[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 <linux/kprobes.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 noinstr printk_nmi_enter(void)
{
	this_cpu_add(printk_context, PRINTK_NMI_CONTEXT_OFFSET);
}

void noinstr printk_nmi_exit(void)
{
	this_cpu_sub(printk_context, PRINTK_NMI_CONTEXT_OFFSET);
}

/*
 * 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>
b0f51883	13	#include <linux/kprobes.h>
42a0bb3f PM	14
	15	#include "internal.h"
	16
	17	/*
	18	* printk() could not take logbuf_lock in NMI context. Instead,
	19	* it uses an alternative implementation that temporary stores
	20	* the strings into a per-CPU buffer. The content of the buffer
	21	* is later flushed into the main ring buffer via IRQ work.
	22	*
	23	* The alternative implementation is chosen transparently
099f1c84 SS	24	* by examinig current printk() context mask stored in @printk_context
099f1c84 SS	25	* per-CPU variable.
42a0bb3f PM	26	*
	27	* The implementation allows to flush the strings also from another CPU.
	28	* There are situations when we want to make sure that all buffers
	29	* were handled or when IRQs are blocked.
	30	*/
42a0bb3f	31
f92bac3b	32	#define SAFE_LOG_BUF_LEN ((1 << CONFIG_PRINTK_SAFE_LOG_BUF_SHIFT) - \
ddb9baa8 SS	33	sizeof(atomic_t) - \
	34	sizeof(atomic_t) - \
	35	sizeof(struct irq_work))
42a0bb3f	36
f92bac3b	37	struct printk_safe_seq_buf {
42a0bb3f	38	atomic_t len; /* length of written data */
ddb9baa8	39	atomic_t message_lost;
42a0bb3f	40	struct irq_work work; /* IRQ work that flushes the buffer */
f92bac3b	41	unsigned char buffer[SAFE_LOG_BUF_LEN];
42a0bb3f	42	};
099f1c84 SS	43
	44	static DEFINE_PER_CPU(struct printk_safe_seq_buf, safe_print_seq);
	45	static DEFINE_PER_CPU(int, printk_context);
	46
	47	#ifdef CONFIG_PRINTK_NMI
f92bac3b	48	static DEFINE_PER_CPU(struct printk_safe_seq_buf, nmi_print_seq);
099f1c84	49	#endif
42a0bb3f	50
ddb9baa8 SS	51	/* Get flushed in a more safe context. */
	52	static void queue_flush_work(struct printk_safe_seq_buf *s)
	53	{
ab6f762f	54	if (printk_percpu_data_ready())
ddb9baa8	55	irq_work_queue(&s->work);
ddb9baa8 SS	56	}
ddb9baa8 SS	57
42a0bb3f	58	/*
099f1c84 SS	59	* Add a message to per-CPU context-dependent buffer. NMI and printk-safe
	60	* have dedicated buffers, because otherwise printk-safe preempted by
	61	* NMI-printk would have overwritten the NMI messages.
	62	*
bc829366	63	* The messages are flushed from irq work (or from panic()), possibly,
099f1c84 SS	64	* from other CPU, concurrently with printk_safe_log_store(). Should this
	65	* happen, printk_safe_log_store() will notice the buffer->len mismatch
	66	* and repeat the write.
42a0bb3f	67	*/
f4e981cb NI	68	static __printf(2, 0) int printk_safe_log_store(struct printk_safe_seq_buf *s,
f4e981cb NI	69	const char *fmt, va_list args)
42a0bb3f	70	{
099f1c84	71	int add;
42a0bb3f	72	size_t len;
988a35f8	73	va_list ap;
42a0bb3f PM	74
	75	again:
	76	len = atomic_read(&s->len);
	77
4a998e32 PM	78	/* The trailing '\0' is not counted into len. */
4a998e32 PM	79	if (len >= sizeof(s->buffer) - 1) {
ddb9baa8 SS	80	atomic_inc(&s->message_lost);
ddb9baa8 SS	81	queue_flush_work(s);
42a0bb3f	82	return 0;
b522deab	83	}
42a0bb3f PM	84
42a0bb3f PM	85	/*
099f1c84 SS	86	* Make sure that all old data have been read before the buffer
099f1c84 SS	87	* was reset. This is not needed when we just append data.
42a0bb3f PM	88	*/
	89	if (!len)
	90	smp_rmb();
	91
988a35f8 TH	92	va_copy(ap, args);
	93	add = vscnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, ap);
	94	va_end(ap);
ddb9baa8 SS	95	if (!add)
ddb9baa8 SS	96	return 0;
42a0bb3f PM	97
	98	/*
	99	* Do it once again if the buffer has been flushed in the meantime.
	100	* Note that atomic_cmpxchg() is an implicit memory barrier that
	101	* makes sure that the data were written before updating s->len.
	102	*/
	103	if (atomic_cmpxchg(&s->len, len, len + add) != len)
	104	goto again;
	105
ddb9baa8	106	queue_flush_work(s);
42a0bb3f PM	107	return add;
	108	}
	109
7acac344	110	static inline void printk_safe_flush_line(const char *text, int len)
42a0bb3f	111	{
cf9b1106	112	/*
7acac344 SS	113	* Avoid any console drivers calls from here, because we may be
	114	* in NMI or printk_safe context (when in panic). The messages
	115	* must go only into the ring buffer at this stage. Consoles will
	116	* get explicitly called later when a crashdump is not generated.
cf9b1106	117	*/
7acac344	118	printk_deferred("%.*s", len, text);
42a0bb3f PM	119	}
42a0bb3f PM	120
22c2c7b2	121	/* printk part of the temporary buffer line by line */
f92bac3b	122	static int printk_safe_flush_buffer(const char *start, size_t len)
19feeff1	123	{
22c2c7b2 PM	124	const char c, end;
	125	bool header;
	126
	127	c = start;
	128	end = start + len;
	129	header = true;
	130
	131	/* Print line by line. */
	132	while (c < end) {
	133	if (*c == '\n') {
f92bac3b	134	printk_safe_flush_line(start, c - start + 1);
22c2c7b2 PM	135	start = ++c;
	136	header = true;
	137	continue;
	138	}
	139
	140	/* Handle continuous lines or missing new line. */
	141	if ((c + 1 < end) && printk_get_level(c)) {
	142	if (header) {
	143	c = printk_skip_level(c);
	144	continue;
	145	}
	146
f92bac3b	147	printk_safe_flush_line(start, c - start);
22c2c7b2 PM	148	start = c++;
	149	header = true;
	150	continue;
	151	}
	152
	153	header = false;
	154	c++;
	155	}
19feeff1	156
22c2c7b2 PM	157	/* Check if there was a partial line. Ignore pure header. */
	158	if (start < end && !header) {
	159	static const char newline[] = KERN_CONT "\n";
	160
f92bac3b SS	161	printk_safe_flush_line(start, end - start);
f92bac3b SS	162	printk_safe_flush_line(newline, strlen(newline));
22c2c7b2 PM	163	}
	164
	165	return len;
19feeff1 SS	166	}
19feeff1 SS	167
ddb9baa8 SS	168	static void report_message_lost(struct printk_safe_seq_buf *s)
	169	{
	170	int lost = atomic_xchg(&s->message_lost, 0);
	171
	172	if (lost)
	173	printk_deferred("Lost %d message(s)!\n", lost);
	174	}
	175
42a0bb3f	176	/*
099f1c84	177	* Flush data from the associated per-CPU buffer. The function
42a0bb3f PM	178	* can be called either via IRQ work or independently.
42a0bb3f PM	179	*/
f92bac3b	180	static void __printk_safe_flush(struct irq_work *work)
42a0bb3f PM	181	{
	182	static raw_spinlock_t read_lock =
	183	__RAW_SPIN_LOCK_INITIALIZER(read_lock);
f92bac3b SS	184	struct printk_safe_seq_buf *s =
f92bac3b SS	185	container_of(work, struct printk_safe_seq_buf, work);
42a0bb3f	186	unsigned long flags;
22c2c7b2 PM	187	size_t len;
22c2c7b2 PM	188	int i;
42a0bb3f PM	189
	190	/*
	191	* The lock has two functions. First, one reader has to flush all
	192	* available message to make the lockless synchronization with
	193	* writers easier. Second, we do not want to mix messages from
	194	* different CPUs. This is especially important when printing
	195	* a backtrace.
	196	*/
	197	raw_spin_lock_irqsave(&read_lock, flags);
	198
	199	i = 0;
	200	more:
	201	len = atomic_read(&s->len);
	202
	203	/*
	204	* This is just a paranoid check that nobody has manipulated
	205	* the buffer an unexpected way. If we printed something then
22c2c7b2 PM	206	* @len must only increase. Also it should never overflow the
22c2c7b2 PM	207	* buffer size.
42a0bb3f	208	*/
22c2c7b2	209	if ((i && i >= len) \|\| len > sizeof(s->buffer)) {
f92bac3b	210	const char *msg = "printk_safe_flush: internal error\n";
19feeff1	211
f92bac3b	212	printk_safe_flush_line(msg, strlen(msg));
22c2c7b2	213	len = 0;
19feeff1	214	}
42a0bb3f PM	215
	216	if (!len)
	217	goto out; /* Someone else has already flushed the buffer. */
	218
	219	/* Make sure that data has been written up to the @len */
	220	smp_rmb();
f92bac3b	221	i += printk_safe_flush_buffer(s->buffer + i, len - i);
42a0bb3f PM	222
	223	/*
	224	* Check that nothing has got added in the meantime and truncate
	225	* the buffer. Note that atomic_cmpxchg() is an implicit memory
	226	* barrier that makes sure that the data were copied before
	227	* updating s->len.
	228	*/
	229	if (atomic_cmpxchg(&s->len, len, 0) != len)
	230	goto more;
	231
	232	out:
ddb9baa8	233	report_message_lost(s);
42a0bb3f PM	234	raw_spin_unlock_irqrestore(&read_lock, flags);
	235	}
	236
	237	/**
f92bac3b	238	* printk_safe_flush - flush all per-cpu nmi buffers.
42a0bb3f PM	239	*
	240	* The buffers are flushed automatically via IRQ work. This function
	241	* is useful only when someone wants to be sure that all buffers have
	242	* been flushed at some point.
	243	*/
f92bac3b	244	void printk_safe_flush(void)
42a0bb3f PM	245	{
	246	int cpu;
	247
099f1c84 SS	248	for_each_possible_cpu(cpu) {
099f1c84 SS	249	#ifdef CONFIG_PRINTK_NMI
f92bac3b	250	__printk_safe_flush(&per_cpu(nmi_print_seq, cpu).work);
099f1c84 SS	251	#endif
	252	__printk_safe_flush(&per_cpu(safe_print_seq, cpu).work);
	253	}
42a0bb3f PM	254	}
42a0bb3f PM	255
cf9b1106	256	/**
f92bac3b	257	* printk_safe_flush_on_panic - flush all per-cpu nmi buffers when the system
cf9b1106 PM	258	* goes down.
cf9b1106 PM	259	*
f92bac3b	260	* Similar to printk_safe_flush() but it can be called even in NMI context when
cf9b1106 PM	261	* the system goes down. It does the best effort to get NMI messages into
	262	* the main ring buffer.
	263	*
	264	* Note that it could try harder when there is only one CPU online.
	265	*/
f92bac3b	266	void printk_safe_flush_on_panic(void)
cf9b1106 PM	267	{
	268	/*
	269	* Make sure that we could access the main ring buffer.
	270	* Do not risk a double release when more CPUs are up.
	271	*/
554755be	272	if (raw_spin_is_locked(&logbuf_lock)) {
cf9b1106 PM	273	if (num_online_cpus() > 1)
	274	return;
	275
	276	debug_locks_off();
	277	raw_spin_lock_init(&logbuf_lock);
	278	}
	279
f92bac3b	280	printk_safe_flush();
cf9b1106 PM	281	}
cf9b1106 PM	282
099f1c84 SS	283	#ifdef CONFIG_PRINTK_NMI
	284	/*
	285	* Safe printk() for NMI context. It uses a per-CPU buffer to
	286	* store the message. NMIs are not nested, so there is always only
	287	* one writer running. But the buffer might get flushed from another
	288	* CPU, so we need to be careful.
	289	*/
f4e981cb	290	static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
099f1c84 SS	291	{
	292	struct printk_safe_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
	293
	294	return printk_safe_log_store(s, fmt, args);
	295	}
	296
b0f51883	297	void noinstr printk_nmi_enter(void)
099f1c84	298	{
8c4e93c3	299	this_cpu_add(printk_context, PRINTK_NMI_CONTEXT_OFFSET);
099f1c84 SS	300	}
099f1c84 SS	301
b0f51883	302	void noinstr printk_nmi_exit(void)
099f1c84	303	{
8c4e93c3	304	this_cpu_sub(printk_context, PRINTK_NMI_CONTEXT_OFFSET);
03fc7f9c PM	305	}
	306
	307	/*
	308	* Marks a code that might produce many messages in NMI context
	309	* and the risk of losing them is more critical than eventual
	310	* reordering.
	311	*
	312	* It has effect only when called in NMI context. Then printk()
	313	* will try to store the messages into the main logbuf directly
	314	* and use the per-CPU buffers only as a fallback when the lock
	315	* is not available.
	316	*/
	317	void printk_nmi_direct_enter(void)
	318	{
	319	if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
	320	this_cpu_or(printk_context, PRINTK_NMI_DIRECT_CONTEXT_MASK);
	321	}
	322
	323	void printk_nmi_direct_exit(void)
	324	{
	325	this_cpu_and(printk_context, ~PRINTK_NMI_DIRECT_CONTEXT_MASK);
099f1c84 SS	326	}
	327
	328	#else
	329
f4e981cb	330	static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
099f1c84 SS	331	{
	332	return 0;
	333	}
	334
	335	#endif /* CONFIG_PRINTK_NMI */
	336
	337	/*
	338	* Lock-less printk(), to avoid deadlocks should the printk() recurse
	339	* into itself. It uses a per-CPU buffer to store the message, just like
	340	* NMI.
	341	*/
f4e981cb	342	static __printf(1, 0) int vprintk_safe(const char *fmt, va_list args)
099f1c84 SS	343	{
	344	struct printk_safe_seq_buf *s = this_cpu_ptr(&safe_print_seq);
	345
	346	return printk_safe_log_store(s, fmt, args);
	347	}
	348
	349	/* Can be preempted by NMI. */
	350	void __printk_safe_enter(void)
	351	{
	352	this_cpu_inc(printk_context);
	353	}
	354
	355	/* Can be preempted by NMI. */
	356	void __printk_safe_exit(void)
	357	{
	358	this_cpu_dec(printk_context);
	359	}
	360
	361	__printf(1, 0) int vprintk_func(const char *fmt, va_list args)
	362	{
03fc7f9c PM	363	/*
	364	* Try to use the main logbuf even in NMI. But avoid calling console
	365	* drivers that might have their own locks.
	366	*/
	367	if ((this_cpu_read(printk_context) & PRINTK_NMI_DIRECT_CONTEXT_MASK) &&
	368	raw_spin_trylock(&logbuf_lock)) {
	369	int len;
	370
	371	len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
	372	raw_spin_unlock(&logbuf_lock);
	373	defer_console_output();
	374	return len;
	375	}
	376
719f6a70	377	/* Use extra buffer in NMI when logbuf_lock is taken or in safe mode. */
099f1c84 SS	378	if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
	379	return vprintk_nmi(fmt, args);
	380
719f6a70	381	/* Use extra buffer to prevent a recursion deadlock in safe mode. */
099f1c84 SS	382	if (this_cpu_read(printk_context) & PRINTK_SAFE_CONTEXT_MASK)
	383	return vprintk_safe(fmt, args);
	384
719f6a70	385	/* No obstacles. */
099f1c84 SS	386	return vprintk_default(fmt, args);
	387	}
	388
f92bac3b	389	void __init printk_safe_init(void)
42a0bb3f PM	390	{
	391	int cpu;
	392
	393	for_each_possible_cpu(cpu) {
099f1c84 SS	394	struct printk_safe_seq_buf *s;
	395
	396	s = &per_cpu(safe_print_seq, cpu);
	397	init_irq_work(&s->work, __printk_safe_flush);
42a0bb3f	398
099f1c84 SS	399	#ifdef CONFIG_PRINTK_NMI
099f1c84 SS	400	s = &per_cpu(nmi_print_seq, cpu);
f92bac3b	401	init_irq_work(&s->work, __printk_safe_flush);
099f1c84	402	#endif
42a0bb3f PM	403	}
42a0bb3f PM	404
42a0bb3f	405	/* Flush pending messages that did not have scheduled IRQ works. */
f92bac3b	406	printk_safe_flush();
42a0bb3f	407	}