litmus-rt.git - The LITMUS^RT kernel.

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The LITMUS^RT kernel.

Bjoern Brandenburg

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/*
 *  linux/kernel/printk.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 * Modified to make sys_syslog() more flexible: added commands to
 * return the last 4k of kernel messages, regardless of whether
 * they've been read or not.  Added option to suppress kernel printk's
 * to the console.  Added hook for sending the console messages
 * elsewhere, in preparation for a serial line console (someday).
 * Ted Ts'o, 2/11/93.
 * Modified for sysctl support, 1/8/97, Chris Horn.
 * Fixed SMP synchronization, 08/08/99, Manfred Spraul
 *     manfred@colorfullife.com
 * Rewrote bits to get rid of console_lock
 *	01Mar01 Andrew Morton
 */

#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/tty.h>
#include <linux/tty_driver.h>
#include <linux/console.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/nmi.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/interrupt.h>			/* For in_interrupt() */
#include <linux/delay.h>
#include <linux/smp.h>
#include <linux/security.h>
#include <linux/bootmem.h>
#include <linux/memblock.h>
#include <linux/syscalls.h>
#include <linux/kexec.h>
#include <linux/kdb.h>
#include <linux/ratelimit.h>
#include <linux/kmsg_dump.h>
#include <linux/syslog.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <linux/rculist.h>

#include <asm/uaccess.h>

#define CREATE_TRACE_POINTS
#include <trace/events/printk.h>

/*
 * Architectures can override it:
 */
void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
{
}

#define __LOG_BUF_LEN	(1 << CONFIG_LOG_BUF_SHIFT)

/* printk's without a loglevel use this.. */
#define DEFAULT_MESSAGE_LOGLEVEL CONFIG_DEFAULT_MESSAGE_LOGLEVEL

/* We show everything that is MORE important than this.. */
#define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
#define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */

DECLARE_WAIT_QUEUE_HEAD(log_wait);

int console_printk[4] = {
	DEFAULT_CONSOLE_LOGLEVEL,	/* console_loglevel */
	DEFAULT_MESSAGE_LOGLEVEL,	/* default_message_loglevel */
	MINIMUM_CONSOLE_LOGLEVEL,	/* minimum_console_loglevel */
	DEFAULT_CONSOLE_LOGLEVEL,	/* default_console_loglevel */
};

/*
 * Low level drivers may need that to know if they can schedule in
 * their unblank() callback or not. So let's export it.
 */
int oops_in_progress;
EXPORT_SYMBOL(oops_in_progress);

/*
 * console_sem protects the console_drivers list, and also
 * provides serialisation for access to the entire console
 * driver system.
 */
static DEFINE_SEMAPHORE(console_sem);
struct console *console_drivers;
EXPORT_SYMBOL_GPL(console_drivers);

/*
 * This is used for debugging the mess that is the VT code by
 * keeping track if we have the console semaphore held. It's
 * definitely not the perfect debug tool (we don't know if _WE_
 * hold it are racing, but it helps tracking those weird code
 * path in the console code where we end up in places I want
 * locked without the console sempahore held
 */
static int console_locked, console_suspended;

/*
 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
 * It is also used in interesting ways to provide interlocking in
 * console_unlock();.
 */
static DEFINE_RAW_SPINLOCK(logbuf_lock);

#define LOG_BUF_MASK (log_buf_len-1)
#define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])

/*
 * The indices into log_buf are not constrained to log_buf_len - they
 * must be masked before subscripting
 */
static unsigned log_start;	/* Index into log_buf: next char to be read by syslog() */
static unsigned con_start;	/* Index into log_buf: next char to be sent to consoles */
static unsigned log_end;	/* Index into log_buf: most-recently-written-char + 1 */

/*
 * If exclusive_console is non-NULL then only this console is to be printed to.
 */
static struct console *exclusive_console;

/*
 *	Array of consoles built from command line options (console=)
 */
struct console_cmdline
{
	char	name[8];			/* Name of the driver	    */
	int	index;				/* Minor dev. to use	    */
	char	*options;			/* Options for the driver   */
#ifdef CONFIG_A11Y_BRAILLE_CONSOLE
	char	*brl_options;			/* Options for braille driver */
#endif
};

#define MAX_CMDLINECONSOLES 8

static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
static int selected_console = -1;
static int preferred_console = -1;
int console_set_on_cmdline;
EXPORT_SYMBOL(console_set_on_cmdline);

/* Flag: console code may call schedule() */
static int console_may_schedule;

#ifdef CONFIG_PRINTK

static char __log_buf[__LOG_BUF_LEN];
static char *log_buf = __log_buf;
static int log_buf_len = __LOG_BUF_LEN;
static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
static int saved_console_loglevel = -1;

#ifdef CONFIG_KEXEC
/*
 * This appends the listed symbols to /proc/vmcoreinfo
 *
 * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
 * obtain access to symbols that are otherwise very difficult to locate.  These
 * symbols are specifically used so that utilities can access and extract the
 * dmesg log from a vmcore file after a crash.
 */
void log_buf_kexec_setup(void)
{
	VMCOREINFO_SYMBOL(log_buf);
	VMCOREINFO_SYMBOL(log_end);
	VMCOREINFO_SYMBOL(log_buf_len);
	VMCOREINFO_SYMBOL(logged_chars);
}
#endif

/* requested log_buf_len from kernel cmdline */
static unsigned long __initdata new_log_buf_len;

/* save requested log_buf_len since it's too early to process it */
static int __init log_buf_len_setup(char *str)
{
	unsigned size = memparse(str, &str);

	if (size)
		size = roundup_pow_of_two(size);
	if (size > log_buf_len)
		new_log_buf_len = size;

	return 0;
}
early_param("log_buf_len", log_buf_len_setup);

void __init setup_log_buf(int early)
{
	unsigned long flags;
	unsigned start, dest_idx, offset;
	char *new_log_buf;
	int free;

	if (!new_log_buf_len)
		return;

	if (early) {
		unsigned long mem;

		mem = memblock_alloc(new_log_buf_len, PAGE_SIZE);
		if (!mem)
			return;
		new_log_buf = __va(mem);
	} else {
		new_log_buf = alloc_bootmem_nopanic(new_log_buf_len);
	}

	if (unlikely(!new_log_buf)) {
		pr_err("log_buf_len: %ld bytes not available\n",
			new_log_buf_len);
		return;
	}

	raw_spin_lock_irqsave(&logbuf_lock, flags);
	log_buf_len = new_log_buf_len;
	log_buf = new_log_buf;
	new_log_buf_len = 0;
	free = __LOG_BUF_LEN - log_end;

	offset = start = min(con_start, log_start);
	dest_idx = 0;
	while (start != log_end) {
		unsigned log_idx_mask = start & (__LOG_BUF_LEN - 1);

		log_buf[dest_idx] = __log_buf[log_idx_mask];
		start++;
		dest_idx++;
	}
	log_start -= offset;
	con_start -= offset;
	log_end -= offset;
	raw_spin_unlock_irqrestore(&logbuf_lock, flags);

	pr_info("log_buf_len: %d\n", log_buf_len);
	pr_info("early log buf free: %d(%d%%)\n",
		free, (free * 100) / __LOG_BUF_LEN);
}

#ifdef CONFIG_BOOT_PRINTK_DELAY

static int boot_delay; /* msecs delay after each printk during bootup */
static unsigned long long loops_per_msec;	/* based on boot_delay */

static int __init boot_delay_setup(char *str)
{
	unsigned long lpj;

	lpj = preset_lpj ? preset_lpj : 1000000;	/* some guess */
	loops_per_msec = (unsigned long long)lpj / 1000 * HZ;

	get_option(&str, &boot_delay);
	if (boot_delay > 10 * 1000)
		boot_delay = 0;

	pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
		"HZ: %d, loops_per_msec: %llu\n",
		boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
	return 1;
}
__setup("boot_delay=", boot_delay_setup);

static void boot_delay_msec(void)
{
	unsigned long long k;
	unsigned long timeout;

	if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
		return;

	k = (unsigned long long)loops_per_msec * boot_delay;

	timeout = jiffies + msecs_to_jiffies(boot_delay);
	while (k) {
		k--;
		cpu_relax();
		/*
		 * use (volatile) jiffies to prevent
		 * compiler reduction; loop termination via jiffies
		 * is secondary and may or may not happen.
		 */
		if (time_after(jiffies, timeout))
			break;
		touch_nmi_watchdog();
	}
}
#else
static inline void boot_delay_msec(void)
{
}
#endif

#ifdef CONFIG_SECURITY_DMESG_RESTRICT
int dmesg_restrict = 1;
#else
int dmesg_restrict;
#endif

static int syslog_action_restricted(int type)
{
	if (dmesg_restrict)
		return 1;
	/* Unless restricted, we allow "read all" and "get buffer size" for everybody */
	return type != SYSLOG_ACTION_READ_ALL && type != SYSLOG_ACTION_SIZE_BUFFER;
}

static int check_syslog_permissions(int type, bool from_file)
{
	/*
	 * If this is from /proc/kmsg and we've already opened it, then we've
	 * already done the capabilities checks at open time.
	 */
	if (from_file && type != SYSLOG_ACTION_OPEN)
		return 0;

	if (syslog_action_restricted(type)) {
		if (capable(CAP_SYSLOG))
			return 0;
		/* For historical reasons, accept CAP_SYS_ADMIN too, with a warning */
		if (capable(CAP_SYS_ADMIN)) {
			printk_once(KERN_WARNING "%s (%d): "
				 "Attempt to access syslog with CAP_SYS_ADMIN "
				 "but no CAP_SYSLOG (deprecated).\n",
				 current->comm, task_pid_nr(current));
			return 0;
		}
		return -EPERM;
	}
	return 0;
}

int do_syslog(int type, char __user *buf, int len, bool from_file)
{
	unsigned i, j, limit, count;
	int do_clear = 0;
	char c;
	int error;

	error = check_syslog_permissions(type, from_file);
	if (error)
		goto out;

	error = security_syslog(type);
	if (error)
		return error;

	switch (type) {
	case SYSLOG_ACTION_CLOSE:	/* Close log */
		break;
	case SYSLOG_ACTION_OPEN:	/* Open log */
		break;
	case SYSLOG_ACTION_READ:	/* Read from log */
		error = -EINVAL;
		if (!buf || len < 0)
			goto out;
		error = 0;
		if (!len)
			goto out;
		if (!access_ok(VERIFY_WRITE, buf, len)) {
			error = -EFAULT;
			goto out;
		}
		error = wait_event_interruptible(log_wait,
							(log_start - log_end));
		if (error)
			goto out;
		i = 0;
		raw_spin_lock_irq(&logbuf_lock);
		while (!error && (log_start != log_end) && i < len) {
			c = LOG_BUF(log_start);
			log_start++;
			raw_spin_unlock_irq(&logbuf_lock);
			error = __put_user(c,buf);
			buf++;
			i++;
			cond_resched();
			raw_spin_lock_irq(&logbuf_lock);
		}
		raw_spin_unlock_irq(&logbuf_lock);
		if (!error)
			error = i;
		break;
	/* Read/clear last kernel messages */
	case SYSLOG_ACTION_READ_CLEAR:
		do_clear = 1;
		/* FALL THRU */
	/* Read last kernel messages */
	case SYSLOG_ACTION_READ_ALL:
		error = -EINVAL;
		if (!buf || len < 0)
			goto out;
		error = 0;
		if (!len)
			goto out;
		if (!access_ok(VERIFY_WRITE, buf, len)) {
			error = -EFAULT;
			goto out;
		}
		count = len;
		if (count > log_buf_len)
			count = log_buf_len;
		raw_spin_lock_irq(&logbuf_lock);
		if (count > logged_chars)
			count = logged_chars;
		if (do_clear)
			logged_chars = 0;
		limit = log_end;
		/*
		 * __put_user() could sleep, and while we sleep
		 * printk() could overwrite the messages
		 * we try to copy to user space. Therefore
		 * the messages are copied in reverse. <manfreds>
		 */
		for (i = 0; i < count && !error; i++) {
			j = limit-1-i;
			if (j + log_buf_len < log_end)
				break;
			c = LOG_BUF(j);
			raw_spin_unlock_irq(&logbuf_lock);
			error = __put_user(c,&buf[count-1-i]);
			cond_resched();
			raw_spin_lock_irq(&logbuf_lock);
		}
		raw_spin_unlock_irq(&logbuf_lock);
		if (error)
			break;
		error = i;
		if (i != count) {
			int offset = count-error;
			/* buffer overflow during copy, correct user buffer. */
			for (i = 0; i < error; i++) {
				if (__get_user(c,&buf[i+offset]) ||
				    __put_user(c,&buf[i])) {
					error = -EFAULT;
					break;
				}
				cond_resched();
			}
		}
		break;
	/* Clear ring buffer */
	case SYSLOG_ACTION_CLEAR:
		logged_chars = 0;
		break;
	/* Disable logging to console */
	case SYSLOG_ACTION_CONSOLE_OFF:
		if (saved_console_loglevel == -1)
			saved_console_loglevel = console_loglevel;
		console_loglevel = minimum_console_loglevel;
		break;
	/* Enable logging to console */
	case SYSLOG_ACTION_CONSOLE_ON:
		if (saved_console_loglevel != -1) {
			console_loglevel = saved_console_loglevel;
			saved_console_loglevel = -1;
		}
		break;
	/* Set level of messages printed to console */
	case SYSLOG_ACTION_CONSOLE_LEVEL:
		error = -EINVAL;
		if (len < 1 || len > 8)
			goto out;
		if (len < minimum_console_loglevel)
			len = minimum_console_loglevel;
		console_loglevel = len;
		/* Implicitly re-enable logging to console */
		saved_console_loglevel = -1;
		error = 0;
		break;
	/* Number of chars in the log buffer */
	case SYSLOG_ACTION_SIZE_UNREAD:
		error = log_end - log_start;
		break;
	/* Size of the log buffer */
	case SYSLOG_ACTION_SIZE_BUFFER:
		error = log_buf_len;
		break;
	default:
		error = -EINVAL;
		break;
	}
out:
	return error;
}

SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
{
	return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
}

#ifdef	CONFIG_KGDB_KDB
/* kdb dmesg command needs access to the syslog buffer.  do_syslog()
 * uses locks so it cannot be used during debugging.  Just tell kdb
 * where the start and end of the physical and logical logs are.  This
 * is equivalent to do_syslog(3).
 */
void kdb_syslog_data(char *syslog_data[4])
{
	syslog_data[0] = log_buf;
	syslog_data[1] = log_buf + log_buf_len;
	syslog_data[2] = log_buf + log_end -
		(logged_chars < log_buf_len ? logged_chars : log_buf_len);
	syslog_data[3] = log_buf + log_end;
}
#endif	/* CONFIG_KGDB_KDB */

/*
 * Call the console drivers on a range of log_buf
 */
static void __call_console_drivers(unsigned start, unsigned end)
{
	struct console *con;

	for_each_console(con) {
		if (exclusive_console && con != exclusive_console)
			continue;
		if ((con->flags & CON_ENABLED) && con->write &&
				(cpu_online(smp_processor_id()) ||
				(con->flags & CON_ANYTIME)))
			con->write(con, &LOG_BUF(start), end - start);
	}
}

static bool __read_mostly ignore_loglevel;

static int __init ignore_loglevel_setup(char *str)
{
	ignore_loglevel = 1;
	printk(KERN_INFO "debug: ignoring loglevel setting.\n");

	return 0;
}

early_param("ignore_loglevel", ignore_loglevel_setup);
module_param(ignore_loglevel, bool, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(ignore_loglevel, "ignore loglevel setting, to"
	"print all kernel messages to the console.");

/*
 * Write out chars from start to end - 1 inclusive
 */
static void _call_console_drivers(unsigned start,
				unsigned end, int msg_log_level)
{
	trace_console(&LOG_BUF(0), start, end, log_buf_len);

	if ((msg_log_level < console_loglevel || ignore_loglevel) &&
			console_drivers && start != end) {
		if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
			/* wrapped write */
			__call_console_drivers(start & LOG_BUF_MASK,
						log_buf_len);
			__call_console_drivers(0, end & LOG_BUF_MASK);
		} else {
			__call_console_drivers(start, end);
		}
	}
}

/*
 * Parse the syslog header <[0-9]*>. The decimal value represents 32bit, the
 * lower 3 bit are the log level, the rest are the log facility. In case
 * userspace passes usual userspace syslog messages to /dev/kmsg or
 * /dev/ttyprintk, the log prefix might contain the facility. Printk needs
 * to extract the correct log level for in-kernel processing, and not mangle
 * the original value.
 *
 * If a prefix is found, the length of the prefix is returned. If 'level' is
 * passed, it will be filled in with the log level without a possible facility
 * value. If 'special' is passed, the special printk prefix chars are accepted
 * and returned. If no valid header is found, 0 is returned and the passed
 * variables are not touched.
 */
static size_t log_prefix(const char *p, unsigned int *level, char *special)
{
	unsigned int lev = 0;
	char sp = '\0';
	size_t len;

	if (p[0] != '<' || !p[1])
		return 0;
	if (p[2] == '>') {
		/* usual single digit level number or special char */
		switch (p[1]) {
		case '0' ... '7':
			lev = p[1] - '0';
			break;
		case 'c': /* KERN_CONT */
		case 'd': /* KERN_DEFAULT */
			sp = p[1];
			break;
		default:
			return 0;
		}
		len = 3;
	} else {
		/* multi digit including the level and facility number */
		char *endp = NULL;

		lev = (simple_strtoul(&p[1], &endp, 10) & 7);
		if (endp == NULL || endp[0] != '>')
			return 0;
		len = (endp + 1) - p;
	}

	/* do not accept special char if not asked for */
	if (sp && !special)
		return 0;

	if (special) {
		*special = sp;
		/* return special char, do not touch level */
		if (sp)
			return len;
	}

	if (level)
		*level = lev;
	return len;
}

/*
 * Call the console drivers, asking them to write out
 * log_buf[start] to log_buf[end - 1].
 * The console_lock must be held.
 */
static void call_console_drivers(unsigned start, unsigned end)
{
	unsigned cur_index, start_print;
	static int msg_level = -1;

	BUG_ON(((int)(start - end)) > 0);

	cur_index = start;
	start_print = start;
	while (cur_index != end) {
		if (msg_level < 0 && ((end - cur_index) > 2)) {
			/* strip log prefix */
			cur_index += log_prefix(&LOG_BUF(cur_index), &msg_level, NULL);
			start_print = cur_index;
		}
		while (cur_index != end) {
			char c = LOG_BUF(cur_index);

			cur_index++;
			if (c == '\n') {
				if (msg_level < 0) {
					/*
					 * printk() has already given us loglevel tags in
					 * the buffer.  This code is here in case the
					 * log buffer has wrapped right round and scribbled
					 * on those tags
					 */
					msg_level = default_message_loglevel;
				}
				_call_console_drivers(start_print, cur_index, msg_level);
				msg_level = -1;
				start_print = cur_index;
				break;
			}
		}
	}
	_call_console_drivers(start_print, end, msg_level);
}

static void emit_log_char(char c)
{
	LOG_BUF(log_end) = c;
	log_end++;
	if (log_end - log_start > log_buf_len)
		log_start = log_end - log_buf_len;
	if (log_end - con_start > log_buf_len)
		con_start = log_end - log_buf_len;
	if (logged_chars < log_buf_len)
		logged_chars++;
}

/*
 * Zap console related locks when oopsing. Only zap at most once
 * every 10 seconds, to leave time for slow consoles to print a
 * full oops.
 */
static void zap_locks(void)
{
	static unsigned long oops_timestamp;

	if (time_after_eq(jiffies, oops_timestamp) &&
			!time_after(jiffies, oops_timestamp + 30 * HZ))
		return;

	oops_timestamp = jiffies;

	debug_locks_off();
	/* If a crash is occurring, make sure we can't deadlock */
	raw_spin_lock_init(&logbuf_lock);
	/* And make sure that we print immediately */
	sema_init(&console_sem, 1);
}

#if defined(CONFIG_PRINTK_TIME)
static bool printk_time = 1;
#else
static bool printk_time = 0;
#endif
module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);

static bool always_kmsg_dump;
module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);

/* Check if we have any console registered that can be called early in boot. */
static int have_callable_console(void)
{
	struct console *con;

	for_each_console(con)
		if (con->flags & CON_ANYTIME)
			return 1;

	return 0;
}

/**
 * printk - print a kernel message
 * @fmt: format string
 *
 * This is printk().  It can be called from any context.  We want it to work.
 *
 * We try to grab the console_lock.  If we succeed, it's easy - we log the output and
 * call the console drivers.  If we fail to get the semaphore we place the output
 * into the log buffer and return.  The current holder of the console_sem will
 * notice the new output in console_unlock(); and will send it to the
 * consoles before releasing the lock.
 *


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