authors
	5	* @remark Read the file COPYING
	6	*
	7	* @author John Levon <levon@movementarian.org>
345c2573	8	* @author Barry Kasindorf <barry.kasindorf@amd.com>
1da177e4 LT	9	*
	10	* Each CPU has a local buffer that stores PC value/event
	11	* pairs. We also log context switches when we notice them.
	12	* Eventually each CPU's buffer is processed into the global
	13	* event buffer by sync_buffer().
	14	*
	15	* We use a local buffer for two reasons: an NMI or similar
	16	* interrupt cannot synchronise, and high sampling rates
	17	* would lead to catastrophic global synchronisation if
	18	* a global buffer was used.
	19	*/
	20
	21	#include <linux/sched.h>
	22	#include <linux/oprofile.h>
	23	#include <linux/vmalloc.h>
	24	#include <linux/errno.h>
6a18037d	25
1da177e4 LT	26	#include "event_buffer.h"
	27	#include "cpu_buffer.h"
	28	#include "buffer_sync.h"
	29	#include "oprof.h"
	30
8b8b4988	31	DEFINE_PER_CPU(struct oprofile_cpu_buffer, cpu_buffer);
1da177e4	32
c4028958	33	static void wq_sync_buffer(struct work_struct *work);
1da177e4 LT	34
	35	#define DEFAULT_TIMER_EXPIRE (HZ / 10)
	36	static int work_enabled;
	37
	38	void free_cpu_buffers(void)
	39	{
	40	int i;
6a18037d	41
f4156d1c	42	for_each_online_cpu(i) {
608dfddd	43	vfree(per_cpu(cpu_buffer, i).buffer);
f4156d1c CL	44	per_cpu(cpu_buffer, i).buffer = NULL;
f4156d1c CL	45	}
1da177e4	46	}
77933d72	47
1da177e4 LT	48	int alloc_cpu_buffers(void)
	49	{
	50	int i;
6a18037d	51
1da177e4	52	unsigned long buffer_size = fs_cpu_buffer_size;
6a18037d	53
1da177e4	54	for_each_online_cpu(i) {
608dfddd	55	struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
6a18037d	56
25ab7cd8 ED	57	b->buffer = vmalloc_node(sizeof(struct op_sample) * buffer_size,
25ab7cd8 ED	58	cpu_to_node(i));
1da177e4 LT	59	if (!b->buffer)
1da177e4 LT	60	goto fail;
6a18037d	61
1da177e4 LT	62	b->last_task = NULL;
	63	b->last_is_kernel = -1;
	64	b->tracing = 0;
	65	b->buffer_size = buffer_size;
	66	b->tail_pos = 0;
	67	b->head_pos = 0;
	68	b->sample_received = 0;
	69	b->sample_lost_overflow = 0;
df9d177a PE	70	b->backtrace_aborted = 0;
df9d177a PE	71	b->sample_invalid_eip = 0;
1da177e4	72	b->cpu = i;
c4028958	73	INIT_DELAYED_WORK(&b->work, wq_sync_buffer);
1da177e4 LT	74	}
	75	return 0;
	76
	77	fail:
	78	free_cpu_buffers();
	79	return -ENOMEM;
	80	}
1da177e4 LT	81
	82	void start_cpu_work(void)
	83	{
	84	int i;
	85
	86	work_enabled = 1;
	87
	88	for_each_online_cpu(i) {
608dfddd	89	struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
1da177e4 LT	90
	91	/*
	92	* Spread the work by 1 jiffy per cpu so they dont all
	93	* fire at once.
	94	*/
	95	schedule_delayed_work_on(i, &b->work, DEFAULT_TIMER_EXPIRE + i);
	96	}
	97	}
	98
1da177e4 LT	99	void end_cpu_work(void)
	100	{
	101	int i;
	102
	103	work_enabled = 0;
	104
	105	for_each_online_cpu(i) {
608dfddd	106	struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
1da177e4 LT	107
	108	cancel_delayed_work(&b->work);
	109	}
	110
	111	flush_scheduled_work();
	112	}
	113
1da177e4	114	/* Resets the cpu buffer to a sane state. */
25ad2913	115	void cpu_buffer_reset(struct oprofile_cpu_buffer *cpu_buf)
1da177e4 LT	116	{
	117	/* reset these to invalid values; the next sample
	118	* collected will populate the buffer with proper
	119	* values to initialize the buffer
	120	*/
	121	cpu_buf->last_is_kernel = -1;
	122	cpu_buf->last_task = NULL;
	123	}
	124
1da177e4	125	/* compute number of available slots in cpu_buffer queue */
25ad2913	126	static unsigned long nr_available_slots(struct oprofile_cpu_buffer const *b)
1da177e4 LT	127	{
	128	unsigned long head = b->head_pos;
	129	unsigned long tail = b->tail_pos;
	130
	131	if (tail > head)
	132	return (tail - head) - 1;
	133
	134	return tail + (b->buffer_size - head) - 1;
	135	}
	136
25ad2913	137	static void increment_head(struct oprofile_cpu_buffer *b)
1da177e4 LT	138	{
	139	unsigned long new_head = b->head_pos + 1;
	140
	141	/* Ensure anything written to the slot before we
	142	* increment is visible */
	143	wmb();
	144
	145	if (new_head < b->buffer_size)
	146	b->head_pos = new_head;
	147	else
	148	b->head_pos = 0;
	149	}
	150
77933d72	151	static inline void
25ad2913	152	add_sample(struct oprofile_cpu_buffer *cpu_buf,
6a18037d	153	unsigned long pc, unsigned long event)
1da177e4	154	{
25ad2913	155	struct op_sample *entry = &cpu_buf->buffer[cpu_buf->head_pos];
1da177e4 LT	156	entry->eip = pc;
	157	entry->event = event;
	158	increment_head(cpu_buf);
	159	}
	160
77933d72	161	static inline void
25ad2913	162	add_code(struct oprofile_cpu_buffer *buffer, unsigned long value)
1da177e4 LT	163	{
	164	add_sample(buffer, ESCAPE_CODE, value);
	165	}
	166
1da177e4 LT	167	/* This must be safe from any context. It's safe writing here
	168	* because of the head/tail separation of the writer and reader
	169	* of the CPU buffer.
	170	*
	171	* is_kernel is needed because on some architectures you cannot
	172	* tell if you are in kernel or user space simply by looking at
	173	* pc. We tag this in the buffer by generating kernel enter/exit
	174	* events whenever is_kernel changes
	175	*/
25ad2913	176	static int log_sample(struct oprofile_cpu_buffer *cpu_buf, unsigned long pc,
1da177e4 LT	177	int is_kernel, unsigned long event)
1da177e4 LT	178	{
25ad2913	179	struct task_struct *task;
1da177e4 LT	180
	181	cpu_buf->sample_received++;
	182
df9d177a PE	183	if (pc == ESCAPE_CODE) {
	184	cpu_buf->sample_invalid_eip++;
	185	return 0;
	186	}
	187
1da177e4 LT	188	if (nr_available_slots(cpu_buf) < 3) {
	189	cpu_buf->sample_lost_overflow++;
	190	return 0;
	191	}
	192
	193	is_kernel = !!is_kernel;
	194
	195	task = current;
	196
	197	/* notice a switch from user->kernel or vice versa */
	198	if (cpu_buf->last_is_kernel != is_kernel) {
	199	cpu_buf->last_is_kernel = is_kernel;
	200	add_code(cpu_buf, is_kernel);
	201	}
	202
	203	/* notice a task switch */
	204	if (cpu_buf->last_task != task) {
	205	cpu_buf->last_task = task;
	206	add_code(cpu_buf, (unsigned long)task);
	207	}
6a18037d	208
1da177e4 LT	209	add_sample(cpu_buf, pc, event);
	210	return 1;
	211	}
	212
345c2573	213	static int oprofile_begin_trace(struct oprofile_cpu_buffer *cpu_buf)
1da177e4 LT	214	{
	215	if (nr_available_slots(cpu_buf) < 4) {
	216	cpu_buf->sample_lost_overflow++;
	217	return 0;
	218	}
	219
	220	add_code(cpu_buf, CPU_TRACE_BEGIN);
	221	cpu_buf->tracing = 1;
	222	return 1;
	223	}
	224
25ad2913	225	static void oprofile_end_trace(struct oprofile_cpu_buffer *cpu_buf)
1da177e4 LT	226	{
	227	cpu_buf->tracing = 0;
	228	}
	229
27357716 BR	230	void oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
27357716 BR	231	unsigned long event, int is_kernel)
1da177e4	232	{
608dfddd	233	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
1da177e4 LT	234
	235	if (!backtrace_depth) {
	236	log_sample(cpu_buf, pc, is_kernel, event);
	237	return;
	238	}
	239
	240	if (!oprofile_begin_trace(cpu_buf))
	241	return;
	242
	243	/* if log_sample() fail we can't backtrace since we lost the source
	244	* of this event */
	245	if (log_sample(cpu_buf, pc, is_kernel, event))
	246	oprofile_ops.backtrace(regs, backtrace_depth);
	247	oprofile_end_trace(cpu_buf);
	248	}
	249
27357716 BR	250	void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
	251	{
	252	int is_kernel = !user_mode(regs);
	253	unsigned long pc = profile_pc(regs);
	254
	255	oprofile_add_ext_sample(pc, regs, event, is_kernel);
	256	}
	257
852402cc RR	258	#ifdef CONFIG_OPROFILE_IBS
852402cc RR	259
e2fee276 RR	260	#define MAX_IBS_SAMPLE_SIZE 14
	261
	262	void oprofile_add_ibs_sample(struct pt_regs *const regs,
25ad2913	263	unsigned int *const ibs_sample, int ibs_code)
345c2573	264	{
e2fee276 RR	265	int is_kernel = !user_mode(regs);
e2fee276 RR	266	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
345c2573 BK	267	struct task_struct *task;
	268
	269	cpu_buf->sample_received++;
	270
	271	if (nr_available_slots(cpu_buf) < MAX_IBS_SAMPLE_SIZE) {
e2fee276	272	/* we can't backtrace since we lost the source of this event */
345c2573	273	cpu_buf->sample_lost_overflow++;
e2fee276	274	return;
345c2573 BK	275	}
345c2573 BK	276
345c2573 BK	277	/* notice a switch from user->kernel or vice versa */
	278	if (cpu_buf->last_is_kernel != is_kernel) {
	279	cpu_buf->last_is_kernel = is_kernel;
	280	add_code(cpu_buf, is_kernel);
	281	}
	282
	283	/* notice a task switch */
	284	if (!is_kernel) {
	285	task = current;
345c2573 BK	286	if (cpu_buf->last_task != task) {
	287	cpu_buf->last_task = task;
	288	add_code(cpu_buf, (unsigned long)task);
	289	}
	290	}
	291
	292	add_code(cpu_buf, ibs_code);
e2fee276 RR	293	add_sample(cpu_buf, ibs_sample[0], ibs_sample[1]);
	294	add_sample(cpu_buf, ibs_sample[2], ibs_sample[3]);
	295	add_sample(cpu_buf, ibs_sample[4], ibs_sample[5]);
345c2573 BK	296
345c2573 BK	297	if (ibs_code == IBS_OP_BEGIN) {
e2fee276 RR	298	add_sample(cpu_buf, ibs_sample[6], ibs_sample[7]);
	299	add_sample(cpu_buf, ibs_sample[8], ibs_sample[9]);
	300	add_sample(cpu_buf, ibs_sample[10], ibs_sample[11]);
345c2573 BK	301	}
345c2573 BK	302
e2fee276	303	if (backtrace_depth)
345c2573 BK	304	oprofile_ops.backtrace(regs, backtrace_depth);
	305	}
	306
852402cc RR	307	#endif
852402cc RR	308
1da177e4 LT	309	void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event)
1da177e4 LT	310	{
608dfddd	311	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
1da177e4 LT	312	log_sample(cpu_buf, pc, is_kernel, event);
	313	}
	314
1da177e4 LT	315	void oprofile_add_trace(unsigned long pc)
1da177e4 LT	316	{
608dfddd	317	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
1da177e4 LT	318
	319	if (!cpu_buf->tracing)
	320	return;
	321
	322	if (nr_available_slots(cpu_buf) < 1) {
	323	cpu_buf->tracing = 0;
	324	cpu_buf->sample_lost_overflow++;
	325	return;
	326	}
	327
	328	/* broken frame can give an eip with the same value as an escape code,
	329	* abort the trace if we get it */
	330	if (pc == ESCAPE_CODE) {
	331	cpu_buf->tracing = 0;
	332	cpu_buf->backtrace_aborted++;
	333	return;
	334	}
	335
	336	add_sample(cpu_buf, pc, 0);
	337	}
	338
1da177e4 LT	339	/*
	340	* This serves to avoid cpu buffer overflow, and makes sure
	341	* the task mortuary progresses
	342	*
	343	* By using schedule_delayed_work_on and then schedule_delayed_work
	344	* we guarantee this will stay on the correct cpu
	345	*/
c4028958	346	static void wq_sync_buffer(struct work_struct *work)
1da177e4	347	{
25ad2913	348	struct oprofile_cpu_buffer *b =
c4028958	349	container_of(work, struct oprofile_cpu_buffer, work.work);
1da177e4	350	if (b->cpu != smp_processor_id()) {
bd17b625	351	printk(KERN_DEBUG "WQ on CPU%d, prefer CPU%d\n",
1da177e4 LT	352	smp_processor_id(), b->cpu);
	353	}
	354	sync_buffer(b->cpu);
	355
	356	/* don't re-add the work if we're shutting down */
	357	if (work_enabled)
	358	schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE);
	359	}