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linux / linux / kernel / git / bpf / bpf / fc16a5322ee6c30ea848818722eee5d352f8d127 / . / kernel / printk / printk.c
blob: 142a58d124d95ae9b1e07e360903f02f7c5d8c28 [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0-only
/*
* 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
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#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/delay.h>
#include <linux/smp.h>
#include <linux/security.h>
#include <linux/memblock.h>
#include <linux/syscalls.h>
#include <linux/crash_core.h>
#include <linux/ratelimit.h>
#include <linux/kmsg_dump.h>
#include <linux/syslog.h>
#include <linux/cpu.h>
#include <linux/rculist.h>
#include <linux/poll.h>
#include <linux/irq_work.h>
#include <linux/ctype.h>
#include <linux/uio.h>
#include <linux/sched/clock.h>
#include <linux/sched/debug.h>
#include <linux/sched/task_stack.h>
#include <linux/uaccess.h>
#include <asm/sections.h>
#include <trace/events/initcall.h>
#define CREATE_TRACE_POINTS
#include <trace/events/printk.h>
#include "printk_ringbuffer.h"
#include "console_cmdline.h"
#include "braille.h"
#include "internal.h"
int console_printk[4] = {
CONSOLE_LOGLEVEL_DEFAULT, /* console_loglevel */
MESSAGE_LOGLEVEL_DEFAULT, /* default_message_loglevel */
CONSOLE_LOGLEVEL_MIN, /* minimum_console_loglevel */
CONSOLE_LOGLEVEL_DEFAULT, /* default_console_loglevel */
};
EXPORT_SYMBOL_GPL(console_printk);
atomic_t ignore_console_lock_warning __read_mostly = ATOMIC_INIT(0);
EXPORT_SYMBOL(ignore_console_lock_warning);
/*
* 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);
/*
* System may need to suppress printk message under certain
* circumstances, like after kernel panic happens.
*/
int __read_mostly suppress_printk;
#ifdef CONFIG_LOCKDEP
static struct lockdep_map console_lock_dep_map = {
.name = "console_lock"
};
#endif
enum devkmsg_log_bits {
__DEVKMSG_LOG_BIT_ON = 0,
__DEVKMSG_LOG_BIT_OFF,
__DEVKMSG_LOG_BIT_LOCK,
};
enum devkmsg_log_masks {
DEVKMSG_LOG_MASK_ON = BIT(__DEVKMSG_LOG_BIT_ON),
DEVKMSG_LOG_MASK_OFF = BIT(__DEVKMSG_LOG_BIT_OFF),
DEVKMSG_LOG_MASK_LOCK = BIT(__DEVKMSG_LOG_BIT_LOCK),
};
/* Keep both the 'on' and 'off' bits clear, i.e. ratelimit by default: */
#define DEVKMSG_LOG_MASK_DEFAULT 0
static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
static int __control_devkmsg(char *str)
{
size_t len;
if (!str)
return -EINVAL;
len = str_has_prefix(str, "on");
if (len) {
devkmsg_log = DEVKMSG_LOG_MASK_ON;
return len;
}
len = str_has_prefix(str, "off");
if (len) {
devkmsg_log = DEVKMSG_LOG_MASK_OFF;
return len;
}
len = str_has_prefix(str, "ratelimit");
if (len) {
devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
return len;
}
return -EINVAL;
}
static int __init control_devkmsg(char *str)
{
if (__control_devkmsg(str) < 0)
return 1;
/*
* Set sysctl string accordingly:
*/
if (devkmsg_log == DEVKMSG_LOG_MASK_ON)
strcpy(devkmsg_log_str, "on");
else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF)
strcpy(devkmsg_log_str, "off");
/* else "ratelimit" which is set by default. */
/*
* Sysctl cannot change it anymore. The kernel command line setting of
* this parameter is to force the setting to be permanent throughout the
* runtime of the system. This is a precation measure against userspace
* trying to be a smarta** and attempting to change it up on us.
*/
devkmsg_log |= DEVKMSG_LOG_MASK_LOCK;
return 0;
}
__setup("printk.devkmsg=", control_devkmsg);
char devkmsg_log_str[DEVKMSG_STR_MAX_SIZE] = "ratelimit";
int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write,
void *buffer, size_t *lenp, loff_t *ppos)
{
char old_str[DEVKMSG_STR_MAX_SIZE];
unsigned int old;
int err;
if (write) {
if (devkmsg_log & DEVKMSG_LOG_MASK_LOCK)
return -EINVAL;
old = devkmsg_log;
strncpy(old_str, devkmsg_log_str, DEVKMSG_STR_MAX_SIZE);
}
err = proc_dostring(table, write, buffer, lenp, ppos);
if (err)
return err;
if (write) {
err = __control_devkmsg(devkmsg_log_str);
/*
* Do not accept an unknown string OR a known string with
* trailing crap...
*/
if (err < 0 || (err + 1 != *lenp)) {
/* ... and restore old setting. */
devkmsg_log = old;
strncpy(devkmsg_log_str, old_str, DEVKMSG_STR_MAX_SIZE);
return -EINVAL;
}
}
return 0;
}
/* Number of registered extended console drivers. */
static int nr_ext_console_drivers;
/*
* Helper macros to handle lockdep when locking/unlocking console_sem. We use
* macros instead of functions so that _RET_IP_ contains useful information.
*/
#define down_console_sem() do { \
down(&console_sem);\
mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);\
} while (0)
static int __down_trylock_console_sem(unsigned long ip)
{
int lock_failed;
unsigned long flags;
/*
* Here and in __up_console_sem() we need to be in safe mode,
* because spindump/WARN/etc from under console ->lock will
* deadlock in printk()->down_trylock_console_sem() otherwise.
*/
printk_safe_enter_irqsave(flags);
lock_failed = down_trylock(&console_sem);
printk_safe_exit_irqrestore(flags);
if (lock_failed)
return 1;
mutex_acquire(&console_lock_dep_map, 0, 1, ip);
return 0;
}
#define down_trylock_console_sem() __down_trylock_console_sem(_RET_IP_)
static void __up_console_sem(unsigned long ip)
{
unsigned long flags;
mutex_release(&console_lock_dep_map, ip);
printk_safe_enter_irqsave(flags);
up(&console_sem);
printk_safe_exit_irqrestore(flags);
}
#define up_console_sem() __up_console_sem(_RET_IP_)
/*
* 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 and are racing, but it helps tracking those weird code
* paths in the console code where we end up in places I want
* locked without the console semaphore held).
*/
static int console_locked, console_suspended;
/*
* 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=)
*/
#define MAX_CMDLINECONSOLES 8
static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
static int preferred_console = -1;
static bool has_preferred_console;
int console_set_on_cmdline;
EXPORT_SYMBOL(console_set_on_cmdline);
/* Flag: console code may call schedule() */
static int console_may_schedule;
enum con_msg_format_flags {
MSG_FORMAT_DEFAULT = 0,
MSG_FORMAT_SYSLOG = (1 << 0),
};
static int console_msg_format = MSG_FORMAT_DEFAULT;
/*
* The printk log buffer consists of a sequenced collection of records, each
* containing variable length message text. Every record also contains its
* own meta-data (@info).
*
* Every record meta-data carries the timestamp in microseconds, as well as
* the standard userspace syslog level and syslog facility. The usual kernel
* messages use LOG_KERN; userspace-injected messages always carry a matching
* syslog facility, by default LOG_USER. The origin of every message can be
* reliably determined that way.
*
* The human readable log message of a record is available in @text, the
* length of the message text in @text_len. The stored message is not
* terminated.
*
* Optionally, a record can carry a dictionary of properties (key/value
* pairs), to provide userspace with a machine-readable message context.
*
* Examples for well-defined, commonly used property names are:
* DEVICE=b12:8 device identifier
* b12:8 block dev_t
* c127:3 char dev_t
* n8 netdev ifindex
* +sound:card0 subsystem:devname
* SUBSYSTEM=pci driver-core subsystem name
*
* Valid characters in property names are [a-zA-Z0-9.-_]. Property names
* and values are terminated by a '\0' character.
*
* Example of record values:
* record.text_buf = "it's a line" (unterminated)
* record.info.seq = 56
* record.info.ts_nsec = 36863
* record.info.text_len = 11
* record.info.facility = 0 (LOG_KERN)
* record.info.flags = 0
* record.info.level = 3 (LOG_ERR)
* record.info.caller_id = 299 (task 299)
* record.info.dev_info.subsystem = "pci" (terminated)
* record.info.dev_info.device = "+pci:0000:00:01.0" (terminated)
*
* The 'struct printk_info' buffer must never be directly exported to
* userspace, it is a kernel-private implementation detail that might
* need to be changed in the future, when the requirements change.
*
* /dev/kmsg exports the structured data in the following line format:
* "<level>,<sequnum>,<timestamp>,<contflag>[,additional_values, ... ];<message text>\n"
*
* Users of the export format should ignore possible additional values
* separated by ',', and find the message after the ';' character.
*
* The optional key/value pairs are attached as continuation lines starting
* with a space character and terminated by a newline. All possible
* non-prinatable characters are escaped in the "\xff" notation.
*/
enum log_flags {
LOG_NEWLINE = 2, /* text ended with a newline */
LOG_CONT = 8, /* text is a fragment of a continuation line */
};
/* syslog_lock protects syslog_* variables and write access to clear_seq. */
static DEFINE_RAW_SPINLOCK(syslog_lock);
#ifdef CONFIG_PRINTK
DECLARE_WAIT_QUEUE_HEAD(log_wait);
/* All 3 protected by @syslog_lock. */
/* the next printk record to read by syslog(READ) or /proc/kmsg */
static u64 syslog_seq;
static size_t syslog_partial;
static bool syslog_time;
/* All 3 protected by @console_sem. */
/* the next printk record to write to the console */
static u64 console_seq;
static u64 exclusive_console_stop_seq;
static unsigned long console_dropped;
struct latched_seq {
seqcount_latch_t latch;
u64 val[2];
};
/*
* The next printk record to read after the last 'clear' command. There are
* two copies (updated with seqcount_latch) so that reads can locklessly
* access a valid value. Writers are synchronized by @syslog_lock.
*/
static struct latched_seq clear_seq = {
.latch = SEQCNT_LATCH_ZERO(clear_seq.latch),
.val[0] = 0,
.val[1] = 0,
};
#ifdef CONFIG_PRINTK_CALLER
#define PREFIX_MAX 48
#else
#define PREFIX_MAX 32
#endif
/* the maximum size of a formatted record (i.e. with prefix added per line) */
#define CONSOLE_LOG_MAX 1024
/* the maximum size allowed to be reserved for a record */
#define LOG_LINE_MAX (CONSOLE_LOG_MAX - PREFIX_MAX)
#define LOG_LEVEL(v) ((v) & 0x07)
#define LOG_FACILITY(v) ((v) >> 3 & 0xff)
/* record buffer */
#define LOG_ALIGN __alignof__(unsigned long)
#define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
#define LOG_BUF_LEN_MAX (u32)(1 << 31)
static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
static char *log_buf = __log_buf;
static u32 log_buf_len = __LOG_BUF_LEN;
/*
* Define the average message size. This only affects the number of
* descriptors that will be available. Underestimating is better than
* overestimating (too many available descriptors is better than not enough).
*/
#define PRB_AVGBITS 5 /* 32 character average length */
#if CONFIG_LOG_BUF_SHIFT <= PRB_AVGBITS
#error CONFIG_LOG_BUF_SHIFT value too small.
#endif
_DEFINE_PRINTKRB(printk_rb_static, CONFIG_LOG_BUF_SHIFT - PRB_AVGBITS,
PRB_AVGBITS, &__log_buf[0]);
static struct printk_ringbuffer printk_rb_dynamic;
static struct printk_ringbuffer *prb = &printk_rb_static;
/*
* We cannot access per-CPU data (e.g. per-CPU flush irq_work) before
* per_cpu_areas are initialised. This variable is set to true when
* it's safe to access per-CPU data.
*/
static bool __printk_percpu_data_ready __read_mostly;
bool printk_percpu_data_ready(void)
{
return __printk_percpu_data_ready;
}
/* Must be called under syslog_lock. */
static void latched_seq_write(struct latched_seq *ls, u64 val)
{
raw_write_seqcount_latch(&ls->latch);
ls->val[0] = val;
raw_write_seqcount_latch(&ls->latch);
ls->val[1] = val;
}
/* Can be called from any context. */
static u64 latched_seq_read_nolock(struct latched_seq *ls)
{
unsigned int seq;
unsigned int idx;
u64 val;
do {
seq = raw_read_seqcount_latch(&ls->latch);
idx = seq & 0x1;
val = ls->val[idx];
} while (read_seqcount_latch_retry(&ls->latch, seq));
return val;
}
/* Return log buffer address */
char *log_buf_addr_get(void)
{
return log_buf;
}
/* Return log buffer size */
u32 log_buf_len_get(void)
{
return log_buf_len;
}
/*
* Define how much of the log buffer we could take at maximum. The value
* must be greater than two. Note that only half of the buffer is available
* when the index points to the middle.
*/
#define MAX_LOG_TAKE_PART 4
static const char trunc_msg[] = "<truncated>";
static void truncate_msg(u16 *text_len, u16 *trunc_msg_len)
{
/*
* The message should not take the whole buffer. Otherwise, it might
* get removed too soon.
*/
u32 max_text_len = log_buf_len / MAX_LOG_TAKE_PART;
if (*text_len > max_text_len)
*text_len = max_text_len;
/* enable the warning message (if there is room) */
*trunc_msg_len = strlen(trunc_msg);
if (*text_len >= *trunc_msg_len)
*text_len -= *trunc_msg_len;
else
*trunc_msg_len = 0;
}
int dmesg_restrict = IS_ENABLED(CONFIG_SECURITY_DMESG_RESTRICT);
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, int source)
{
/*
* If this is from /proc/kmsg and we've already opened it, then we've
* already done the capabilities checks at open time.
*/
if (source == SYSLOG_FROM_PROC && type != SYSLOG_ACTION_OPEN)
goto ok;
if (syslog_action_restricted(type)) {
if (capable(CAP_SYSLOG))
goto ok;
/*
* For historical reasons, accept CAP_SYS_ADMIN too, with
* a warning.
*/
if (capable(CAP_SYS_ADMIN)) {
pr_warn_once("%s (%d): Attempt to access syslog with "
"CAP_SYS_ADMIN but no CAP_SYSLOG "
"(deprecated).\n",
current->comm, task_pid_nr(current));
goto ok;
}
return -EPERM;
}
ok:
return security_syslog(type);
}
static void append_char(char **pp, char *e, char c)
{
if (*pp < e)
*(*pp)++ = c;
}
static ssize_t info_print_ext_header(char *buf, size_t size,
struct printk_info *info)
{
u64 ts_usec = info->ts_nsec;
char caller[20];
#ifdef CONFIG_PRINTK_CALLER
u32 id = info->caller_id;
snprintf(caller, sizeof(caller), ",caller=%c%u",
id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
#else
caller[0] = '\0';
#endif
do_div(ts_usec, 1000);
return scnprintf(buf, size, "%u,%llu,%llu,%c%s;",
(info->facility << 3) | info->level, info->seq,
ts_usec, info->flags & LOG_CONT ? 'c' : '-', caller);
}
static ssize_t msg_add_ext_text(char *buf, size_t size,
const char *text, size_t text_len,
unsigned char endc)
{
char *p = buf, *e = buf + size;
size_t i;
/* escape non-printable characters */
for (i = 0; i < text_len; i++) {
unsigned char c = text[i];
if (c < ' ' || c >= 127 || c == '\\')
p += scnprintf(p, e - p, "\\x%02x", c);
else
append_char(&p, e, c);
}
append_char(&p, e, endc);
return p - buf;
}
static ssize_t msg_add_dict_text(char *buf, size_t size,
const char *key, const char *val)
{
size_t val_len = strlen(val);
ssize_t len;
if (!val_len)
return 0;
len = msg_add_ext_text(buf, size, "", 0, ' '); /* dict prefix */
len += msg_add_ext_text(buf + len, size - len, key, strlen(key), '=');
len += msg_add_ext_text(buf + len, size - len, val, val_len, '\n');
return len;
}
static ssize_t msg_print_ext_body(char *buf, size_t size,
char *text, size_t text_len,
struct dev_printk_info *dev_info)
{
ssize_t len;
len = msg_add_ext_text(buf, size, text, text_len, '\n');
if (!dev_info)
goto out;
len += msg_add_dict_text(buf + len, size - len, "SUBSYSTEM",
dev_info->subsystem);
len += msg_add_dict_text(buf + len, size - len, "DEVICE",
dev_info->device);
out:
return len;
}
/* /dev/kmsg - userspace message inject/listen interface */
struct devkmsg_user {
atomic64_t seq;
struct ratelimit_state rs;
struct mutex lock;
char buf[CONSOLE_EXT_LOG_MAX];
struct printk_info info;
char text_buf[CONSOLE_EXT_LOG_MAX];
struct printk_record record;
};
static __printf(3, 4) __cold
int devkmsg_emit(int facility, int level, const char *fmt, ...)
{
va_list args;
int r;
va_start(args, fmt);
r = vprintk_emit(facility, level, NULL, fmt, args);
va_end(args);
return r;
}
static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
{
char *buf, *line;
int level = default_message_loglevel;
int facility = 1; /* LOG_USER */
struct file *file = iocb->ki_filp;
struct devkmsg_user *user = file->private_data;
size_t len = iov_iter_count(from);
ssize_t ret = len;
if (!user || len > LOG_LINE_MAX)
return -EINVAL;
/* Ignore when user logging is disabled. */
if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
return len;
/* Ratelimit when not explicitly enabled. */
if (!(devkmsg_log & DEVKMSG_LOG_MASK_ON)) {
if (!___ratelimit(&user->rs, current->comm))
return ret;
}
buf = kmalloc(len+1, GFP_KERNEL);
if (buf == NULL)
return -ENOMEM;
buf[len] = '\0';
if (!copy_from_iter_full(buf, len, from)) {
kfree(buf);
return -EFAULT;
}
/*
* Extract and skip the syslog prefix <[0-9]*>. Coming from userspace
* the decimal value represents 32bit, the lower 3 bit are the log
* level, the rest are the log facility.
*
* If no prefix or no userspace facility is specified, we
* enforce LOG_USER, to be able to reliably distinguish
* kernel-generated messages from userspace-injected ones.
*/
line = buf;
if (line[0] == '<') {
char *endp = NULL;
unsigned int u;
u = simple_strtoul(line + 1, &endp, 10);
if (endp && endp[0] == '>') {
level = LOG_LEVEL(u);
if (LOG_FACILITY(u) != 0)
facility = LOG_FACILITY(u);
endp++;
line = endp;
}
}
devkmsg_emit(facility, level, "%s", line);
kfree(buf);
return ret;
}
static ssize_t devkmsg_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
struct devkmsg_user *user = file->private_data;
struct printk_record *r = &user->record;
size_t len;
ssize_t ret;
if (!user)
return -EBADF;
ret = mutex_lock_interruptible(&user->lock);
if (ret)
return ret;
printk_safe_enter_irq();
if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
if (file->f_flags & O_NONBLOCK) {
ret = -EAGAIN;
printk_safe_exit_irq();
goto out;
}
printk_safe_exit_irq();
ret = wait_event_interruptible(log_wait,
prb_read_valid(prb, atomic64_read(&user->seq), r));
if (ret)
goto out;
printk_safe_enter_irq();
}
if (r->info->seq != atomic64_read(&user->seq)) {
/* our last seen message is gone, return error and reset */
atomic64_set(&user->seq, r->info->seq);
ret = -EPIPE;
printk_safe_exit_irq();
goto out;
}
len = info_print_ext_header(user->buf, sizeof(user->buf), r->info);
len += msg_print_ext_body(user->buf + len, sizeof(user->buf) - len,
&r->text_buf[0], r->info->text_len,
&r->info->dev_info);
atomic64_set(&user->seq, r->info->seq + 1);
printk_safe_exit_irq();
if (len > count) {
ret = -EINVAL;
goto out;
}
if (copy_to_user(buf, user->buf, len)) {
ret = -EFAULT;
goto out;
}
ret = len;
out:
mutex_unlock(&user->lock);
return ret;
}
/*
* Be careful when modifying this function!!!
*
* Only few operations are supported because the device works only with the
* entire variable length messages (records). Non-standard values are
* returned in the other cases and has been this way for quite some time.
* User space applications might depend on this behavior.
*/
static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
{
struct devkmsg_user *user = file->private_data;
loff_t ret = 0;
if (!user)
return -EBADF;
if (offset)
return -ESPIPE;
printk_safe_enter_irq();
switch (whence) {
case SEEK_SET:
/* the first record */
atomic64_set(&user->seq, prb_first_valid_seq(prb));
break;
case SEEK_DATA:
/*
* The first record after the last SYSLOG_ACTION_CLEAR,
* like issued by 'dmesg -c'. Reading /dev/kmsg itself
* changes no global state, and does not clear anything.
*/
atomic64_set(&user->seq, latched_seq_read_nolock(&clear_seq));
break;
case SEEK_END:
/* after the last record */
atomic64_set(&user->seq, prb_next_seq(prb));
break;
default:
ret = -EINVAL;
}
printk_safe_exit_irq();
return ret;
}
static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
{
struct devkmsg_user *user = file->private_data;
struct printk_info info;
__poll_t ret = 0;
if (!user)
return EPOLLERR|EPOLLNVAL;
poll_wait(file, &log_wait, wait);
printk_safe_enter_irq();
if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {
/* return error when data has vanished underneath us */
if (info.seq != atomic64_read(&user->seq))
ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
else
ret = EPOLLIN|EPOLLRDNORM;
}
printk_safe_exit_irq();
return ret;
}
static int devkmsg_open(struct inode *inode, struct file *file)
{
struct devkmsg_user *user;
int err;
if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
return -EPERM;
/* write-only does not need any file context */
if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
SYSLOG_FROM_READER);
if (err)
return err;
}
user = kmalloc(sizeof(struct devkmsg_user), GFP_KERNEL);
if (!user)
return -ENOMEM;
ratelimit_default_init(&user->rs);
ratelimit_set_flags(&user->rs, RATELIMIT_MSG_ON_RELEASE);
mutex_init(&user->lock);
prb_rec_init_rd(&user->record, &user->info,
&user->text_buf[0], sizeof(user->text_buf));
printk_safe_enter_irq();
atomic64_set(&user->seq, prb_first_valid_seq(prb));
printk_safe_exit_irq();
file->private_data = user;
return 0;
}
static int devkmsg_release(struct inode *inode, struct file *file)
{
struct devkmsg_user *user = file->private_data;
if (!user)
return 0;
ratelimit_state_exit(&user->rs);
mutex_destroy(&user->lock);
kfree(user);
return 0;
}
const struct file_operations kmsg_fops = {
.open = devkmsg_open,
.read = devkmsg_read,
.write_iter = devkmsg_write,
.llseek = devkmsg_llseek,
.poll = devkmsg_poll,
.release = devkmsg_release,
};
#ifdef CONFIG_CRASH_CORE
/*
* This appends the listed symbols to /proc/vmcore
*
* /proc/vmcore is used by various utilities, 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_vmcoreinfo_setup(void)
{
struct dev_printk_info *dev_info = NULL;
VMCOREINFO_SYMBOL(prb);
VMCOREINFO_SYMBOL(printk_rb_static);
VMCOREINFO_SYMBOL(clear_seq);
/*
* Export struct size and field offsets. User space tools can
* parse it and detect any changes to structure down the line.
*/
VMCOREINFO_STRUCT_SIZE(printk_ringbuffer);
VMCOREINFO_OFFSET(printk_ringbuffer, desc_ring);
VMCOREINFO_OFFSET(printk_ringbuffer, text_data_ring);
VMCOREINFO_OFFSET(printk_ringbuffer, fail);
VMCOREINFO_STRUCT_SIZE(prb_desc_ring);
VMCOREINFO_OFFSET(prb_desc_ring, count_bits);
VMCOREINFO_OFFSET(prb_desc_ring, descs);
VMCOREINFO_OFFSET(prb_desc_ring, infos);
VMCOREINFO_OFFSET(prb_desc_ring, head_id);
VMCOREINFO_OFFSET(prb_desc_ring, tail_id);
VMCOREINFO_STRUCT_SIZE(prb_desc);
VMCOREINFO_OFFSET(prb_desc, state_var);
VMCOREINFO_OFFSET(prb_desc, text_blk_lpos);
VMCOREINFO_STRUCT_SIZE(prb_data_blk_lpos);
VMCOREINFO_OFFSET(prb_data_blk_lpos, begin);
VMCOREINFO_OFFSET(prb_data_blk_lpos, next);
VMCOREINFO_STRUCT_SIZE(printk_info);
VMCOREINFO_OFFSET(printk_info, seq);
VMCOREINFO_OFFSET(printk_info, ts_nsec);
VMCOREINFO_OFFSET(printk_info, text_len);
VMCOREINFO_OFFSET(printk_info, caller_id);
VMCOREINFO_OFFSET(printk_info, dev_info);
VMCOREINFO_STRUCT_SIZE(dev_printk_info);
VMCOREINFO_OFFSET(dev_printk_info, subsystem);
VMCOREINFO_LENGTH(printk_info_subsystem, sizeof(dev_info->subsystem));
VMCOREINFO_OFFSET(dev_printk_info, device);
VMCOREINFO_LENGTH(printk_info_device, sizeof(dev_info->device));
VMCOREINFO_STRUCT_SIZE(prb_data_ring);
VMCOREINFO_OFFSET(prb_data_ring, size_bits);
VMCOREINFO_OFFSET(prb_data_ring, data);
VMCOREINFO_OFFSET(prb_data_ring, head_lpos);
VMCOREINFO_OFFSET(prb_data_ring, tail_lpos);
VMCOREINFO_SIZE(atomic_long_t);
VMCOREINFO_TYPE_OFFSET(atomic_long_t, counter);
VMCOREINFO_STRUCT_SIZE(latched_seq);
VMCOREINFO_OFFSET(latched_seq, val);
}
#endif
/* requested log_buf_len from kernel cmdline */
static unsigned long __initdata new_log_buf_len;
/* we practice scaling the ring buffer by powers of 2 */
static void __init log_buf_len_update(u64 size)
{
if (size > (u64)LOG_BUF_LEN_MAX) {
size = (u64)LOG_BUF_LEN_MAX;
pr_err("log_buf over 2G is not supported.\n");
}
if (size)
size = roundup_pow_of_two(size);
if (size > log_buf_len)
new_log_buf_len = (unsigned long)size;
}
/* save requested log_buf_len since it's too early to process it */
static int __init log_buf_len_setup(char *str)
{
u64 size;
if (!str)
return -EINVAL;
size = memparse(str, &str);
log_buf_len_update(size);
return 0;
}
early_param("log_buf_len", log_buf_len_setup);
#ifdef CONFIG_SMP
#define __LOG_CPU_MAX_BUF_LEN (1 << CONFIG_LOG_CPU_MAX_BUF_SHIFT)
static void __init log_buf_add_cpu(void)
{
unsigned int cpu_extra;
/*
* archs should set up cpu_possible_bits properly with
* set_cpu_possible() after setup_arch() but just in
* case lets ensure this is valid.
*/
if (num_possible_cpus() == 1)
return;
cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN;
/* by default this will only continue through for large > 64 CPUs */
if (cpu_extra <= __LOG_BUF_LEN / 2)
return;
pr_info("log_buf_len individual max cpu contribution: %d bytes\n",
__LOG_CPU_MAX_BUF_LEN);
pr_info("log_buf_len total cpu_extra contributions: %d bytes\n",
cpu_extra);
pr_info("log_buf_len min size: %d bytes\n", __LOG_BUF_LEN);
log_buf_len_update(cpu_extra + __LOG_BUF_LEN);
}
#else /* !CONFIG_SMP */
static inline void log_buf_add_cpu(void) {}
#endif /* CONFIG_SMP */
static void __init set_percpu_data_ready(void)
{
printk_safe_init();
/* Make sure we set this flag only after printk_safe() init is done */
barrier();
__printk_percpu_data_ready = true;
}
static unsigned int __init add_to_rb(struct printk_ringbuffer *rb,
struct printk_record *r)
{
struct prb_reserved_entry e;
struct printk_record dest_r;
prb_rec_init_wr(&dest_r, r->info->text_len);
if (!prb_reserve(&e, rb, &dest_r))
return 0;
memcpy(&dest_r.text_buf[0], &r->text_buf[0], r->info->text_len);
dest_r.info->text_len = r->info->text_len;
dest_r.info->facility = r->info->facility;
dest_r.info->level = r->info->level;
dest_r.info->flags = r->info->flags;
dest_r.info->ts_nsec = r->info->ts_nsec;
dest_r.info->caller_id = r->info->caller_id;
memcpy(&dest_r.info->dev_info, &r->info->dev_info, sizeof(dest_r.info->dev_info));
prb_final_commit(&e);
return prb_record_text_space(&e);
}
static char setup_text_buf[LOG_LINE_MAX] __initdata;
void __init setup_log_buf(int early)
{
struct printk_info *new_infos;
unsigned int new_descs_count;
struct prb_desc *new_descs;
struct printk_info info;
struct printk_record r;
size_t new_descs_size;
size_t new_infos_size;
unsigned long flags;
char *new_log_buf;
unsigned int free;
u64 seq;
/*
* Some archs call setup_log_buf() multiple times - first is very
* early, e.g. from setup_arch(), and second - when percpu_areas
* are initialised.
*/
if (!early)
set_percpu_data_ready();
if (log_buf != __log_buf)
return;
if (!early && !new_log_buf_len)
log_buf_add_cpu();
if (!new_log_buf_len)
return;
new_descs_count = new_log_buf_len >> PRB_AVGBITS;
if (new_descs_count == 0) {
pr_err("new_log_buf_len: %lu too small\n", new_log_buf_len);
return;
}
new_log_buf = memblock_alloc(new_log_buf_len, LOG_ALIGN);
if (unlikely(!new_log_buf)) {
pr_err("log_buf_len: %lu text bytes not available\n",
new_log_buf_len);
return;
}
new_descs_size = new_descs_count * sizeof(struct prb_desc);
new_descs = memblock_alloc(new_descs_size, LOG_ALIGN);
if (unlikely(!new_descs)) {
pr_err("log_buf_len: %zu desc bytes not available\n",
new_descs_size);
goto err_free_log_buf;
}
new_infos_size = new_descs_count * sizeof(struct printk_info);
new_infos = memblock_alloc(new_infos_size, LOG_ALIGN);
if (unlikely(!new_infos)) {
pr_err("log_buf_len: %zu info bytes not available\n",
new_infos_size);
goto err_free_descs;
}
prb_rec_init_rd(&r, &info, &setup_text_buf[0], sizeof(setup_text_buf));
prb_init(&printk_rb_dynamic,
new_log_buf, ilog2(new_log_buf_len),
new_descs, ilog2(new_descs_count),
new_infos);
printk_safe_enter_irqsave(flags);
log_buf_len = new_log_buf_len;
log_buf = new_log_buf;
new_log_buf_len = 0;
free = __LOG_BUF_LEN;
prb_for_each_record(0, &printk_rb_static, seq, &r)
free -= add_to_rb(&printk_rb_dynamic, &r);
/*
* This is early enough that everything is still running on the
* boot CPU and interrupts are disabled. So no new messages will
* appear during the transition to the dynamic buffer.
*/
prb = &printk_rb_dynamic;
printk_safe_exit_irqrestore(flags);
if (seq != prb_next_seq(&printk_rb_static)) {
pr_err("dropped %llu messages\n",
prb_next_seq(&printk_rb_static) - seq);
}
pr_info("log_buf_len: %u bytes\n", log_buf_len);
pr_info("early log buf free: %u(%u%%)\n",
free, (free * 100) / __LOG_BUF_LEN);
return;
err_free_descs:
memblock_free(__pa(new_descs), new_descs_size);
err_free_log_buf:
memblock_free(__pa(new_log_buf), new_log_buf_len);
}
static bool __read_mostly ignore_loglevel;
static int __init ignore_loglevel_setup(char *str)
{
ignore_loglevel = true;
pr_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 (prints all kernel messages to the console)");
static bool suppress_message_printing(int level)
{
return (level >= console_loglevel && !ignore_loglevel);
}
#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 0;
}
early_param("boot_delay", boot_delay_setup);
static void boot_delay_msec(int level)
{
unsigned long long k;
unsigned long timeout;
if ((boot_delay == 0 || system_state >= SYSTEM_RUNNING)
|| suppress_message_printing(level)) {
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(int level)
{
}
#endif
static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME);
module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
static size_t print_syslog(unsigned int level, char *buf)
{
return sprintf(buf, "<%u>", level);
}
static size_t print_time(u64 ts, char *buf)
{
unsigned long rem_nsec = do_div(ts, 1000000000);
return sprintf(buf, "[%5lu.%06lu]",
(unsigned long)ts, rem_nsec / 1000);
}
#ifdef CONFIG_PRINTK_CALLER
static size_t print_caller(u32 id, char *buf)
{
char caller[12];
snprintf(caller, sizeof(caller), "%c%u",
id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
return sprintf(buf, "[%6s]", caller);
}
#else
#define print_caller(id, buf) 0
#endif
static size_t info_print_prefix(const struct printk_info *info, bool syslog,
bool time, char *buf)
{
size_t len = 0;
if (syslog)
len = print_syslog((info->facility << 3) | info->level, buf);
if (time)
len += print_time(info->ts_nsec, buf + len);
len += print_caller(info->caller_id, buf + len);
if (IS_ENABLED(CONFIG_PRINTK_CALLER) || time) {
buf[len++] = ' ';
buf[len] = '\0';
}
return len;
}
/*
* Prepare the record for printing. The text is shifted within the given
* buffer to avoid a need for another one. The following operations are
* done:
*
* - Add prefix for each line.
* - Drop truncated lines that no longer fit into the buffer.
* - Add the trailing newline that has been removed in vprintk_store().
* - Add a string terminator.
*
* Since the produced string is always terminated, the maximum possible
* return value is @r->text_buf_size - 1;
*
* Return: The length of the updated/prepared text, including the added
* prefixes and the newline. The terminator is not counted. The dropped
* line(s) are not counted.
*/
static size_t record_print_text(struct printk_record *r, bool syslog,
bool time)
{
size_t text_len = r->info->text_len;
size_t buf_size = r->text_buf_size;
char *text = r->text_buf;
char prefix[PREFIX_MAX];
bool truncated = false;
size_t prefix_len;
size_t line_len;
size_t len = 0;
char *next;
/*
* If the message was truncated because the buffer was not large
* enough, treat the available text as if it were the full text.
*/
if (text_len > buf_size)
text_len = buf_size;
prefix_len = info_print_prefix(r->info, syslog, time, prefix);
/*
* @text_len: bytes of unprocessed text
* @line_len: bytes of current line _without_ newline
* @text: pointer to beginning of current line
* @len: number of bytes prepared in r->text_buf
*/
for (;;) {
next = memchr(text, '\n', text_len);
if (next) {
line_len = next - text;
} else {
/* Drop truncated line(s). */
if (truncated)
break;
line_len = text_len;
}
/*
* Truncate the text if there is not enough space to add the
* prefix and a trailing newline and a terminator.
*/
if (len + prefix_len + text_len + 1 + 1 > buf_size) {
/* Drop even the current line if no space. */
if (len + prefix_len + line_len + 1 + 1 > buf_size)
break;
text_len = buf_size - len - prefix_len - 1 - 1;
truncated = true;
}
memmove(text + prefix_len, text, text_len);
memcpy(text, prefix, prefix_len);
/*
* Increment the prepared length to include the text and
* prefix that were just moved+copied. Also increment for the
* newline at the end of this line. If this is the last line,
* there is no newline, but it will be added immediately below.
*/
len += prefix_len + line_len + 1;
if (text_len == line_len) {
/*
* This is the last line. Add the trailing newline
* removed in vprintk_store().
*/
text[prefix_len + line_len] = '\n';
break;
}
/*
* Advance beyond the added prefix and the related line with
* its newline.
*/
text += prefix_len + line_len + 1;
/*
* The remaining text has only decreased by the line with its
* newline.
*
* Note that @text_len can become zero. It happens when @text
* ended with a newline (either due to truncation or the
* original string ending with "\n\n"). The loop is correctly
* repeated and (if not truncated) an empty line with a prefix
* will be prepared.
*/
text_len -= line_len + 1;
}
/*
* If a buffer was provided, it will be terminated. Space for the
* string terminator is guaranteed to be available. The terminator is
* not counted in the return value.
*/
if (buf_size > 0)
r->text_buf[len] = 0;
return len;
}
static size_t get_record_print_text_size(struct printk_info *info,
unsigned int line_count,
bool syslog, bool time)
{
char prefix[PREFIX_MAX];
size_t prefix_len;
prefix_len = info_print_prefix(info, syslog, time, prefix);
/*
* Each line will be preceded with a prefix. The intermediate
* newlines are already within the text, but a final trailing
* newline will be added.
*/
return ((prefix_len * line_count) + info->text_len + 1);
}
/*
* Beginning with @start_seq, find the first record where it and all following
* records up to (but not including) @max_seq fit into @size.
*
* @max_seq is simply an upper bound and does not need to exist. If the caller
* does not require an upper bound, -1 can be used for @max_seq.
*/
static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size,
bool syslog, bool time)
{
struct printk_info info;
unsigned int line_count;
size_t len = 0;
u64 seq;
/* Determine the size of the records up to @max_seq. */
prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
if (info.seq >= max_seq)
break;
len += get_record_print_text_size(&info, line_count, syslog, time);
}
/*
* Adjust the upper bound for the next loop to avoid subtracting
* lengths that were never added.
*/
if (seq < max_seq)
max_seq = seq;
/*
* Move first record forward until length fits into the buffer. Ignore
* newest messages that were not counted in the above cycle. Messages
* might appear and get lost in the meantime. This is a best effort
* that prevents an infinite loop that could occur with a retry.
*/
prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
if (len <= size || info.seq >= max_seq)
break;
len -= get_record_print_text_size(&info, line_count, syslog, time);
}
return seq;
}
static int syslog_print(char __user *buf, int size)
{
struct printk_info info;
struct printk_record r;
char *text;
int len = 0;
text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
if (!text)
return -ENOMEM;
prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
while (size > 0) {
size_t n;
size_t skip;
printk_safe_enter_irq();
raw_spin_lock(&syslog_lock);
if (!prb_read_valid(prb, syslog_seq, &r)) {
raw_spin_unlock(&syslog_lock);
printk_safe_exit_irq();
break;
}
if (r.info->seq != syslog_seq) {
/* message is gone, move to next valid one */
syslog_seq = r.info->seq;
syslog_partial = 0;
}
/*
* To keep reading/counting partial line consistent,
* use printk_time value as of the beginning of a line.
*/
if (!syslog_partial)
syslog_time = printk_time;
skip = syslog_partial;
n = record_print_text(&r, true, syslog_time);
if (n - syslog_partial <= size) {
/* message fits into buffer, move forward */
syslog_seq = r.info->seq + 1;
n -= syslog_partial;
syslog_partial = 0;
} else if (!len){
/* partial read(), remember position */
n = size;
syslog_partial += n;
} else
n = 0;
raw_spin_unlock(&syslog_lock);
printk_safe_exit_irq();
if (!n)
break;
if (copy_to_user(buf, text + skip, n)) {
if (!len)
len = -EFAULT;
break;
}
len += n;
size -= n;
buf += n;
}
kfree(text);
return len;
}
static int syslog_print_all(char __user *buf, int size, bool clear)
{
struct printk_info info;
struct printk_record r;
char *text;
int len = 0;
u64 seq;
bool time;
text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
if (!text)
return -ENOMEM;
time = printk_time;
printk_safe_enter_irq();
/*
* Find first record that fits, including all following records,
* into the user-provided buffer for this dump.
*/
seq = find_first_fitting_seq(latched_seq_read_nolock(&clear_seq), -1,
size, true, time);
prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
len = 0;
prb_for_each_record(seq, prb, seq, &r) {
int textlen;
textlen = record_print_text(&r, true, time);
if (len + textlen > size) {
seq--;
break;
}
printk_safe_exit_irq();
if (copy_to_user(buf + len, text, textlen))
len = -EFAULT;
else
len += textlen;
printk_safe_enter_irq();
if (len < 0)
break;
}
if (clear) {
raw_spin_lock(&syslog_lock);
latched_seq_write(&clear_seq, seq);
raw_spin_unlock(&syslog_lock);
}
printk_safe_exit_irq();
kfree(text);
return len;
}
static void syslog_clear(void)
{
printk_safe_enter_irq();
raw_spin_lock(&syslog_lock);
latched_seq_write(&clear_seq, prb_next_seq(prb));
raw_spin_unlock(&syslog_lock);
printk_safe_exit_irq();
}
/* Return a consistent copy of @syslog_seq. */
static u64 read_syslog_seq_irq(void)
{
u64 seq;
raw_spin_lock_irq(&syslog_lock);
seq = syslog_seq;
raw_spin_unlock_irq(&syslog_lock);
return seq;
}
int do_syslog(int type, char __user *buf, int len, int source)
{
struct printk_info info;
bool clear = false;
static int saved_console_loglevel = LOGLEVEL_DEFAULT;
int error;
error = check_syslog_permissions(type, source);
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 */
if (!buf || len < 0)
return -EINVAL;
if (!len)
return 0;
if (!access_ok(buf, len))
return -EFAULT;
error = wait_event_interruptible(log_wait,
prb_read_valid(prb, read_syslog_seq_irq(), NULL));
if (error)
return error;
error = syslog_print(buf, len);
break;
/* Read/clear last kernel messages */
case SYSLOG_ACTION_READ_CLEAR:
clear = true;
fallthrough;
/* Read last kernel messages */
case SYSLOG_ACTION_READ_ALL:
if (!buf || len < 0)
return -EINVAL;
if (!len)
return 0;
if (!access_ok(buf, len))
return -EFAULT;
error = syslog_print_all(buf, len, clear);
break;
/* Clear ring buffer */
case SYSLOG_ACTION_CLEAR:
syslog_clear();
break;
/* Disable logging to console */
case SYSLOG_ACTION_CONSOLE_OFF:
if (saved_console_loglevel == LOGLEVEL_DEFAULT)
saved_console_loglevel = console_loglevel;
console_loglevel = minimum_console_loglevel;
break;
/* Enable logging to console */
case SYSLOG_ACTION_CONSOLE_ON:
if (saved_console_loglevel != LOGLEVEL_DEFAULT) {
console_loglevel = saved_console_loglevel;
saved_console_loglevel = LOGLEVEL_DEFAULT;
}
break;
/* Set level of messages printed to console */
case SYSLOG_ACTION_CONSOLE_LEVEL:
if (len < 1 || len > 8)
return -EINVAL;
if (len < minimum_console_loglevel)
len = minimum_console_loglevel;
console_loglevel = len;
/* Implicitly re-enable logging to console */
saved_console_loglevel = LOGLEVEL_DEFAULT;
break;
/* Number of chars in the log buffer */
case SYSLOG_ACTION_SIZE_UNREAD:
printk_safe_enter_irq();
raw_spin_lock(&syslog_lock);
if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
/* No unread messages. */
raw_spin_unlock(&syslog_lock);
printk_safe_exit_irq();
return 0;
}
if (info.seq != syslog_seq) {
/* messages are gone, move to first one */
syslog_seq = info.seq;
syslog_partial = 0;
}
if (source == SYSLOG_FROM_PROC) {
/*
* Short-cut for poll(/"proc/kmsg") which simply checks
* for pending data, not the size; return the count of
* records, not the length.
*/
error = prb_next_seq(prb) - syslog_seq;
} else {
bool time = syslog_partial ? syslog_time : printk_time;
unsigned int line_count;
u64 seq;
prb_for_each_info(syslog_seq, prb, seq, &info,
&line_count) {
error += get_record_print_text_size(&info, line_count,
true, time);
time = printk_time;
}
error -= syslog_partial;
}
raw_spin_unlock(&syslog_lock);
printk_safe_exit_irq();
break;
/* Size of the log buffer */
case SYSLOG_ACTION_SIZE_BUFFER:
error = log_buf_len;
break;
default:
error = -EINVAL;
break;
}
return error;
}
SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
{
return do_syslog(type, buf, len, SYSLOG_FROM_READER);
}
/*
* Special console_lock variants that help to reduce the risk of soft-lockups.
* They allow to pass console_lock to another printk() call using a busy wait.
*/
#ifdef CONFIG_LOCKDEP
static struct lockdep_map console_owner_dep_map = {
.name = "console_owner"
};
#endif
static DEFINE_RAW_SPINLOCK(console_owner_lock);
static struct task_struct *console_owner;
static bool console_waiter;
/**
* console_lock_spinning_enable - mark beginning of code where another
* thread might safely busy wait
*
* This basically converts console_lock into a spinlock. This marks
* the section where the console_lock owner can not sleep, because
* there may be a waiter spinning (like a spinlock). Also it must be
* ready to hand over the lock at the end of the section.
*/
static void console_lock_spinning_enable(void)
{
raw_spin_lock(&console_owner_lock);
console_owner = current;
raw_spin_unlock(&console_owner_lock);
/* The waiter may spin on us after setting console_owner */
spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
}
/**
* console_lock_spinning_disable_and_check - mark end of code where another
* thread was able to busy wait and check if there is a waiter
*
* This is called at the end of the section where spinning is allowed.
* It has two functions. First, it is a signal that it is no longer
* safe to start busy waiting for the lock. Second, it checks if
* there is a busy waiter and passes the lock rights to her.
*
* Important: Callers lose the lock if there was a busy waiter.
* They must not touch items synchronized by console_lock
* in this case.
*
* Return: 1 if the lock rights were passed, 0 otherwise.
*/
static int console_lock_spinning_disable_and_check(void)
{
int waiter;
raw_spin_lock(&console_owner_lock);
waiter = READ_ONCE(console_waiter);
console_owner = NULL;
raw_spin_unlock(&console_owner_lock);
if (!waiter) {
spin_release(&console_owner_dep_map, _THIS_IP_);
return 0;
}
/* The waiter is now free to continue */
WRITE_ONCE(console_waiter, false);
spin_release(&console_owner_dep_map, _THIS_IP_);
/*
* Hand off console_lock to waiter. The waiter will perform
* the up(). After this, the waiter is the console_lock owner.
*/
mutex_release(&console_lock_dep_map, _THIS_IP_);
return 1;
}
/**
* console_trylock_spinning - try to get console_lock by busy waiting
*
* This allows to busy wait for the console_lock when the current
* owner is running in specially marked sections. It means that
* the current owner is running and cannot reschedule until it
* is ready to lose the lock.
*
* Return: 1 if we got the lock, 0 othrewise
*/
static int console_trylock_spinning(void)
{
struct task_struct *owner = NULL;
bool waiter;
bool spin = false;
unsigned long flags;
if (console_trylock())
return 1;
printk_safe_enter_irqsave(flags);
raw_spin_lock(&console_owner_lock);
owner = READ_ONCE(console_owner);
waiter = READ_ONCE(console_waiter);
if (!waiter && owner && owner != current) {
WRITE_ONCE(console_waiter, true);
spin = true;
}
raw_spin_unlock(&console_owner_lock);
/*
* If there is an active printk() writing to the
* consoles, instead of having it write our data too,
* see if we can offload that load from the active
* printer, and do some printing ourselves.
* Go into a spin only if there isn't already a waiter
* spinning, and there is an active printer, and
* that active printer isn't us (recursive printk?).
*/
if (!spin) {
printk_safe_exit_irqrestore(flags);
return 0;
}
/* We spin waiting for the owner to release us */
spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
/* Owner will clear console_waiter on hand off */
while (READ_ONCE(console_waiter))
cpu_relax();
spin_release(&console_owner_dep_map, _THIS_IP_);
printk_safe_exit_irqrestore(flags);
/*
* The owner passed the console lock to us.
* Since we did not spin on console lock, annotate
* this as a trylock. Otherwise lockdep will
* complain.
*/
mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_);
return 1;
}
/*
* 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(const char *ext_text, size_t ext_len,
const char *text, size_t len)
{
static char dropped_text[64];
size_t dropped_len = 0;
struct console *con;
trace_console_rcuidle(text, len);
if (!console_drivers)
return;
if (console_dropped) {
dropped_len = snprintf(dropped_text, sizeof(dropped_text),
"** %lu printk messages dropped **\n",
console_dropped);
console_dropped = 0;
}
for_each_console(con) {
if (exclusive_console && con != exclusive_console)
continue;
if (!(con->flags & CON_ENABLED))
continue;
if (!con->write)
continue;
if (!cpu_online(smp_processor_id()) &&
!(con->flags & CON_ANYTIME))
continue;
if (con->flags & CON_EXTENDED)
con->write(con, ext_text, ext_len);
else {
if (dropped_len)
con->write(con, dropped_text, dropped_len);
con->write(con, text, len);
}
}
}
int printk_delay_msec __read_mostly;
static inline void printk_delay(void)
{
if (unlikely(printk_delay_msec)) {
int m = printk_delay_msec;
while (m--) {
mdelay(1);
touch_nmi_watchdog();
}
}
}
static inline u32 printk_caller_id(void)
{
return in_task() ? task_pid_nr(current) :
0x80000000 + raw_smp_processor_id();
}
/**
* parse_prefix - Parse level and control flags.
*
* @text: The terminated text message.
* @level: A pointer to the current level value, will be updated.
* @lflags: A pointer to the current log flags, will be updated.
*
* @level may be NULL if the caller is not interested in the parsed value.
* Otherwise the variable pointed to by @level must be set to
* LOGLEVEL_DEFAULT in order to be updated with the parsed value.
*
* @lflags may be NULL if the caller is not interested in the parsed value.
* Otherwise the variable pointed to by @lflags will be OR'd with the parsed
* value.
*
* Return: The length of the parsed level and control flags.
*/
static u16 parse_prefix(char *text, int *level, enum log_flags *lflags)
{
u16 prefix_len = 0;
int kern_level;
while (*text) {
kern_level = printk_get_level(text);
if (!kern_level)
break;
switch (kern_level) {
case '0' ... '7':
if (level && *level == LOGLEVEL_DEFAULT)
*level = kern_level - '0';
break;
case 'c': /* KERN_CONT */
if (lflags)
*lflags |= LOG_CONT;
}
prefix_len += 2;
text += 2;
}
return prefix_len;
}
static u16 printk_sprint(char *text, u16 size, int facility, enum log_flags *lflags,
const char *fmt, va_list args)
{
u16 text_len;
text_len = vscnprintf(text, size, fmt, args);
/* Mark and strip a trailing newline. */
if (text_len && text[text_len - 1] == '\n') {
text_len--;
*lflags |= LOG_NEWLINE;
}
/* Strip log level and control flags. */
if (facility == 0) {
u16 prefix_len;
prefix_len = parse_prefix(text, NULL, NULL);
if (prefix_len) {
text_len -= prefix_len;
memmove(text, text + prefix_len, text_len);
}
}
return text_len;
}
__printf(4, 0)
int vprintk_store(int facility, int level,
const struct dev_printk_info *dev_info,
const char *fmt, va_list args)
{
const u32 caller_id = printk_caller_id();
struct prb_reserved_entry e;
enum log_flags lflags = 0;
struct printk_record r;
u16 trunc_msg_len = 0;
char prefix_buf[8];
u16 reserve_size;
va_list args2;
u16 text_len;
u64 ts_nsec;
/*
* Since the duration of printk() can vary depending on the message
* and state of the ringbuffer, grab the timestamp now so that it is
* close to the call of printk(). This provides a more deterministic
* timestamp with respect to the caller.
*/
ts_nsec = local_clock();
/*
* The sprintf needs to come first since the syslog prefix might be
* passed in as a parameter. An extra byte must be reserved so that
* later the vscnprintf() into the reserved buffer has room for the
* terminating '\0', which is not counted by vsnprintf().
*/
va_copy(args2, args);
reserve_size = vsnprintf(&prefix_buf[0], sizeof(prefix_buf), fmt, args2) + 1;
va_end(args2);
if (reserve_size > LOG_LINE_MAX)
reserve_size = LOG_LINE_MAX;
/* Extract log level or control flags. */
if (facility == 0)
parse_prefix(&prefix_buf[0], &level, &lflags);
if (level == LOGLEVEL_DEFAULT)
level = default_message_loglevel;
if (dev_info)
lflags |= LOG_NEWLINE;
if (lflags & LOG_CONT) {
prb_rec_init_wr(&r, reserve_size);
if (prb_reserve_in_last(&e, prb, &r, caller_id, LOG_LINE_MAX)) {
text_len = printk_sprint(&r.text_buf[r.info->text_len], reserve_size,
facility, &lflags, fmt, args);
r.info->text_len += text_len;
if (lflags & LOG_NEWLINE) {
r.info->flags |= LOG_NEWLINE;
prb_final_commit(&e);
} else {
prb_commit(&e);
}
return text_len;
}
}
/*
* Explicitly initialize the record before every prb_reserve() call.
* prb_reserve_in_last() and prb_reserve() purposely invalidate the
* structure when they fail.
*/
prb_rec_init_wr(&r, reserve_size);
if (!prb_reserve(&e, prb, &r)) {
/* truncate the message if it is too long for empty buffer */
truncate_msg(&reserve_size, &trunc_msg_len);
prb_rec_init_wr(&r, reserve_size + trunc_msg_len);
if (!prb_reserve(&e, prb, &r))
return 0;
}
/* fill message */
text_len = printk_sprint(&r.text_buf[0], reserve_size, facility, &lflags, fmt, args);
if (trunc_msg_len)
memcpy(&r.text_buf[text_len], trunc_msg, trunc_msg_len);
r.info->text_len = text_len + trunc_msg_len;
r.info->facility = facility;
r.info->level = level & 7;
r.info->flags = lflags & 0x1f;
r.info->ts_nsec = ts_nsec;
r.info->caller_id = caller_id;
if (dev_info)
memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));
/* A message without a trailing newline can be continued. */
if (!(lflags & LOG_NEWLINE))
prb_commit(&e);
else
prb_final_commit(&e);
return (text_len + trunc_msg_len);
}
asmlinkage int vprintk_emit(int facility, int level,
const struct dev_printk_info *dev_info,
const char *fmt, va_list args)
{
int printed_len;
bool in_sched = false;
unsigned long flags;
/* Suppress unimportant messages after panic happens */
if (unlikely(suppress_printk))
return 0;
if (level == LOGLEVEL_SCHED) {
level = LOGLEVEL_DEFAULT;
in_sched = true;
}
boot_delay_msec(level);
printk_delay();
printk_safe_enter_irqsave(flags);
printed_len = vprintk_store(facility, level, dev_info, fmt, args);
printk_safe_exit_irqrestore(flags);
/* If called from the scheduler, we can not call up(). */
if (!in_sched) {
/*
* Disable preemption to avoid being preempted while holding
* console_sem which would prevent anyone from printing to
* console
*/
preempt_disable();
/*
* Try to acquire and then immediately release the console
* semaphore. The release will print out buffers and wake up
* /dev/kmsg and syslog() users.
*/
if (console_trylock_spinning())
console_unlock();
preempt_enable();
}
wake_up_klogd();
return printed_len;
}
EXPORT_SYMBOL(vprintk_emit);
int vprintk_default(const char *fmt, va_list args)
{
return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
}
EXPORT_SYMBOL_GPL(vprintk_default);
/**
* 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.
*
* 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 __visible int printk(const char *fmt, ...)
{
va_list args;
int r;
va_start(args, fmt);
r = vprintk(fmt, args);
va_end(args);
return r;
}
EXPORT_SYMBOL(printk);
#else /* CONFIG_PRINTK */
#define CONSOLE_LOG_MAX 0
#define printk_time false
#define prb_read_valid(rb, seq, r) false
#define prb_first_valid_seq(rb) 0
static u64 syslog_seq;
static u64 console_seq;
static u64 exclusive_console_stop_seq;
static unsigned long console_dropped;
static size_t record_print_text(const struct printk_record *r,
bool syslog, bool time)
{
return 0;
}
static ssize_t info_print_ext_header(char *buf, size_t size,
struct printk_info *info)
{
return 0;
}
static ssize_t msg_print_ext_body(char *buf, size_t size,
char *text, size_t text_len,
struct dev_printk_info *dev_info) { return 0; }
static void console_lock_spinning_enable(void) { }
static int console_lock_spinning_disable_and_check(void) { return 0; }
static void call_console_drivers(const char *ext_text, size_t ext_len,
const char *text, size_t len) {}
static bool suppress_message_printing(int level) { return false; }
#endif /* CONFIG_PRINTK */
#ifdef CONFIG_EARLY_PRINTK
struct console *early_console;
asmlinkage __visible void early_printk(const char *fmt, ...)
{
va_list ap;
char buf[512];
int n;
if (!early_console)
return;
va_start(ap, fmt);
n = vscnprintf(buf, sizeof(buf), fmt, ap);
va_end(ap);
early_console->write(early_console, buf, n);
}
#endif
static int __add_preferred_console(char *name, int idx, char *options,
char *brl_options, bool user_specified)
{
struct console_cmdline *c;
int i;
/*
* See if this tty is not yet registered, and
* if we have a slot free.
*/
for (i = 0, c = console_cmdline;
i < MAX_CMDLINECONSOLES && c->name[0];
i++, c++) {
if (strcmp(c->name, name) == 0 && c->index == idx) {
if (!brl_options)
preferred_console = i;
if (user_specified)
c->user_specified = true;
return 0;
}
}
if (i == MAX_CMDLINECONSOLES)
return -E2BIG;
if (!brl_options)
preferred_console = i;
strlcpy(c->name, name, sizeof(c->name));
c->options = options;
c->user_specified = user_specified;
braille_set_options(c, brl_options);
c->index = idx;
return 0;
}
static int __init console_msg_format_setup(char *str)
{
if (!strcmp(str, "syslog"))
console_msg_format = MSG_FORMAT_SYSLOG;
if (!strcmp(str, "default"))
console_msg_format = MSG_FORMAT_DEFAULT;
return 1;
}
__setup("console_msg_format=", console_msg_format_setup);
/*
* Set up a console. Called via do_early_param() in init/main.c
* for each "console=" parameter in the boot command line.
*/
static int __init console_setup(char *str)
{
char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for "ttyS" */
char *s, *options, *brl_options = NULL;
int idx;
/*
* console="" or console=null have been suggested as a way to
* disable console output. Use ttynull that has been created
* for exactly this purpose.
*/
if (str[0] == 0 || strcmp(str, "null") == 0) {
__add_preferred_console("ttynull", 0, NULL, NULL, true);
return 1;
}
if (_braille_console_setup(&str, &brl_options))
return 1;
/*
* 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;
options = strchr(str, ',');
if (options)
*(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 (isdigit(*s) || *s == ',')
break;
idx = simple_strtoul(s, NULL, 10);
*s = 0;
__add_preferred_console(buf, idx, options, brl_options, true);
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, false);
}
bool console_suspend_enabled = true;
EXPORT_SYMBOL(console_suspend_enabled);
static int __init console_suspend_disable(char *str)
{
console_suspend_enabled = false;
return 1;
}
__setup("no_console_suspend", console_suspend_disable);
module_param_named(console_suspend, console_suspend_enabled,
bool, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
" and hibernate operations");
/**
* suspend_console - suspend the console subsystem
*
* This disables printk() while we go into suspend states
*/
void suspend_console(void)
{
if (!console_suspend_enabled)
return;
pr_info("Suspending console(s) (use no_console_suspend to debug)\n");
console_lock();
console_suspended = 1;
up_console_sem();
}
void resume_console(void)
{
if (!console_suspend_enabled)
return;
down_console_sem();
console_suspended = 0;
console_unlock();
}
/**
* console_cpu_notify - print deferred console messages after CPU hotplug
* @cpu: unused
*
* If printk() is called from a CPU that is not online yet, the messages
* will be printed on the console only if there are CON_ANYTIME consoles.
* This function is called when a new CPU comes online (or fails to come
* up) or goes offline.
*/
static int console_cpu_notify(unsigned int cpu)
{
if (!cpuhp_tasks_frozen) {
/* If trylock fails, someone else is doing the printing */
if (console_trylock())
console_unlock();
}
return 0;
}
/**
* console_lock - lock the console system for exclusive use.
*
* Acquires a lock which guarantees that the caller has
* exclusive access to the console system and the console_drivers list.
*
* Can sleep, returns nothing.
*/
void console_lock(void)
{
might_sleep();
down_console_sem();
if (console_suspended)
return;
console_locked = 1;
console_may_schedule = 1;
}
EXPORT_SYMBOL(console_lock);
/**
* console_trylock - try to lock the console system for exclusive use.
*
* Try to acquire a lock which guarantees that the caller has exclusive
* access to the console system and the console_drivers list.
*
* returns 1 on success, and 0 on failure to acquire the lock.
*/
int console_trylock(void)
{
if (down_trylock_console_sem())
return 0;
if (console_suspended) {
up_console_sem();
return 0;
}
console_locked = 1;
console_may_schedule = 0;
return 1;
}
EXPORT_SYMBOL(console_trylock);
int is_console_locked(void)
{
return console_locked;
}
EXPORT_SYMBOL(is_console_locked);
/*
* Check if we have any console that is capable of printing while cpu is
* booting or shutting down. Requires console_sem.
*/
static int have_callable_console(void)
{
struct console *con;
for_each_console(con)
if ((con->flags & CON_ENABLED) &&
(con->flags & CON_ANYTIME))
return 1;
return 0;
}
/*
* 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(void)
{
return cpu_online(raw_smp_processor_id()) || have_callable_console();
}
/**
* console_unlock - unlock the console system
*
* Releases the console_lock which the caller holds on the console system
* and the console driver list.
*
* While the console_lock was held, console output may have been buffered
* by printk(). If this is the case, console_unlock(); emits
* the output prior to releasing the lock.
*
* If there is output waiting, we wake /dev/kmsg and syslog() users.
*
* console_unlock(); may be called from any context.
*/
void console_unlock(void)
{
static char ext_text[CONSOLE_EXT_LOG_MAX];
static char text[CONSOLE_LOG_MAX];
unsigned long flags;
bool do_cond_resched, retry;
struct printk_info info;
struct printk_record r;
if (console_suspended) {
up_console_sem();
return;
}
prb_rec_init_rd(&r, &info, text, sizeof(text));
/*
* Console drivers are called with interrupts disabled, so
* @console_may_schedule should be cleared before; however, we may
* end up dumping a lot of lines, for example, if called from
* console registration path, and should invoke cond_resched()
* between lines if allowable. Not doing so can cause a very long
* scheduling stall on a slow console leading to RCU stall and
* softlockup warnings which exacerbate the issue with more
* messages practically incapacitating the system.
*
* console_trylock() is not able to detect the preemptive
* context reliably. Therefore the value must be stored before
* and cleared after the "again" goto label.
*/
do_cond_resched = console_may_schedule;
again:
console_may_schedule = 0;
/*
* We released the console_sem lock, so we need to recheck if
* cpu is online and (if not) is there at least one CON_ANYTIME
* console.
*/
if (!can_use_console()) {
console_locked = 0;
up_console_sem();
return;
}
for (;;) {
size_t ext_len = 0;
size_t len;
printk_safe_enter_irqsave(flags);
skip:
if (!prb_read_valid(prb, console_seq, &r))
break;
if (console_seq != r.info->seq) {
console_dropped += r.info->seq - console_seq;
console_seq = r.info->seq;
}
if (suppress_message_printing(r.info->level)) {
/*
* Skip record we have buffered and already printed
* directly to the console when we received it, and
* record that has level above the console loglevel.
*/
console_seq++;
goto skip;
}
/* Output to all consoles once old messages replayed. */
if (unlikely(exclusive_console &&
console_seq >= exclusive_console_stop_seq)) {
exclusive_console = NULL;
}
/*
* Handle extended console text first because later
* record_print_text() will modify the record buffer in-place.
*/
if (nr_ext_console_drivers) {
ext_len = info_print_ext_header(ext_text,
sizeof(ext_text),
r.info);
ext_len += msg_print_ext_body(ext_text + ext_len,
sizeof(ext_text) - ext_len,
&r.text_buf[0],
r.info->text_len,
&r.info->dev_info);
}
len = record_print_text(&r,
console_msg_format & MSG_FORMAT_SYSLOG,
printk_time);
console_seq++;
/*
* While actively printing out messages, if another printk()
* were to occur on another CPU, it may wait for this one to
* finish. This task can not be preempted if there is a
* waiter waiting to take over.
*/
console_lock_spinning_enable();
stop_critical_timings(); /* don't trace print latency */
call_console_drivers(ext_text, ext_len, text, len);
start_critical_timings();
if (console_lock_spinning_disable_and_check()) {
printk_safe_exit_irqrestore(flags);
return;
}
printk_safe_exit_irqrestore(flags);
if (do_cond_resched)
cond_resched();
}
console_locked = 0;
up_console_sem();
/*
* Someone could have filled up the buffer again, so re-check if there's
* something to flush. In case we cannot trylock the console_sem again,
* there's a new owner and the console_unlock() from them will do the
* flush, no worries.
*/
retry = prb_read_valid(prb, console_seq, NULL);
printk_safe_exit_irqrestore(flags);
if (retry && console_trylock())
goto again;
}
EXPORT_SYMBOL(console_unlock);
/**
* 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 console_lock();.
*/
void __sched console_conditional_schedule(void)
{
if (console_may_schedule)
cond_resched();
}
EXPORT_SYMBOL(console_conditional_schedule);
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
console_lock();
console_locked = 1;
console_may_schedule = 0;
for_each_console(c)
if ((c->flags & CON_ENABLED) && c->unblank)
c->unblank();
console_unlock();
}
/**
* console_flush_on_panic - flush console content on panic
* @mode: flush all messages in buffer or just the pending ones
*
* Immediately output all pending messages no matter what.
*/
void console_flush_on_panic(enum con_flush_mode mode)
{
/*
* If someone else is holding the console lock, trylock will fail
* and may_schedule may be set. Ignore and proceed to unlock so
* that messages are flushed out. As this can be called from any
* context and we don't want to get preempted while flushing,
* ensure may_schedule is cleared.
*/
console_trylock();
console_may_schedule = 0;
if (mode == CONSOLE_REPLAY_ALL) {
unsigned long flags;
printk_safe_enter_irqsave(flags);
console_seq = prb_first_valid_seq(prb);
printk_safe_exit_irqrestore(flags);
}
console_unlock();
}
/*
* 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;
console_lock();
for_each_console(c) {
if (!c->device)
continue;
driver = c->device(c, index);
if (driver)
break;
}
console_unlock();
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)
{
console_lock();
console->flags &= ~CON_ENABLED;
console_unlock();
}
EXPORT_SYMBOL(console_stop);
void console_start(struct console *console)
{
console_lock();
console->flags |= CON_ENABLED;
console_unlock();
}
EXPORT_SYMBOL(console_start);
static int __read_mostly keep_bootcon;
static int __init keep_bootcon_setup(char *str)
{
keep_bootcon = 1;
pr_info("debug: skip boot console de-registration.\n");
return 0;
}
early_param("keep_bootcon", keep_bootcon_setup);
/*
* This is called by register_console() to try to match
* the newly registered console with any of the ones selected
* by either the command line or add_preferred_console() and
* setup/enable it.
*
* Care need to be taken with consoles that are statically
* enabled such as netconsole
*/
static int try_enable_new_console(struct console *newcon, bool user_specified)
{
struct console_cmdline *c;
int i, err;
for (i = 0, c = console_cmdline;
i < MAX_CMDLINECONSOLES && c->name[0];
i++, c++) {
if (c->user_specified != user_specified)
continue;
if (!newcon->match ||
newcon->match(newcon, c->name, c->index, c->options) != 0) {
/* default matching */
BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
if (strcmp(c->name, newcon->name) != 0)
continue;
if (newcon->index >= 0 &&
newcon->index != c->index)
continue;
if (newcon->index < 0)
newcon->index = c->index;
if (_braille_register_console(newcon, c))
return 0;
if (newcon->setup &&
(err = newcon->setup(newcon, c->options)) != 0)
return err;
}
newcon->flags |= CON_ENABLED;
if (i == preferred_console) {
newcon->flags |= CON_CONSDEV;
has_preferred_console = true;
}
return 0;
}
/*
* Some consoles, such as pstore and netconsole, can be enabled even
* without matching. Accept the pre-enabled consoles only when match()
* and setup() had a chance to be called.
*/
if (newcon->flags & CON_ENABLED && c->user_specified == user_specified)
return 0;
return -ENOENT;
}
/*
* 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.
*
* This can happen pretty early during the boot process (because of
* early_printk) - sometimes before setup_arch() completes - be careful
* of what kernel features are used - they may not be initialised yet.
*
* There are two types of consoles - bootconsoles (early_printk) and
* "real" consoles (everything which is not a bootconsole) which are
* handled differently.
* - Any number of bootconsoles can be registered at any time.
* - As soon as a "real" console is registered, all bootconsoles
* will be unregistered automatically.
* - Once a "real" console is registered, any attempt to register a
* bootconsoles will be rejected
*/
void register_console(struct console *newcon)
{
unsigned long flags;
struct console *bcon = NULL;
int err;
for_each_console(bcon) {
if (WARN(bcon == newcon, "console '%s%d' already registered\n",
bcon->name, bcon->index))
return;
}
/*
* before we register a new CON_BOOT console, make sure we don't
* already have a valid console
*/
if (newcon->flags & CON_BOOT) {
for_each_console(bcon) {
if (!(bcon->flags & CON_BOOT)) {
pr_info("Too late to register bootconsole %s%d\n",
newcon->name, newcon->index);
return;
}
}
}
if (console_drivers && console_drivers->flags & CON_BOOT)
bcon = console_drivers;
if (!has_preferred_console || bcon || !console_drivers)
has_preferred_console = preferred_console >= 0;
/*
* 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 (!has_preferred_console) {
if (newcon->index < 0)
newcon->index = 0;
if (newcon->setup == NULL ||
newcon->setup(newcon, NULL) == 0) {
newcon->flags |= CON_ENABLED;
if (newcon->device) {
newcon->flags |= CON_CONSDEV;
has_preferred_console = true;
}
}
}
/* See if this console matches one we selected on the command line */
err = try_enable_new_console(newcon, true);
/* If not, try to match against the platform default(s) */
if (err == -ENOENT)
err = try_enable_new_console(newcon, false);
/* printk() messages are not printed to the Braille console. */
if (err || newcon->flags & CON_BRL)
return;
/*
* If we have a bootconsole, and are switching to a real console,
* don't print everything out again, since when the boot console, and
* the real console are the same physical device, it's annoying to
* see the beginning boot messages twice
*/
if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
newcon->flags &= ~CON_PRINTBUFFER;
/*
* Put this console in the list - keep the
* preferred driver at the head of the list.
*/
console_lock();
if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
newcon->next = console_drivers;
console_drivers = newcon;
if (newcon->next)
newcon->next->flags &= ~CON_CONSDEV;
/* Ensure this flag is always set for the head of the list */
newcon->flags |= CON_CONSDEV;
} else {
newcon->next = console_drivers->next;
console_drivers->next = newcon;
}
if (newcon->flags & CON_EXTENDED)
nr_ext_console_drivers++;
if (newcon->flags & CON_PRINTBUFFER) {
/*
* console_unlock(); will print out the buffered messages
* for us.
*
* We're about to replay the log buffer. Only do this to the
* just-registered console to avoid excessive message spam to
* the already-registered consoles.
*
* Set exclusive_console with disabled interrupts to reduce
* race window with eventual console_flush_on_panic() that
* ignores console_lock.
*/
exclusive_console = newcon;
exclusive_console_stop_seq = console_seq;
/* Get a consistent copy of @syslog_seq. */
raw_spin_lock_irqsave(&syslog_lock, flags);
console_seq = syslog_seq;
raw_spin_unlock_irqrestore(&syslog_lock, flags);
}
console_unlock();
console_sysfs_notify();
/*
* By unregistering the bootconsoles after we enable the real console
* we get the "console xxx enabled" message on all the consoles -
* boot consoles, real consoles, etc - this is to ensure that end
* users know there might be something in the kernel's log buffer that
* went to the bootconsole (that they do not see on the real console)
*/
pr_info("%sconsole [%s%d] enabled\n",
(newcon->flags & CON_BOOT) ? "boot" : "" ,
newcon->name, newcon->index);
if (bcon &&
((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
!keep_bootcon) {
/* We need to iterate through all boot consoles, to make
* sure we print everything out, before we unregister them.
*/
for_each_console(bcon)
if (bcon->flags & CON_BOOT)
unregister_console(bcon);
}
}
EXPORT_SYMBOL(register_console);
int unregister_console(struct console *console)
{
struct console *con;
int res;
pr_info("%sconsole [%s%d] disabled\n",
(console->flags & CON_BOOT) ? "boot" : "" ,
console->name, console->index);
res = _braille_unregister_console(console);
if (res < 0)
return res;
if (res > 0)
return 0;
res = -ENODEV;
console_lock();
if (console_drivers == console) {
console_drivers=console->next;
res = 0;
} else {
for_each_console(con) {
if (con->next == console) {
con->next = console->next;
res = 0;
break;
}
}
}
if (res)
goto out_disable_unlock;
if (console->flags & CON_EXTENDED)
nr_ext_console_drivers--;
/*
* 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;
console->flags &= ~CON_ENABLED;
console_unlock();
console_sysfs_notify();
if (console->exit)
res = console->exit(console);
return res;
out_disable_unlock:
console->flags &= ~CON_ENABLED;
console_unlock();
return res;
}
EXPORT_SYMBOL(unregister_console);
/*
* Initialize the console device. This is called *early*, so
* we can't necessarily depend on lots of kernel help here.
* Just do some early initializations, and do the complex setup
* later.
*/
void __init console_init(void)
{
int ret;
initcall_t call;
initcall_entry_t *ce;
/* Setup the default TTY line discipline. */
n_tty_init();
/*
* set up the console device so that later boot sequences can
* inform about problems etc..
*/
ce = __con_initcall_start;
trace_initcall_level("console");
while (ce < __con_initcall_end) {
call = initcall_from_entry(ce);
trace_initcall_start(call);
ret = call();
trace_initcall_finish(call, ret);
ce++;
}
}
/*
* Some boot consoles access data that is in the init section and which will
* be discarded after the initcalls have been run. To make sure that no code
* will access this data, unregister the boot consoles in a late initcall.
*
* If for some reason, such as deferred probe or the driver being a loadable
* module, the real console hasn't registered yet at this point, there will
* be a brief interval in which no messages are logged to the console, which
* makes it difficult to diagnose problems that occur during this time.
*
* To mitigate this problem somewhat, only unregister consoles whose memory
* intersects with the init section. Note that all other boot consoles will
* get unregistered when the real preferred console is registered.
*/
static int __init printk_late_init(void)
{
struct console *con;
int ret;
for_each_console(con) {
if (!(con->flags & CON_BOOT))
continue;
/* Check addresses that might be used for enabled consoles. */
if (init_section_intersects(con, sizeof(*con)) ||
init_section_contains(con->write, 0) ||
init_section_contains(con->read, 0) ||
init_section_contains(con->device, 0) ||
init_section_contains(con->unblank, 0) ||
init_section_contains(con->data, 0)) {
/*
* Please, consider moving the reported consoles out
* of the init section.
*/
pr_warn("bootconsole [%s%d] uses init memory and must be disabled even before the real one is ready\n",
con->name, con->index);
unregister_console(con);
}
}
ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,
console_cpu_notify);
WARN_ON(ret < 0);
ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "printk:online",
console_cpu_notify, NULL);
WARN_ON(ret < 0);
return 0;
}
late_initcall(printk_late_init);
#if defined CONFIG_PRINTK
/*
* Delayed printk version, for scheduler-internal messages:
*/
#define PRINTK_PENDING_WAKEUP 0x01
#define PRINTK_PENDING_OUTPUT 0x02
static DEFINE_PER_CPU(int, printk_pending);
static void wake_up_klogd_work_func(struct irq_work *irq_work)
{
int pending = __this_cpu_xchg(printk_pending, 0);
if (pending & PRINTK_PENDING_OUTPUT) {
/* If trylock fails, someone else is doing the printing */
if (console_trylock())
console_unlock();
}
if (pending & PRINTK_PENDING_WAKEUP)
wake_up_interruptible(&log_wait);
}
static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) =
IRQ_WORK_INIT_LAZY(wake_up_klogd_work_func);
void wake_up_klogd(void)
{
if (!printk_percpu_data_ready())
return;
preempt_disable();
if (waitqueue_active(&log_wait)) {
this_cpu_or(printk_pending, PRINTK_PENDING_WAKEUP);
irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
}
preempt_enable();
}
void defer_console_output(void)
{
if (!printk_percpu_data_ready())
return;
preempt_disable();
__this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
preempt_enable();
}
int vprintk_deferred(const char *fmt, va_list args)
{
int r;
r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args);
defer_console_output();
return r;
}
int printk_deferred(const char *fmt, ...)
{
va_list args;
int r;
va_start(args, fmt);
r = vprintk_deferred(fmt, args);
va_end(args);
return r;
}
/*
* 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(const char *func)
{
return ___ratelimit(&printk_ratelimit_state, func);
}
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)
{
unsigned long elapsed = jiffies - *caller_jiffies;
if (*caller_jiffies && elapsed <= msecs_to_jiffies(interval_msecs))
return false;
*caller_jiffies = jiffies;
return true;
}
EXPORT_SYMBOL(printk_timed_ratelimit);
static DEFINE_SPINLOCK(dump_list_lock);
static LIST_HEAD(dump_list);
/**
* kmsg_dump_register - register a kernel log dumper.
* @dumper: pointer to the kmsg_dumper structure
*
* Adds a kernel log dumper to the system. The dump callback in the
* structure will be called when the kernel oopses or panics and must be
* set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
*/
int kmsg_dump_register(struct kmsg_dumper *dumper)
{
unsigned long flags;
int err = -EBUSY;
/* The dump callback needs to be set */
if (!dumper->dump)
return -EINVAL;
spin_lock_irqsave(&dump_list_lock, flags);
/* Don't allow registering multiple times */
if (!dumper->registered) {
dumper->registered = 1;
list_add_tail_rcu(&dumper->list, &dump_list);
err = 0;
}
spin_unlock_irqrestore(&dump_list_lock, flags);
return err;
}
EXPORT_SYMBOL_GPL(kmsg_dump_register);
/**
* kmsg_dump_unregister - unregister a kmsg dumper.
* @dumper: pointer to the kmsg_dumper structure
*
* Removes a dump device from the system. Returns zero on success and
* %-EINVAL otherwise.
*/
int kmsg_dump_unregister(struct kmsg_dumper *dumper)
{
unsigned long flags;
int err = -EINVAL;
spin_lock_irqsave(&dump_list_lock, flags);
if (dumper->registered) {
dumper->registered = 0;
list_del_rcu(&dumper->list);
err = 0;
}
spin_unlock_irqrestore(&dump_list_lock, flags);
synchronize_rcu();
return err;
}
EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
static bool always_kmsg_dump;
module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason)
{
switch (reason) {
case KMSG_DUMP_PANIC:
return "Panic";
case KMSG_DUMP_OOPS:
return "Oops";
case KMSG_DUMP_EMERG:
return "Emergency";
case KMSG_DUMP_SHUTDOWN:
return "Shutdown";
default:
return "Unknown";
}
}
EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
/**
* kmsg_dump - dump kernel log to kernel message dumpers.
* @reason: the reason (oops, panic etc) for dumping
*
* Call each of the registered dumper's dump() callback, which can
* retrieve the kmsg records with kmsg_dump_get_line() or
* kmsg_dump_get_buffer().
*/
void kmsg_dump(enum kmsg_dump_reason reason)
{
struct kmsg_dumper *dumper;
rcu_read_lock();
list_for_each_entry_rcu(dumper, &dump_list, list) {
enum kmsg_dump_reason max_reason = dumper->max_reason;
/*
* If client has not provided a specific max_reason, default
* to KMSG_DUMP_OOPS, unless always_kmsg_dump was set.
*/
if (max_reason == KMSG_DUMP_UNDEF) {
max_reason = always_kmsg_dump ? KMSG_DUMP_MAX :
KMSG_DUMP_OOPS;
}
if (reason > max_reason)
continue;
/* invoke dumper which will iterate over records */
dumper->dump(dumper, reason);
}
rcu_read_unlock();
}
/**
* kmsg_dump_get_line - retrieve one kmsg log line
* @iter: kmsg dump iterator
* @syslog: include the "<4>" prefixes
* @line: buffer to copy the line to
* @size: maximum size of the buffer
* @len: length of line placed into buffer
*
* Start at the beginning of the kmsg buffer, with the oldest kmsg
* record, and copy one record into the provided buffer.
*
* Consecutive calls will return the next available record moving
* towards the end of the buffer with the youngest messages.
*
* A return value of FALSE indicates that there are no more records to
* read.
*/
bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
char *line, size_t size, size_t *len)
{
u64 min_seq = latched_seq_read_nolock(&clear_seq);
struct printk_info info;
unsigned int line_count;
struct printk_record r;
unsigned long flags;
size_t l = 0;
bool ret = false;
if (iter->cur_seq < min_seq)
iter->cur_seq = min_seq;
printk_safe_enter_irqsave(flags);
prb_rec_init_rd(&r, &info, line, size);
/* Read text or count text lines? */
if (line) {
if (!prb_read_valid(prb, iter->cur_seq, &r))
goto out;
l = record_print_text(&r, syslog, printk_time);
} else {
if (!prb_read_valid_info(prb, iter->cur_seq,
&info, &line_count)) {
goto out;
}
l = get_record_print_text_size(&info, line_count, syslog,
printk_time);
}
iter->cur_seq = r.info->seq + 1;
ret = true;
out:
printk_safe_exit_irqrestore(flags);
if (len)
*len = l;
return ret;
}
EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
/**
* kmsg_dump_get_buffer - copy kmsg log lines
* @iter: kmsg dump iterator
* @syslog: include the "<4>" prefixes
* @buf: buffer to copy the line to
* @size: maximum size of the buffer
* @len_out: length of line placed into buffer
*
* Start at the end of the kmsg buffer and fill the provided buffer
* with as many of the *youngest* kmsg records that fit into it.
* If the buffer is large enough, all available kmsg records will be
* copied with a single call.
*
* Consecutive calls will fill the buffer with the next block of
* available older records, not including the earlier retrieved ones.
*
* A return value of FALSE indicates that there are no more records to
* read.
*/
bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
char *buf, size_t size, size_t *len_out)
{
u64 min_seq = latched_seq_read_nolock(&clear_seq);
struct printk_info info;
struct printk_record r;
unsigned long flags;
u64 seq;
u64 next_seq;
size_t len = 0;
bool ret = false;
bool time = printk_time;
if (!buf || !size)
goto out;
if (iter->cur_seq < min_seq)
iter->cur_seq = min_seq;
printk_safe_enter_irqsave(flags);
if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
if (info.seq != iter->cur_seq) {
/* messages are gone, move to first available one */
iter->cur_seq = info.seq;
}
}
/* last entry */
if (iter->cur_seq >= iter->next_seq) {
printk_safe_exit_irqrestore(flags);
goto out;
}
/*
* Find first record that fits, including all following records,
* into the user-provided buffer for this dump. Pass in size-1
* because this function (by way of record_print_text()) will
* not write more than size-1 bytes of text into @buf.
*/
seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
size - 1, syslog, time);
/*
* Next kmsg_dump_get_buffer() invocation will dump block of
* older records stored right before this one.
*/
next_seq = seq;
prb_rec_init_rd(&r, &info, buf, size);
len = 0;
prb_for_each_record(seq, prb, seq, &r) {
if (r.info->seq >= iter->next_seq)
break;
len += record_print_text(&r, syslog, time);
/* Adjust record to store to remaining buffer space. */
prb_rec_init_rd(&r, &info, buf + len, size - len);
}
iter->next_seq = next_seq;
ret = true;
printk_safe_exit_irqrestore(flags);
out:
if (len_out)
*len_out = len;
return ret;
}
EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
/**
* kmsg_dump_rewind - reset the iterator
* @iter: kmsg dump iterator
*
* Reset the dumper's iterator so that kmsg_dump_get_line() and
* kmsg_dump_get_buffer() can be called again and used multiple
* times within the same dumper.dump() callback.
*/
void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
{
unsigned long flags;
printk_safe_enter_irqsave(flags);
iter->cur_seq = latched_seq_read_nolock(&clear_seq);
iter->next_seq = prb_next_seq(prb);
printk_safe_exit_irqrestore(flags);
}
EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
#endif
#ifdef CONFIG_SMP
static atomic_t printk_cpulock_owner = ATOMIC_INIT(-1);
static atomic_t printk_cpulock_nested = ATOMIC_INIT(0);
/**
* __printk_wait_on_cpu_lock() - Busy wait until the printk cpu-reentrant
* spinning lock is not owned by any CPU.
*
* Context: Any context.
*/
void __printk_wait_on_cpu_lock(void)
{
do {
cpu_relax();
} while (atomic_read(&printk_cpulock_owner) != -1);
}
EXPORT_SYMBOL(__printk_wait_on_cpu_lock);
/**
* __printk_cpu_trylock() - Try to acquire the printk cpu-reentrant
* spinning lock.
*
* If no processor has the lock, the calling processor takes the lock and
* becomes the owner. If the calling processor is already the owner of the
* lock, this function succeeds immediately.
*
* Context: Any context. Expects interrupts to be disabled.
* Return: 1 on success, otherwise 0.
*/
int __printk_cpu_trylock(void)
{
int cpu;
int old;
cpu = smp_processor_id();
/*
* Guarantee loads and stores from this CPU when it is the lock owner
* are _not_ visible to the previous lock owner. This pairs with
* __printk_cpu_unlock:B.
*
* Memory barrier involvement:
*
* If __printk_cpu_trylock:A reads from __printk_cpu_unlock:B, then
* __printk_cpu_unlock:A can never read from __printk_cpu_trylock:B.
*
* Relies on:
*
* RELEASE from __printk_cpu_unlock:A to __printk_cpu_unlock:B
* of the previous CPU
* matching
* ACQUIRE from __printk_cpu_trylock:A to __printk_cpu_trylock:B
* of this CPU
*/
old = atomic_cmpxchg_acquire(&printk_cpulock_owner, -1,
cpu); /* LMM(__printk_cpu_trylock:A) */
if (old == -1) {
/*
* This CPU is now the owner and begins loading/storing
* data: LMM(__printk_cpu_trylock:B)
*/
return 1;
} else if (old == cpu) {
/* This CPU is already the owner. */
atomic_inc(&printk_cpulock_nested);
return 1;
}
return 0;
}
EXPORT_SYMBOL(__printk_cpu_trylock);
/**
* __printk_cpu_unlock() - Release the printk cpu-reentrant spinning lock.
*
* The calling processor must be the owner of the lock.
*
* Context: Any context. Expects interrupts to be disabled.
*/
void __printk_cpu_unlock(void)
{
if (atomic_read(&printk_cpulock_nested)) {
atomic_dec(&printk_cpulock_nested);
return;
}
/*
* This CPU is finished loading/storing data:
* LMM(__printk_cpu_unlock:A)
*/
/*
* Guarantee loads and stores from this CPU when it was the
* lock owner are visible to the next lock owner. This pairs
* with __printk_cpu_trylock:A.
*
* Memory barrier involvement:
*
* If __printk_cpu_trylock:A reads from __printk_cpu_unlock:B,
* then __printk_cpu_trylock:B reads from __printk_cpu_unlock:A.
*
* Relies on:
*
* RELEASE from __printk_cpu_unlock:A to __printk_cpu_unlock:B
* of this CPU
* matching
* ACQUIRE from __printk_cpu_trylock:A to __printk_cpu_trylock:B
* of the next CPU
*/
atomic_set_release(&printk_cpulock_owner,
-1); /* LMM(__printk_cpu_unlock:B) */
}
EXPORT_SYMBOL(__printk_cpu_unlock);
#endif /* CONFIG_SMP */