[thirdparty/linux.git] / kernel / printk / printk_safe.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * printk_safe.c - Safe printk for printk-deadlock-prone contexts
 */

#include <linux/preempt.h>
#include <linux/spinlock.h>
#include <linux/debug_locks.h>
#include <linux/smp.h>
#include <linux/cpumask.h>
#include <linux/irq_work.h>
#include <linux/printk.h>

#include "internal.h"

/*
 * printk() could not take logbuf_lock in NMI context. Instead,
 * it uses an alternative implementation that temporary stores
 * the strings into a per-CPU buffer. The content of the buffer
 * is later flushed into the main ring buffer via IRQ work.
 *
 * The alternative implementation is chosen transparently
 * by examinig current printk() context mask stored in @printk_context
 * per-CPU variable.
 *
 * The implementation allows to flush the strings also from another CPU.
 * There are situations when we want to make sure that all buffers
 * were handled or when IRQs are blocked.
 */

#define SAFE_LOG_BUF_LEN ((1 << CONFIG_PRINTK_SAFE_LOG_BUF_SHIFT) -	\
				sizeof(atomic_t) -			\
				sizeof(atomic_t) -			\
				sizeof(struct irq_work))

struct printk_safe_seq_buf {
	atomic_t		len;	/* length of written data */
	atomic_t		message_lost;
	struct irq_work		work;	/* IRQ work that flushes the buffer */
	unsigned char		buffer[SAFE_LOG_BUF_LEN];
};

static DEFINE_PER_CPU(struct printk_safe_seq_buf, safe_print_seq);
static DEFINE_PER_CPU(int, printk_context);

#ifdef CONFIG_PRINTK_NMI
static DEFINE_PER_CPU(struct printk_safe_seq_buf, nmi_print_seq);
#endif

/* Get flushed in a more safe context. */
static void queue_flush_work(struct printk_safe_seq_buf *s)
{
	if (printk_percpu_data_ready())
		irq_work_queue(&s->work);
}

/*
 * Add a message to per-CPU context-dependent buffer. NMI and printk-safe
 * have dedicated buffers, because otherwise printk-safe preempted by
 * NMI-printk would have overwritten the NMI messages.
 *
 * The messages are flushed from irq work (or from panic()), possibly,
 * from other CPU, concurrently with printk_safe_log_store(). Should this
 * happen, printk_safe_log_store() will notice the buffer->len mismatch
 * and repeat the write.
 */
static __printf(2, 0) int printk_safe_log_store(struct printk_safe_seq_buf *s,
						const char *fmt, va_list args)
{
	int add;
	size_t len;
	va_list ap;

again:
	len = atomic_read(&s->len);

	/* The trailing '\0' is not counted into len. */
	if (len >= sizeof(s->buffer) - 1) {
		atomic_inc(&s->message_lost);
		queue_flush_work(s);
		return 0;
	}

	/*
	 * Make sure that all old data have been read before the buffer
	 * was reset. This is not needed when we just append data.
	 */
	if (!len)
		smp_rmb();

	va_copy(ap, args);
	add = vscnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, ap);
	va_end(ap);
	if (!add)
		return 0;

	/*
	 * Do it once again if the buffer has been flushed in the meantime.
	 * Note that atomic_cmpxchg() is an implicit memory barrier that
	 * makes sure that the data were written before updating s->len.
	 */
	if (atomic_cmpxchg(&s->len, len, len + add) != len)
		goto again;

	queue_flush_work(s);
	return add;
}

static inline void printk_safe_flush_line(const char *text, int len)
{
	/*
	 * Avoid any console drivers calls from here, because we may be
	 * in NMI or printk_safe context (when in panic). The messages
	 * must go only into the ring buffer at this stage.  Consoles will
	 * get explicitly called later when a crashdump is not generated.
	 */
	printk_deferred("%.*s", len, text);
}

/* printk part of the temporary buffer line by line */
static int printk_safe_flush_buffer(const char *start, size_t len)
{
	const char *c, *end;
	bool header;

	c = start;
	end = start + len;
	header = true;

	/* Print line by line. */
	while (c < end) {
		if (*c == '\n') {
			printk_safe_flush_line(start, c - start + 1);
			start = ++c;
			header = true;
			continue;
		}

		/* Handle continuous lines or missing new line. */
		if ((c + 1 < end) && printk_get_level(c)) {
			if (header) {
				c = printk_skip_level(c);
				continue;
			}

			printk_safe_flush_line(start, c - start);
			start = c++;
			header = true;
			continue;
		}

		header = false;
		c++;
	}

	/* Check if there was a partial line. Ignore pure header. */
	if (start < end && !header) {
		static const char newline[] = KERN_CONT "\n";

		printk_safe_flush_line(start, end - start);
		printk_safe_flush_line(newline, strlen(newline));
	}

	return len;
}

static void report_message_lost(struct printk_safe_seq_buf *s)
{
	int lost = atomic_xchg(&s->message_lost, 0);

	if (lost)
		printk_deferred("Lost %d message(s)!\n", lost);
}

/*
 * Flush data from the associated per-CPU buffer. The function
 * can be called either via IRQ work or independently.
 */
static void __printk_safe_flush(struct irq_work *work)
{
	static raw_spinlock_t read_lock =
		__RAW_SPIN_LOCK_INITIALIZER(read_lock);
	struct printk_safe_seq_buf *s =
		container_of(work, struct printk_safe_seq_buf, work);
	unsigned long flags;
	size_t len;
	int i;

	/*
	 * The lock has two functions. First, one reader has to flush all
	 * available message to make the lockless synchronization with
	 * writers easier. Second, we do not want to mix messages from
	 * different CPUs. This is especially important when printing
	 * a backtrace.
	 */
	raw_spin_lock_irqsave(&read_lock, flags);

	i = 0;
more:
	len = atomic_read(&s->len);

	/*
	 * This is just a paranoid check that nobody has manipulated
	 * the buffer an unexpected way. If we printed something then
	 * @len must only increase. Also it should never overflow the
	 * buffer size.
	 */
	if ((i && i >= len) || len > sizeof(s->buffer)) {
		const char *msg = "printk_safe_flush: internal error\n";

		printk_safe_flush_line(msg, strlen(msg));
		len = 0;
	}

	if (!len)
		goto out; /* Someone else has already flushed the buffer. */

	/* Make sure that data has been written up to the @len */
	smp_rmb();
	i += printk_safe_flush_buffer(s->buffer + i, len - i);

	/*
	 * Check that nothing has got added in the meantime and truncate
	 * the buffer. Note that atomic_cmpxchg() is an implicit memory
	 * barrier that makes sure that the data were copied before
	 * updating s->len.
	 */
	if (atomic_cmpxchg(&s->len, len, 0) != len)
		goto more;

out:
	report_message_lost(s);
	raw_spin_unlock_irqrestore(&read_lock, flags);
}

/**
 * printk_safe_flush - flush all per-cpu nmi buffers.
 *
 * The buffers are flushed automatically via IRQ work. This function
 * is useful only when someone wants to be sure that all buffers have
 * been flushed at some point.
 */
void printk_safe_flush(void)
{
	int cpu;

	for_each_possible_cpu(cpu) {
#ifdef CONFIG_PRINTK_NMI
		__printk_safe_flush(&per_cpu(nmi_print_seq, cpu).work);
#endif
		__printk_safe_flush(&per_cpu(safe_print_seq, cpu).work);
	}
}

/**
 * printk_safe_flush_on_panic - flush all per-cpu nmi buffers when the system
 *	goes down.
 *
 * Similar to printk_safe_flush() but it can be called even in NMI context when
 * the system goes down. It does the best effort to get NMI messages into
 * the main ring buffer.
 *
 * Note that it could try harder when there is only one CPU online.
 */
void printk_safe_flush_on_panic(void)
{
	/*
	 * Make sure that we could access the main ring buffer.
	 * Do not risk a double release when more CPUs are up.
	 */
	if (raw_spin_is_locked(&logbuf_lock)) {
		if (num_online_cpus() > 1)
			return;

		debug_locks_off();
		raw_spin_lock_init(&logbuf_lock);
	}

	printk_safe_flush();
}

#ifdef CONFIG_PRINTK_NMI
/*
 * Safe printk() for NMI context. It uses a per-CPU buffer to
 * store the message. NMIs are not nested, so there is always only
 * one writer running. But the buffer might get flushed from another
 * CPU, so we need to be careful.
 */
static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
{
	struct printk_safe_seq_buf *s = this_cpu_ptr(&nmi_print_seq);

	return printk_safe_log_store(s, fmt, args);
}

void notrace printk_nmi_enter(void)
{
	this_cpu_or(printk_context, PRINTK_NMI_CONTEXT_MASK);
}

void notrace printk_nmi_exit(void)
{
	this_cpu_and(printk_context, ~PRINTK_NMI_CONTEXT_MASK);
}

/*
 * Marks a code that might produce many messages in NMI context
 * and the risk of losing them is more critical than eventual
 * reordering.
 *
 * It has effect only when called in NMI context. Then printk()
 * will try to store the messages into the main logbuf directly
 * and use the per-CPU buffers only as a fallback when the lock
 * is not available.
 */
void printk_nmi_direct_enter(void)
{
	if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
		this_cpu_or(printk_context, PRINTK_NMI_DIRECT_CONTEXT_MASK);
}

void printk_nmi_direct_exit(void)
{
	this_cpu_and(printk_context, ~PRINTK_NMI_DIRECT_CONTEXT_MASK);
}

#else

static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
{
	return 0;
}

#endif /* CONFIG_PRINTK_NMI */

/*
 * Lock-less printk(), to avoid deadlocks should the printk() recurse
 * into itself. It uses a per-CPU buffer to store the message, just like
 * NMI.
 */
static __printf(1, 0) int vprintk_safe(const char *fmt, va_list args)
{
	struct printk_safe_seq_buf *s = this_cpu_ptr(&safe_print_seq);

	return printk_safe_log_store(s, fmt, args);
}

/* Can be preempted by NMI. */
void __printk_safe_enter(void)
{
	this_cpu_inc(printk_context);
}

/* Can be preempted by NMI. */
void __printk_safe_exit(void)
{
	this_cpu_dec(printk_context);
}

__printf(1, 0) int vprintk_func(const char *fmt, va_list args)
{
	/*
	 * Try to use the main logbuf even in NMI. But avoid calling console
	 * drivers that might have their own locks.
	 */
	if ((this_cpu_read(printk_context) & PRINTK_NMI_DIRECT_CONTEXT_MASK) &&
	    raw_spin_trylock(&logbuf_lock)) {
		int len;

		len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
		raw_spin_unlock(&logbuf_lock);
		defer_console_output();
		return len;
	}

	/* Use extra buffer in NMI when logbuf_lock is taken or in safe mode. */
	if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
		return vprintk_nmi(fmt, args);

	/* Use extra buffer to prevent a recursion deadlock in safe mode. */
	if (this_cpu_read(printk_context) & PRINTK_SAFE_CONTEXT_MASK)
		return vprintk_safe(fmt, args);

	/* No obstacles. */
	return vprintk_default(fmt, args);
}

void __init printk_safe_init(void)
{
	int cpu;

	for_each_possible_cpu(cpu) {
		struct printk_safe_seq_buf *s;

		s = &per_cpu(safe_print_seq, cpu);
		init_irq_work(&s->work, __printk_safe_flush);

#ifdef CONFIG_PRINTK_NMI
		s = &per_cpu(nmi_print_seq, cpu);
		init_irq_work(&s->work, __printk_safe_flush);
#endif
	}

	/* Flush pending messages that did not have scheduled IRQ works. */
	printk_safe_flush();
}
Commit	Line	Data
1ccea77e	1	// SPDX-License-Identifier: GPL-2.0-or-later
42a0bb3f	2	/*
099f1c84	3	* printk_safe.c - Safe printk for printk-deadlock-prone contexts
42a0bb3f PM	4	*/
	5
	6	#include <linux/preempt.h>
	7	#include <linux/spinlock.h>
cf9b1106	8	#include <linux/debug_locks.h>
42a0bb3f PM	9	#include <linux/smp.h>
	10	#include <linux/cpumask.h>
	11	#include <linux/irq_work.h>
	12	#include <linux/printk.h>
	13
	14	#include "internal.h"
	15
	16	/*
	17	* printk() could not take logbuf_lock in NMI context. Instead,
	18	* it uses an alternative implementation that temporary stores
	19	* the strings into a per-CPU buffer. The content of the buffer
	20	* is later flushed into the main ring buffer via IRQ work.
	21	*
	22	* The alternative implementation is chosen transparently
099f1c84 SS	23	* by examinig current printk() context mask stored in @printk_context
099f1c84 SS	24	* per-CPU variable.
42a0bb3f PM	25	*
	26	* The implementation allows to flush the strings also from another CPU.
	27	* There are situations when we want to make sure that all buffers
	28	* were handled or when IRQs are blocked.
	29	*/
42a0bb3f	30
f92bac3b	31	#define SAFE_LOG_BUF_LEN ((1 << CONFIG_PRINTK_SAFE_LOG_BUF_SHIFT) - \
ddb9baa8 SS	32	sizeof(atomic_t) - \
	33	sizeof(atomic_t) - \
	34	sizeof(struct irq_work))
42a0bb3f	35
f92bac3b	36	struct printk_safe_seq_buf {
42a0bb3f	37	atomic_t len; /* length of written data */
ddb9baa8	38	atomic_t message_lost;
42a0bb3f	39	struct irq_work work; /* IRQ work that flushes the buffer */
f92bac3b	40	unsigned char buffer[SAFE_LOG_BUF_LEN];
42a0bb3f	41	};
099f1c84 SS	42
	43	static DEFINE_PER_CPU(struct printk_safe_seq_buf, safe_print_seq);
	44	static DEFINE_PER_CPU(int, printk_context);
	45
	46	#ifdef CONFIG_PRINTK_NMI
f92bac3b	47	static DEFINE_PER_CPU(struct printk_safe_seq_buf, nmi_print_seq);
099f1c84	48	#endif
42a0bb3f	49
ddb9baa8 SS	50	/* Get flushed in a more safe context. */
	51	static void queue_flush_work(struct printk_safe_seq_buf *s)
	52	{
ab6f762f	53	if (printk_percpu_data_ready())
ddb9baa8	54	irq_work_queue(&s->work);
ddb9baa8 SS	55	}
ddb9baa8 SS	56
42a0bb3f	57	/*
099f1c84 SS	58	* Add a message to per-CPU context-dependent buffer. NMI and printk-safe
	59	* have dedicated buffers, because otherwise printk-safe preempted by
	60	* NMI-printk would have overwritten the NMI messages.
	61	*
bc829366	62	* The messages are flushed from irq work (or from panic()), possibly,
099f1c84 SS	63	* from other CPU, concurrently with printk_safe_log_store(). Should this
	64	* happen, printk_safe_log_store() will notice the buffer->len mismatch
	65	* and repeat the write.
42a0bb3f	66	*/
f4e981cb NI	67	static __printf(2, 0) int printk_safe_log_store(struct printk_safe_seq_buf *s,
f4e981cb NI	68	const char *fmt, va_list args)
42a0bb3f	69	{
099f1c84	70	int add;
42a0bb3f	71	size_t len;
988a35f8	72	va_list ap;
42a0bb3f PM	73
	74	again:
	75	len = atomic_read(&s->len);
	76
4a998e32 PM	77	/* The trailing '\0' is not counted into len. */
4a998e32 PM	78	if (len >= sizeof(s->buffer) - 1) {
ddb9baa8 SS	79	atomic_inc(&s->message_lost);
ddb9baa8 SS	80	queue_flush_work(s);
42a0bb3f	81	return 0;
b522deab	82	}
42a0bb3f PM	83
42a0bb3f PM	84	/*
099f1c84 SS	85	* Make sure that all old data have been read before the buffer
099f1c84 SS	86	* was reset. This is not needed when we just append data.
42a0bb3f PM	87	*/
	88	if (!len)
	89	smp_rmb();
	90
988a35f8 TH	91	va_copy(ap, args);
	92	add = vscnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, ap);
	93	va_end(ap);
ddb9baa8 SS	94	if (!add)
ddb9baa8 SS	95	return 0;
42a0bb3f PM	96
	97	/*
	98	* Do it once again if the buffer has been flushed in the meantime.
	99	* Note that atomic_cmpxchg() is an implicit memory barrier that
	100	* makes sure that the data were written before updating s->len.
	101	*/
	102	if (atomic_cmpxchg(&s->len, len, len + add) != len)
	103	goto again;
	104
ddb9baa8	105	queue_flush_work(s);
42a0bb3f PM	106	return add;
	107	}
	108
7acac344	109	static inline void printk_safe_flush_line(const char *text, int len)
42a0bb3f	110	{
cf9b1106	111	/*
7acac344 SS	112	* Avoid any console drivers calls from here, because we may be
	113	* in NMI or printk_safe context (when in panic). The messages
	114	* must go only into the ring buffer at this stage. Consoles will
	115	* get explicitly called later when a crashdump is not generated.
cf9b1106	116	*/
7acac344	117	printk_deferred("%.*s", len, text);
42a0bb3f PM	118	}
42a0bb3f PM	119
22c2c7b2	120	/* printk part of the temporary buffer line by line */
f92bac3b	121	static int printk_safe_flush_buffer(const char *start, size_t len)
19feeff1	122	{
22c2c7b2 PM	123	const char c, end;
	124	bool header;
	125
	126	c = start;
	127	end = start + len;
	128	header = true;
	129
	130	/* Print line by line. */
	131	while (c < end) {
	132	if (*c == '\n') {
f92bac3b	133	printk_safe_flush_line(start, c - start + 1);
22c2c7b2 PM	134	start = ++c;
	135	header = true;
	136	continue;
	137	}
	138
	139	/* Handle continuous lines or missing new line. */
	140	if ((c + 1 < end) && printk_get_level(c)) {
	141	if (header) {
	142	c = printk_skip_level(c);
	143	continue;
	144	}
	145
f92bac3b	146	printk_safe_flush_line(start, c - start);
22c2c7b2 PM	147	start = c++;
	148	header = true;
	149	continue;
	150	}
	151
	152	header = false;
	153	c++;
	154	}
19feeff1	155
22c2c7b2 PM	156	/* Check if there was a partial line. Ignore pure header. */
	157	if (start < end && !header) {
	158	static const char newline[] = KERN_CONT "\n";
	159
f92bac3b SS	160	printk_safe_flush_line(start, end - start);
f92bac3b SS	161	printk_safe_flush_line(newline, strlen(newline));
22c2c7b2 PM	162	}
	163
	164	return len;
19feeff1 SS	165	}
19feeff1 SS	166
ddb9baa8 SS	167	static void report_message_lost(struct printk_safe_seq_buf *s)
	168	{
	169	int lost = atomic_xchg(&s->message_lost, 0);
	170
	171	if (lost)
	172	printk_deferred("Lost %d message(s)!\n", lost);
	173	}
	174
42a0bb3f	175	/*
099f1c84	176	* Flush data from the associated per-CPU buffer. The function
42a0bb3f PM	177	* can be called either via IRQ work or independently.
42a0bb3f PM	178	*/
f92bac3b	179	static void __printk_safe_flush(struct irq_work *work)
42a0bb3f PM	180	{
	181	static raw_spinlock_t read_lock =
	182	__RAW_SPIN_LOCK_INITIALIZER(read_lock);
f92bac3b SS	183	struct printk_safe_seq_buf *s =
f92bac3b SS	184	container_of(work, struct printk_safe_seq_buf, work);
42a0bb3f	185	unsigned long flags;
22c2c7b2 PM	186	size_t len;
22c2c7b2 PM	187	int i;
42a0bb3f PM	188
	189	/*
	190	* The lock has two functions. First, one reader has to flush all
	191	* available message to make the lockless synchronization with
	192	* writers easier. Second, we do not want to mix messages from
	193	* different CPUs. This is especially important when printing
	194	* a backtrace.
	195	*/
	196	raw_spin_lock_irqsave(&read_lock, flags);
	197
	198	i = 0;
	199	more:
	200	len = atomic_read(&s->len);
	201
	202	/*
	203	* This is just a paranoid check that nobody has manipulated
	204	* the buffer an unexpected way. If we printed something then
22c2c7b2 PM	205	* @len must only increase. Also it should never overflow the
22c2c7b2 PM	206	* buffer size.
42a0bb3f	207	*/
22c2c7b2	208	if ((i && i >= len) \|\| len > sizeof(s->buffer)) {
f92bac3b	209	const char *msg = "printk_safe_flush: internal error\n";
19feeff1	210
f92bac3b	211	printk_safe_flush_line(msg, strlen(msg));
22c2c7b2	212	len = 0;
19feeff1	213	}
42a0bb3f PM	214
	215	if (!len)
	216	goto out; /* Someone else has already flushed the buffer. */
	217
	218	/* Make sure that data has been written up to the @len */
	219	smp_rmb();
f92bac3b	220	i += printk_safe_flush_buffer(s->buffer + i, len - i);
42a0bb3f PM	221
	222	/*
	223	* Check that nothing has got added in the meantime and truncate
	224	* the buffer. Note that atomic_cmpxchg() is an implicit memory
	225	* barrier that makes sure that the data were copied before
	226	* updating s->len.
	227	*/
	228	if (atomic_cmpxchg(&s->len, len, 0) != len)
	229	goto more;
	230
	231	out:
ddb9baa8	232	report_message_lost(s);
42a0bb3f PM	233	raw_spin_unlock_irqrestore(&read_lock, flags);
	234	}
	235
	236	/**
f92bac3b	237	* printk_safe_flush - flush all per-cpu nmi buffers.
42a0bb3f PM	238	*
	239	* The buffers are flushed automatically via IRQ work. This function
	240	* is useful only when someone wants to be sure that all buffers have
	241	* been flushed at some point.
	242	*/
f92bac3b	243	void printk_safe_flush(void)
42a0bb3f PM	244	{
	245	int cpu;
	246
099f1c84 SS	247	for_each_possible_cpu(cpu) {
099f1c84 SS	248	#ifdef CONFIG_PRINTK_NMI
f92bac3b	249	__printk_safe_flush(&per_cpu(nmi_print_seq, cpu).work);
099f1c84 SS	250	#endif
	251	__printk_safe_flush(&per_cpu(safe_print_seq, cpu).work);
	252	}
42a0bb3f PM	253	}
42a0bb3f PM	254
cf9b1106	255	/**
f92bac3b	256	* printk_safe_flush_on_panic - flush all per-cpu nmi buffers when the system
cf9b1106 PM	257	* goes down.
cf9b1106 PM	258	*
f92bac3b	259	* Similar to printk_safe_flush() but it can be called even in NMI context when
cf9b1106 PM	260	* the system goes down. It does the best effort to get NMI messages into
	261	* the main ring buffer.
	262	*
	263	* Note that it could try harder when there is only one CPU online.
	264	*/
f92bac3b	265	void printk_safe_flush_on_panic(void)
cf9b1106 PM	266	{
	267	/*
	268	* Make sure that we could access the main ring buffer.
	269	* Do not risk a double release when more CPUs are up.
	270	*/
554755be	271	if (raw_spin_is_locked(&logbuf_lock)) {
cf9b1106 PM	272	if (num_online_cpus() > 1)
	273	return;
	274
	275	debug_locks_off();
	276	raw_spin_lock_init(&logbuf_lock);
	277	}
	278
f92bac3b	279	printk_safe_flush();
cf9b1106 PM	280	}
cf9b1106 PM	281
099f1c84 SS	282	#ifdef CONFIG_PRINTK_NMI
	283	/*
	284	* Safe printk() for NMI context. It uses a per-CPU buffer to
	285	* store the message. NMIs are not nested, so there is always only
	286	* one writer running. But the buffer might get flushed from another
	287	* CPU, so we need to be careful.
	288	*/
f4e981cb	289	static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
099f1c84 SS	290	{
	291	struct printk_safe_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
	292
	293	return printk_safe_log_store(s, fmt, args);
	294	}
	295
d1c392c9	296	void notrace printk_nmi_enter(void)
099f1c84	297	{
03fc7f9c	298	this_cpu_or(printk_context, PRINTK_NMI_CONTEXT_MASK);
099f1c84 SS	299	}
099f1c84 SS	300
d1c392c9	301	void notrace printk_nmi_exit(void)
099f1c84	302	{
03fc7f9c PM	303	this_cpu_and(printk_context, ~PRINTK_NMI_CONTEXT_MASK);
	304	}
	305
	306	/*
	307	* Marks a code that might produce many messages in NMI context
	308	* and the risk of losing them is more critical than eventual
	309	* reordering.
	310	*
	311	* It has effect only when called in NMI context. Then printk()
	312	* will try to store the messages into the main logbuf directly
	313	* and use the per-CPU buffers only as a fallback when the lock
	314	* is not available.
	315	*/
	316	void printk_nmi_direct_enter(void)
	317	{
	318	if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
	319	this_cpu_or(printk_context, PRINTK_NMI_DIRECT_CONTEXT_MASK);
	320	}
	321
	322	void printk_nmi_direct_exit(void)
	323	{
	324	this_cpu_and(printk_context, ~PRINTK_NMI_DIRECT_CONTEXT_MASK);
099f1c84 SS	325	}
	326
	327	#else
	328
f4e981cb	329	static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
099f1c84 SS	330	{
	331	return 0;
	332	}
	333
	334	#endif /* CONFIG_PRINTK_NMI */
	335
	336	/*
	337	* Lock-less printk(), to avoid deadlocks should the printk() recurse
	338	* into itself. It uses a per-CPU buffer to store the message, just like
	339	* NMI.
	340	*/
f4e981cb	341	static __printf(1, 0) int vprintk_safe(const char *fmt, va_list args)
099f1c84 SS	342	{
	343	struct printk_safe_seq_buf *s = this_cpu_ptr(&safe_print_seq);
	344
	345	return printk_safe_log_store(s, fmt, args);
	346	}
	347
	348	/* Can be preempted by NMI. */
	349	void __printk_safe_enter(void)
	350	{
	351	this_cpu_inc(printk_context);
	352	}
	353
	354	/* Can be preempted by NMI. */
	355	void __printk_safe_exit(void)
	356	{
	357	this_cpu_dec(printk_context);
	358	}
	359
	360	__printf(1, 0) int vprintk_func(const char *fmt, va_list args)
	361	{
03fc7f9c PM	362	/*
	363	* Try to use the main logbuf even in NMI. But avoid calling console
	364	* drivers that might have their own locks.
	365	*/
	366	if ((this_cpu_read(printk_context) & PRINTK_NMI_DIRECT_CONTEXT_MASK) &&
	367	raw_spin_trylock(&logbuf_lock)) {
	368	int len;
	369
	370	len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
	371	raw_spin_unlock(&logbuf_lock);
	372	defer_console_output();
	373	return len;
	374	}
	375
719f6a70	376	/* Use extra buffer in NMI when logbuf_lock is taken or in safe mode. */
099f1c84 SS	377	if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
	378	return vprintk_nmi(fmt, args);
	379
719f6a70	380	/* Use extra buffer to prevent a recursion deadlock in safe mode. */
099f1c84 SS	381	if (this_cpu_read(printk_context) & PRINTK_SAFE_CONTEXT_MASK)
	382	return vprintk_safe(fmt, args);
	383
719f6a70	384	/* No obstacles. */
099f1c84 SS	385	return vprintk_default(fmt, args);
	386	}
	387
f92bac3b	388	void __init printk_safe_init(void)
42a0bb3f PM	389	{
	390	int cpu;
	391
	392	for_each_possible_cpu(cpu) {
099f1c84 SS	393	struct printk_safe_seq_buf *s;
	394
	395	s = &per_cpu(safe_print_seq, cpu);
	396	init_irq_work(&s->work, __printk_safe_flush);
42a0bb3f	397
099f1c84 SS	398	#ifdef CONFIG_PRINTK_NMI
099f1c84 SS	399	s = &per_cpu(nmi_print_seq, cpu);
f92bac3b	400	init_irq_work(&s->work, __printk_safe_flush);
099f1c84	401	#endif
42a0bb3f PM	402	}
42a0bb3f PM	403
42a0bb3f	404	/* Flush pending messages that did not have scheduled IRQ works. */
f92bac3b	405	printk_safe_flush();
42a0bb3f	406	}