linux/kernel/printk.c
Arve Hjønnevåg 403f307576 PM: Fix suspend_console and resume_console to use only one semaphore
This fixes a race where a thread acquires the console while the
console is suspended, and the console is resumed before this
thread releases it. In this case, the secondary console
semaphore would be left locked, and the primary semaphore would
be released twice. This in turn would cause the console switch
on suspend or resume to hang forever.

Note that suspend_console does not actually lock the console
for clients that use acquire_console_sem, it only locks it for
clients that use try_acquire_console_sem. If we change
suspend_console to fully lock the console, then the kernel
may deadlock on suspend. One client of try_acquire_console_sem
is acquire_console_semaphore_for_printk, which uses it to
prevent printk from using the console while it is suspended.

Signed-off-by: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Len Brown <lenb@kernel.org>
Cc: Greg KH <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-02-21 14:17:18 -08:00

1303 lines
32 KiB
C

/*
* 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/syscalls.h>
#include <asm/uaccess.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 4 /* KERN_WARNING */
/* 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 DECLARE_MUTEX(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
* release_console_sem().
*/
static DEFINE_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 */
/*
* 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 __init log_buf_len_setup(char *str)
{
unsigned size = memparse(str, &str);
unsigned long flags;
if (size)
size = roundup_pow_of_two(size);
if (size > log_buf_len) {
unsigned start, dest_idx, offset;
char *new_log_buf;
new_log_buf = alloc_bootmem(size);
if (!new_log_buf) {
printk(KERN_WARNING "log_buf_len: allocation failed\n");
goto out;
}
spin_lock_irqsave(&logbuf_lock, flags);
log_buf_len = size;
log_buf = new_log_buf;
offset = start = min(con_start, log_start);
dest_idx = 0;
while (start != log_end) {
log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
start++;
dest_idx++;
}
log_start -= offset;
con_start -= offset;
log_end -= offset;
spin_unlock_irqrestore(&logbuf_lock, flags);
printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
}
out:
return 1;
}
__setup("log_buf_len=", log_buf_len_setup);
#ifdef CONFIG_BOOT_PRINTK_DELAY
static unsigned int boot_delay; /* msecs delay after each printk during bootup */
static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
static int __init boot_delay_setup(char *str)
{
unsigned long lpj;
unsigned long long loops_per_msec;
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;
printk_delay_msec = loops_per_msec;
printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
"HZ: %d, printk_delay_msec: %llu\n",
boot_delay, preset_lpj, lpj, HZ, printk_delay_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)printk_delay_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
/*
* Commands to do_syslog:
*
* 0 -- Close the log. Currently a NOP.
* 1 -- Open the log. Currently a NOP.
* 2 -- Read from the log.
* 3 -- Read all messages remaining in the ring buffer.
* 4 -- Read and clear all messages remaining in the ring buffer
* 5 -- Clear ring buffer.
* 6 -- Disable printk's to console
* 7 -- Enable printk's to console
* 8 -- Set level of messages printed to console
* 9 -- Return number of unread characters in the log buffer
* 10 -- Return size of the log buffer
*/
int do_syslog(int type, char __user *buf, int len)
{
unsigned i, j, limit, count;
int do_clear = 0;
char c;
int error = 0;
error = security_syslog(type);
if (error)
return error;
switch (type) {
case 0: /* Close log */
break;
case 1: /* Open log */
break;
case 2: /* 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;
spin_lock_irq(&logbuf_lock);
while (!error && (log_start != log_end) && i < len) {
c = LOG_BUF(log_start);
log_start++;
spin_unlock_irq(&logbuf_lock);
error = __put_user(c,buf);
buf++;
i++;
cond_resched();
spin_lock_irq(&logbuf_lock);
}
spin_unlock_irq(&logbuf_lock);
if (!error)
error = i;
break;
case 4: /* Read/clear last kernel messages */
do_clear = 1;
/* FALL THRU */
case 3: /* Read last kernel messages */
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;
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);
spin_unlock_irq(&logbuf_lock);
error = __put_user(c,&buf[count-1-i]);
cond_resched();
spin_lock_irq(&logbuf_lock);
}
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;
case 5: /* Clear ring buffer */
logged_chars = 0;
break;
case 6: /* Disable logging to console */
console_loglevel = minimum_console_loglevel;
break;
case 7: /* Enable logging to console */
console_loglevel = default_console_loglevel;
break;
case 8: /* Set level of messages printed to console */
error = -EINVAL;
if (len < 1 || len > 8)
goto out;
if (len < minimum_console_loglevel)
len = minimum_console_loglevel;
console_loglevel = len;
error = 0;
break;
case 9: /* Number of chars in the log buffer */
error = log_end - log_start;
break;
case 10: /* Size of the log 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);
}
/*
* Call the console drivers on a range of log_buf
*/
static void __call_console_drivers(unsigned start, unsigned end)
{
struct console *con;
for (con = console_drivers; con; con = con->next) {
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 int __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);
/*
* Write out chars from start to end - 1 inclusive
*/
static void _call_console_drivers(unsigned start,
unsigned end, int msg_log_level)
{
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);
}
}
}
/*
* Call the console drivers, asking them to write out
* log_buf[start] to log_buf[end - 1].
* The console_sem 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) &&
LOG_BUF(cur_index + 0) == '<' &&
LOG_BUF(cur_index + 1) >= '0' &&
LOG_BUF(cur_index + 1) <= '7' &&
LOG_BUF(cur_index + 2) == '>') {
msg_level = LOG_BUF(cur_index + 1) - '0';
cur_index += 3;
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;
/* If a crash is occurring, make sure we can't deadlock */
spin_lock_init(&logbuf_lock);
/* And make sure that we print immediately */
init_MUTEX(&console_sem);
}
#if defined(CONFIG_PRINTK_TIME)
static int printk_time = 1;
#else
static int printk_time = 0;
#endif
module_param_named(time, printk_time, 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 (con = console_drivers; con; con = con->next)
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_sem. 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 release_console_sem() and will send it to the
* consoles before releasing the semaphore.
*
* One effect of this deferred printing is that code which calls printk() and
* then changes console_loglevel may break. This is because console_loglevel
* is inspected when the actual printing occurs.
*
* See also:
* printf(3)
*
* See the vsnprintf() documentation for format string extensions over C99.
*/
asmlinkage int printk(const char *fmt, ...)
{
va_list args;
int r;
va_start(args, fmt);
r = vprintk(fmt, args);
va_end(args);
return r;
}
/* cpu currently holding logbuf_lock */
static volatile unsigned int printk_cpu = UINT_MAX;
/*
* Can we actually use the console at this time on this cpu?
*
* Console drivers may assume that per-cpu resources have
* been allocated. So unless they're explicitly marked as
* being able to cope (CON_ANYTIME) don't call them until
* this CPU is officially up.
*/
static inline int can_use_console(unsigned int cpu)
{
return cpu_online(cpu) || have_callable_console();
}
/*
* Try to get console ownership to actually show the kernel
* messages from a 'printk'. Return true (and with the
* console_semaphore held, and 'console_locked' set) if it
* is successful, false otherwise.
*
* This gets called with the 'logbuf_lock' spinlock held and
* interrupts disabled. It should return with 'lockbuf_lock'
* released but interrupts still disabled.
*/
static int acquire_console_semaphore_for_printk(unsigned int cpu)
{
int retval = 0;
if (!try_acquire_console_sem()) {
retval = 1;
/*
* If we can't use the console, we need to release
* the console semaphore by hand to avoid flushing
* the buffer. We need to hold the console semaphore
* in order to do this test safely.
*/
if (!can_use_console(cpu)) {
console_locked = 0;
up(&console_sem);
retval = 0;
}
}
printk_cpu = UINT_MAX;
spin_unlock(&logbuf_lock);
return retval;
}
static const char recursion_bug_msg [] =
KERN_CRIT "BUG: recent printk recursion!\n";
static int recursion_bug;
static int new_text_line = 1;
static char printk_buf[1024];
asmlinkage int vprintk(const char *fmt, va_list args)
{
int printed_len = 0;
int current_log_level = default_message_loglevel;
unsigned long flags;
int this_cpu;
char *p;
boot_delay_msec();
preempt_disable();
/* This stops the holder of console_sem just where we want him */
raw_local_irq_save(flags);
this_cpu = smp_processor_id();
/*
* Ouch, printk recursed into itself!
*/
if (unlikely(printk_cpu == this_cpu)) {
/*
* If a crash is occurring during printk() on this CPU,
* then try to get the crash message out but make sure
* we can't deadlock. Otherwise just return to avoid the
* recursion and return - but flag the recursion so that
* it can be printed at the next appropriate moment:
*/
if (!oops_in_progress) {
recursion_bug = 1;
goto out_restore_irqs;
}
zap_locks();
}
lockdep_off();
spin_lock(&logbuf_lock);
printk_cpu = this_cpu;
if (recursion_bug) {
recursion_bug = 0;
strcpy(printk_buf, recursion_bug_msg);
printed_len = strlen(recursion_bug_msg);
}
/* Emit the output into the temporary buffer */
printed_len += vscnprintf(printk_buf + printed_len,
sizeof(printk_buf) - printed_len, fmt, args);
/*
* Copy the output into log_buf. If the caller didn't provide
* appropriate log level tags, we insert them here
*/
for (p = printk_buf; *p; p++) {
if (new_text_line) {
/* If a token, set current_log_level and skip over */
if (p[0] == '<' && p[1] >= '0' && p[1] <= '7' &&
p[2] == '>') {
current_log_level = p[1] - '0';
p += 3;
printed_len -= 3;
}
/* Always output the token */
emit_log_char('<');
emit_log_char(current_log_level + '0');
emit_log_char('>');
printed_len += 3;
new_text_line = 0;
if (printk_time) {
/* Follow the token with the time */
char tbuf[50], *tp;
unsigned tlen;
unsigned long long t;
unsigned long nanosec_rem;
t = cpu_clock(printk_cpu);
nanosec_rem = do_div(t, 1000000000);
tlen = sprintf(tbuf, "[%5lu.%06lu] ",
(unsigned long) t,
nanosec_rem / 1000);
for (tp = tbuf; tp < tbuf + tlen; tp++)
emit_log_char(*tp);
printed_len += tlen;
}
if (!*p)
break;
}
emit_log_char(*p);
if (*p == '\n')
new_text_line = 1;
}
/*
* Try to acquire and then immediately release the
* console semaphore. The release will do all the
* actual magic (print out buffers, wake up klogd,
* etc).
*
* The acquire_console_semaphore_for_printk() function
* will release 'logbuf_lock' regardless of whether it
* actually gets the semaphore or not.
*/
if (acquire_console_semaphore_for_printk(this_cpu))
release_console_sem();
lockdep_on();
out_restore_irqs:
raw_local_irq_restore(flags);
preempt_enable();
return printed_len;
}
EXPORT_SYMBOL(printk);
EXPORT_SYMBOL(vprintk);
#else
static void call_console_drivers(unsigned start, unsigned end)
{
}
#endif
static int __add_preferred_console(char *name, int idx, char *options,
char *brl_options)
{
struct console_cmdline *c;
int i;
/*
* See if this tty is not yet registered, and
* if we have a slot free.
*/
for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
if (strcmp(console_cmdline[i].name, name) == 0 &&
console_cmdline[i].index == idx) {
if (!brl_options)
selected_console = i;
return 0;
}
if (i == MAX_CMDLINECONSOLES)
return -E2BIG;
if (!brl_options)
selected_console = i;
c = &console_cmdline[i];
strlcpy(c->name, name, sizeof(c->name));
c->options = options;
#ifdef CONFIG_A11Y_BRAILLE_CONSOLE
c->brl_options = brl_options;
#endif
c->index = idx;
return 0;
}
/*
* Set up a list of consoles. Called from init/main.c
*/
static int __init console_setup(char *str)
{
char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
char *s, *options, *brl_options = NULL;
int idx;
#ifdef CONFIG_A11Y_BRAILLE_CONSOLE
if (!memcmp(str, "brl,", 4)) {
brl_options = "";
str += 4;
} else if (!memcmp(str, "brl=", 4)) {
brl_options = str + 4;
str = strchr(brl_options, ',');
if (!str) {
printk(KERN_ERR "need port name after brl=\n");
return 1;
}
*(str++) = 0;
}
#endif
/*
* Decode str into name, index, options.
*/
if (str[0] >= '0' && str[0] <= '9') {
strcpy(buf, "ttyS");
strncpy(buf + 4, str, sizeof(buf) - 5);
} else {
strncpy(buf, str, sizeof(buf) - 1);
}
buf[sizeof(buf) - 1] = 0;
if ((options = strchr(str, ',')) != NULL)
*(options++) = 0;
#ifdef __sparc__
if (!strcmp(str, "ttya"))
strcpy(buf, "ttyS0");
if (!strcmp(str, "ttyb"))
strcpy(buf, "ttyS1");
#endif
for (s = buf; *s; s++)
if ((*s >= '0' && *s <= '9') || *s == ',')
break;
idx = simple_strtoul(s, NULL, 10);
*s = 0;
__add_preferred_console(buf, idx, options, brl_options);
console_set_on_cmdline = 1;
return 1;
}
__setup("console=", console_setup);
/**
* add_preferred_console - add a device to the list of preferred consoles.
* @name: device name
* @idx: device index
* @options: options for this console
*
* The last preferred console added will be used for kernel messages
* and stdin/out/err for init. Normally this is used by console_setup
* above to handle user-supplied console arguments; however it can also
* be used by arch-specific code either to override the user or more
* commonly to provide a default console (ie from PROM variables) when
* the user has not supplied one.
*/
int add_preferred_console(char *name, int idx, char *options)
{
return __add_preferred_console(name, idx, options, NULL);
}
int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
{
struct console_cmdline *c;
int i;
for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
if (strcmp(console_cmdline[i].name, name) == 0 &&
console_cmdline[i].index == idx) {
c = &console_cmdline[i];
strlcpy(c->name, name_new, sizeof(c->name));
c->name[sizeof(c->name) - 1] = 0;
c->options = options;
c->index = idx_new;
return i;
}
/* not found */
return -1;
}
int console_suspend_enabled = 1;
EXPORT_SYMBOL(console_suspend_enabled);
static int __init console_suspend_disable(char *str)
{
console_suspend_enabled = 0;
return 1;
}
__setup("no_console_suspend", console_suspend_disable);
/**
* suspend_console - suspend the console subsystem
*
* This disables printk() while we go into suspend states
*/
void suspend_console(void)
{
if (!console_suspend_enabled)
return;
printk("Suspending console(s) (use no_console_suspend to debug)\n");
acquire_console_sem();
console_suspended = 1;
up(&console_sem);
}
void resume_console(void)
{
if (!console_suspend_enabled)
return;
down(&console_sem);
console_suspended = 0;
release_console_sem();
}
/**
* acquire_console_sem - lock the console system for exclusive use.
*
* Acquires a semaphore which guarantees that the caller has
* exclusive access to the console system and the console_drivers list.
*
* Can sleep, returns nothing.
*/
void acquire_console_sem(void)
{
BUG_ON(in_interrupt());
down(&console_sem);
if (console_suspended)
return;
console_locked = 1;
console_may_schedule = 1;
}
EXPORT_SYMBOL(acquire_console_sem);
int try_acquire_console_sem(void)
{
if (down_trylock(&console_sem))
return -1;
if (console_suspended) {
up(&console_sem);
return -1;
}
console_locked = 1;
console_may_schedule = 0;
return 0;
}
EXPORT_SYMBOL(try_acquire_console_sem);
int is_console_locked(void)
{
return console_locked;
}
static DEFINE_PER_CPU(int, printk_pending);
void printk_tick(void)
{
if (__get_cpu_var(printk_pending)) {
__get_cpu_var(printk_pending) = 0;
wake_up_interruptible(&log_wait);
}
}
int printk_needs_cpu(int cpu)
{
return per_cpu(printk_pending, cpu);
}
void wake_up_klogd(void)
{
if (waitqueue_active(&log_wait))
__raw_get_cpu_var(printk_pending) = 1;
}
/**
* release_console_sem - unlock the console system
*
* Releases the semaphore which the caller holds on the console system
* and the console driver list.
*
* While the semaphore was held, console output may have been buffered
* by printk(). If this is the case, release_console_sem() emits
* the output prior to releasing the semaphore.
*
* If there is output waiting for klogd, we wake it up.
*
* release_console_sem() may be called from any context.
*/
void release_console_sem(void)
{
unsigned long flags;
unsigned _con_start, _log_end;
unsigned wake_klogd = 0;
if (console_suspended) {
up(&console_sem);
return;
}
console_may_schedule = 0;
for ( ; ; ) {
spin_lock_irqsave(&logbuf_lock, flags);
wake_klogd |= log_start - log_end;
if (con_start == log_end)
break; /* Nothing to print */
_con_start = con_start;
_log_end = log_end;
con_start = log_end; /* Flush */
spin_unlock(&logbuf_lock);
stop_critical_timings(); /* don't trace print latency */
call_console_drivers(_con_start, _log_end);
start_critical_timings();
local_irq_restore(flags);
}
console_locked = 0;
up(&console_sem);
spin_unlock_irqrestore(&logbuf_lock, flags);
if (wake_klogd)
wake_up_klogd();
}
EXPORT_SYMBOL(release_console_sem);
/**
* console_conditional_schedule - yield the CPU if required
*
* If the console code is currently allowed to sleep, and
* if this CPU should yield the CPU to another task, do
* so here.
*
* Must be called within acquire_console_sem().
*/
void __sched console_conditional_schedule(void)
{
if (console_may_schedule)
cond_resched();
}
EXPORT_SYMBOL(console_conditional_schedule);
void console_print(const char *s)
{
printk(KERN_EMERG "%s", s);
}
EXPORT_SYMBOL(console_print);
void console_unblank(void)
{
struct console *c;
/*
* console_unblank can no longer be called in interrupt context unless
* oops_in_progress is set to 1..
*/
if (oops_in_progress) {
if (down_trylock(&console_sem) != 0)
return;
} else
acquire_console_sem();
console_locked = 1;
console_may_schedule = 0;
for (c = console_drivers; c != NULL; c = c->next)
if ((c->flags & CON_ENABLED) && c->unblank)
c->unblank();
release_console_sem();
}
/*
* Return the console tty driver structure and its associated index
*/
struct tty_driver *console_device(int *index)
{
struct console *c;
struct tty_driver *driver = NULL;
acquire_console_sem();
for (c = console_drivers; c != NULL; c = c->next) {
if (!c->device)
continue;
driver = c->device(c, index);
if (driver)
break;
}
release_console_sem();
return driver;
}
/*
* Prevent further output on the passed console device so that (for example)
* serial drivers can disable console output before suspending a port, and can
* re-enable output afterwards.
*/
void console_stop(struct console *console)
{
acquire_console_sem();
console->flags &= ~CON_ENABLED;
release_console_sem();
}
EXPORT_SYMBOL(console_stop);
void console_start(struct console *console)
{
acquire_console_sem();
console->flags |= CON_ENABLED;
release_console_sem();
}
EXPORT_SYMBOL(console_start);
/*
* The console driver calls this routine during kernel initialization
* to register the console printing procedure with printk() and to
* print any messages that were printed by the kernel before the
* console driver was initialized.
*/
void register_console(struct console *console)
{
int i;
unsigned long flags;
struct console *bootconsole = NULL;
if (console_drivers) {
if (console->flags & CON_BOOT)
return;
if (console_drivers->flags & CON_BOOT)
bootconsole = console_drivers;
}
if (preferred_console < 0 || bootconsole || !console_drivers)
preferred_console = selected_console;
if (console->early_setup)
console->early_setup();
/*
* See if we want to use this console driver. If we
* didn't select a console we take the first one
* that registers here.
*/
if (preferred_console < 0) {
if (console->index < 0)
console->index = 0;
if (console->setup == NULL ||
console->setup(console, NULL) == 0) {
console->flags |= CON_ENABLED;
if (console->device) {
console->flags |= CON_CONSDEV;
preferred_console = 0;
}
}
}
/*
* See if this console matches one we selected on
* the command line.
*/
for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
i++) {
if (strcmp(console_cmdline[i].name, console->name) != 0)
continue;
if (console->index >= 0 &&
console->index != console_cmdline[i].index)
continue;
if (console->index < 0)
console->index = console_cmdline[i].index;
#ifdef CONFIG_A11Y_BRAILLE_CONSOLE
if (console_cmdline[i].brl_options) {
console->flags |= CON_BRL;
braille_register_console(console,
console_cmdline[i].index,
console_cmdline[i].options,
console_cmdline[i].brl_options);
return;
}
#endif
if (console->setup &&
console->setup(console, console_cmdline[i].options) != 0)
break;
console->flags |= CON_ENABLED;
console->index = console_cmdline[i].index;
if (i == selected_console) {
console->flags |= CON_CONSDEV;
preferred_console = selected_console;
}
break;
}
if (!(console->flags & CON_ENABLED))
return;
if (bootconsole && (console->flags & CON_CONSDEV)) {
printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
bootconsole->name, bootconsole->index,
console->name, console->index);
unregister_console(bootconsole);
console->flags &= ~CON_PRINTBUFFER;
} else {
printk(KERN_INFO "console [%s%d] enabled\n",
console->name, console->index);
}
/*
* Put this console in the list - keep the
* preferred driver at the head of the list.
*/
acquire_console_sem();
if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
console->next = console_drivers;
console_drivers = console;
if (console->next)
console->next->flags &= ~CON_CONSDEV;
} else {
console->next = console_drivers->next;
console_drivers->next = console;
}
if (console->flags & CON_PRINTBUFFER) {
/*
* release_console_sem() will print out the buffered messages
* for us.
*/
spin_lock_irqsave(&logbuf_lock, flags);
con_start = log_start;
spin_unlock_irqrestore(&logbuf_lock, flags);
}
release_console_sem();
}
EXPORT_SYMBOL(register_console);
int unregister_console(struct console *console)
{
struct console *a, *b;
int res = 1;
#ifdef CONFIG_A11Y_BRAILLE_CONSOLE
if (console->flags & CON_BRL)
return braille_unregister_console(console);
#endif
acquire_console_sem();
if (console_drivers == console) {
console_drivers=console->next;
res = 0;
} else if (console_drivers) {
for (a=console_drivers->next, b=console_drivers ;
a; b=a, a=b->next) {
if (a == console) {
b->next = a->next;
res = 0;
break;
}
}
}
/*
* If this isn't the last console and it has CON_CONSDEV set, we
* need to set it on the next preferred console.
*/
if (console_drivers != NULL && console->flags & CON_CONSDEV)
console_drivers->flags |= CON_CONSDEV;
release_console_sem();
return res;
}
EXPORT_SYMBOL(unregister_console);
static int __init disable_boot_consoles(void)
{
if (console_drivers != NULL) {
if (console_drivers->flags & CON_BOOT) {
printk(KERN_INFO "turn off boot console %s%d\n",
console_drivers->name, console_drivers->index);
return unregister_console(console_drivers);
}
}
return 0;
}
late_initcall(disable_boot_consoles);
#if defined CONFIG_PRINTK
/*
* printk rate limiting, lifted from the networking subsystem.
*
* This enforces a rate limit: not more than 10 kernel messages
* every 5s to make a denial-of-service attack impossible.
*/
DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
int printk_ratelimit(void)
{
return __ratelimit(&printk_ratelimit_state);
}
EXPORT_SYMBOL(printk_ratelimit);
/**
* printk_timed_ratelimit - caller-controlled printk ratelimiting
* @caller_jiffies: pointer to caller's state
* @interval_msecs: minimum interval between prints
*
* printk_timed_ratelimit() returns true if more than @interval_msecs
* milliseconds have elapsed since the last time printk_timed_ratelimit()
* returned true.
*/
bool printk_timed_ratelimit(unsigned long *caller_jiffies,
unsigned int interval_msecs)
{
if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
*caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
return true;
}
return false;
}
EXPORT_SYMBOL(printk_timed_ratelimit);
#endif