kernel/printk.c

   1 /*
   2  *  linux/kernel/printk.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  *
   6  * Modified to make sys_syslog() more flexible: added commands to
   7  * return the last 4k of kernel messages, regardless of whether
   8  * they've been read or not.  Added option to suppress kernel printk's
   9  * to the console.  Added hook for sending the console messages
  10  * elsewhere, in preparation for a serial line console (someday).
  11  * Ted Ts'o, 2/11/93.
  12  * Modified for sysctl support, 1/8/97, Chris Horn.
  13  * Fixed SMP synchronization, 08/08/99, Manfred Spraul
  14  *     manfred@colorfullife.com
  15  * Rewrote bits to get rid of console_lock
  16  *      01Mar01 Andrew Morton
  17  */
  18
  19 #include <linux/kernel.h>
  20 #include <linux/mm.h>
  21 #include <linux/tty.h>
  22 #include <linux/tty_driver.h>
  23 #include <linux/console.h>
  24 #include <linux/init.h>
  25 #include <linux/jiffies.h>
  26 #include <linux/nmi.h>
  27 #include <linux/module.h>
  28 #include <linux/moduleparam.h>
  29 #include <linux/interrupt.h>                    /* For in_interrupt() */
  30 #include <linux/delay.h>
  31 #include <linux/smp.h>
  32 #include <linux/security.h>
  33 #include <linux/bootmem.h>
  34 #include <linux/syscalls.h>
  35 #include <linux/kexec.h>
  36
  37 #include <asm/uaccess.h>
  38
  39 /*
  40  * for_each_console() allows you to iterate on each console
  41  */
  42 #define for_each_console(con) \
  43         for (con = console_drivers; con != NULL; con = con->next)
  44
  45 /*
  46  * Architectures can override it:
  47  */
  48 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
  49 {
  50 }
  51
  52 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  53
  54 /* printk's without a loglevel use this.. */
  55 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  56
  57 /* We show everything that is MORE important than this.. */
  58 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  59 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  60
  61 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  62
  63 int console_printk[4] = {
  64         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  65         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  66         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  67         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  68 };
  69
  70 static int saved_console_loglevel = -1;
  71
  72 /*
  73  * Low level drivers may need that to know if they can schedule in
  74  * their unblank() callback or not. So let's export it.
  75  */
  76 int oops_in_progress;
  77 EXPORT_SYMBOL(oops_in_progress);
  78
  79 /*
  80  * console_sem protects the console_drivers list, and also
  81  * provides serialisation for access to the entire console
  82  * driver system.
  83  */
  84 static DECLARE_MUTEX(console_sem);
  85 struct console *console_drivers;
  86 EXPORT_SYMBOL_GPL(console_drivers);
  87
  88 /*
  89  * This is used for debugging the mess that is the VT code by
  90  * keeping track if we have the console semaphore held. It's
  91  * definitely not the perfect debug tool (we don't know if _WE_
  92  * hold it are racing, but it helps tracking those weird code
  93  * path in the console code where we end up in places I want
  94  * locked without the console sempahore held
  95  */
  96 static int console_locked, console_suspended;
  97
  98 /*
  99  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
 100  * It is also used in interesting ways to provide interlocking in
 101  * release_console_sem().
 102  */
 103 static DEFINE_SPINLOCK(logbuf_lock);
 104
 105 #define LOG_BUF_MASK (log_buf_len-1)
 106 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
 107
 108 /*
 109  * The indices into log_buf are not constrained to log_buf_len - they
 110  * must be masked before subscripting
 111  */
 112 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
 113 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
 114 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
 115
 116 /*
 117  *      Array of consoles built from command line options (console=)
 118  */
 119 struct console_cmdline
 120 {
 121         char    name[8];                        /* Name of the driver       */
 122         int     index;                          /* Minor dev. to use        */
 123         char    *options;                       /* Options for the driver   */
 124 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 125         char    *brl_options;                   /* Options for braille driver */
 126 #endif
 127 };
 128
 129 #define MAX_CMDLINECONSOLES 8
 130
 131 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 132 static int selected_console = -1;
 133 static int preferred_console = -1;
 134 int console_set_on_cmdline;
 135 EXPORT_SYMBOL(console_set_on_cmdline);
 136
 137 /* Flag: console code may call schedule() */
 138 static int console_may_schedule;
 139
 140 #ifdef CONFIG_PRINTK
 141
 142 static char __log_buf[__LOG_BUF_LEN];
 143 static char *log_buf = __log_buf;
 144 static int log_buf_len = __LOG_BUF_LEN;
 145 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
 146
 147 #ifdef CONFIG_KEXEC
 148 /*
 149  * This appends the listed symbols to /proc/vmcoreinfo
 150  *
 151  * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
 152  * obtain access to symbols that are otherwise very difficult to locate.  These
 153  * symbols are specifically used so that utilities can access and extract the
 154  * dmesg log from a vmcore file after a crash.
 155  */
 156 void log_buf_kexec_setup(void)
 157 {
 158         VMCOREINFO_SYMBOL(log_buf);
 159         VMCOREINFO_SYMBOL(log_end);
 160         VMCOREINFO_SYMBOL(log_buf_len);
 161         VMCOREINFO_SYMBOL(logged_chars);
 162 }
 163 #endif
 164
 165 static int __init log_buf_len_setup(char *str)
 166 {
 167         unsigned size = memparse(str, &str);
 168         unsigned long flags;
 169
 170         if (size)
 171                 size = roundup_pow_of_two(size);
 172         if (size > log_buf_len) {
 173                 unsigned start, dest_idx, offset;
 174                 char *new_log_buf;
 175
 176                 new_log_buf = alloc_bootmem(size);
 177                 if (!new_log_buf) {
 178                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 179                         goto out;
 180                 }
 181
 182                 spin_lock_irqsave(&logbuf_lock, flags);
 183                 log_buf_len = size;
 184                 log_buf = new_log_buf;
 185
 186                 offset = start = min(con_start, log_start);
 187                 dest_idx = 0;
 188                 while (start != log_end) {
 189                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 190                         start++;
 191                         dest_idx++;
 192                 }
 193                 log_start -= offset;
 194                 con_start -= offset;
 195                 log_end -= offset;
 196                 spin_unlock_irqrestore(&logbuf_lock, flags);
 197
 198                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 199         }
 200 out:
 201         return 1;
 202 }
 203
 204 __setup("log_buf_len=", log_buf_len_setup);
 205
 206 #ifdef CONFIG_BOOT_PRINTK_DELAY
 207
 208 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
 209 static unsigned long long loops_per_msec;       /* based on boot_delay */
 210
 211 static int __init boot_delay_setup(char *str)
 212 {
 213         unsigned long lpj;
 214
 215         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
 216         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 217
 218         get_option(&str, &boot_delay);
 219         if (boot_delay > 10 * 1000)
 220                 boot_delay = 0;
 221
 222         pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
 223                 "HZ: %d, loops_per_msec: %llu\n",
 224                 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
 225         return 1;
 226 }
 227 __setup("boot_delay=", boot_delay_setup);
 228
 229 static void boot_delay_msec(void)
 230 {
 231         unsigned long long k;
 232         unsigned long timeout;
 233
 234         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
 235                 return;
 236
 237         k = (unsigned long long)loops_per_msec * boot_delay;
 238
 239         timeout = jiffies + msecs_to_jiffies(boot_delay);
 240         while (k) {
 241                 k--;
 242                 cpu_relax();
 243                 /*
 244                  * use (volatile) jiffies to prevent
 245                  * compiler reduction; loop termination via jiffies
 246                  * is secondary and may or may not happen.
 247                  */
 248                 if (time_after(jiffies, timeout))
 249                         break;
 250                 touch_nmi_watchdog();
 251         }
 252 }
 253 #else
 254 static inline void boot_delay_msec(void)
 255 {
 256 }
 257 #endif
 258
 259 /*
 260  * Commands to do_syslog:
 261  *
 262  *      0 -- Close the log.  Currently a NOP.
 263  *      1 -- Open the log. Currently a NOP.
 264  *      2 -- Read from the log.
 265  *      3 -- Read all messages remaining in the ring buffer.
 266  *      4 -- Read and clear all messages remaining in the ring buffer
 267  *      5 -- Clear ring buffer.
 268  *      6 -- Disable printk's to console
 269  *      7 -- Enable printk's to console
 270  *      8 -- Set level of messages printed to console
 271  *      9 -- Return number of unread characters in the log buffer
 272  *     10 -- Return size of the log buffer
 273  */
 274 int do_syslog(int type, char __user *buf, int len)
 275 {
 276         unsigned i, j, limit, count;
 277         int do_clear = 0;
 278         char c;
 279         int error = 0;
 280
 281         error = security_syslog(type);
 282         if (error)
 283                 return error;
 284
 285         switch (type) {
 286         case 0:         /* Close log */
 287                 break;
 288         case 1:         /* Open log */
 289                 break;
 290         case 2:         /* Read from log */
 291                 error = -EINVAL;
 292                 if (!buf || len < 0)
 293                         goto out;
 294                 error = 0;
 295                 if (!len)
 296                         goto out;
 297                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 298                         error = -EFAULT;
 299                         goto out;
 300                 }
 301                 error = wait_event_interruptible(log_wait,
 302                                                         (log_start - log_end));
 303                 if (error)
 304                         goto out;
 305                 i = 0;
 306                 spin_lock_irq(&logbuf_lock);
 307                 while (!error && (log_start != log_end) && i < len) {
 308                         c = LOG_BUF(log_start);
 309                         log_start++;
 310                         spin_unlock_irq(&logbuf_lock);
 311                         error = __put_user(c,buf);
 312                         buf++;
 313                         i++;
 314                         cond_resched();
 315                         spin_lock_irq(&logbuf_lock);
 316                 }
 317                 spin_unlock_irq(&logbuf_lock);
 318                 if (!error)
 319                         error = i;
 320                 break;
 321         case 4:         /* Read/clear last kernel messages */
 322                 do_clear = 1;
 323                 /* FALL THRU */
 324         case 3:         /* Read last kernel messages */
 325                 error = -EINVAL;
 326                 if (!buf || len < 0)
 327                         goto out;
 328                 error = 0;
 329                 if (!len)
 330                         goto out;
 331                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 332                         error = -EFAULT;
 333                         goto out;
 334                 }
 335                 count = len;
 336                 if (count > log_buf_len)
 337                         count = log_buf_len;
 338                 spin_lock_irq(&logbuf_lock);
 339                 if (count > logged_chars)
 340                         count = logged_chars;
 341                 if (do_clear)
 342                         logged_chars = 0;
 343                 limit = log_end;
 344                 /*
 345                  * __put_user() could sleep, and while we sleep
 346                  * printk() could overwrite the messages
 347                  * we try to copy to user space. Therefore
 348                  * the messages are copied in reverse. <manfreds>
 349                  */
 350                 for (i = 0; i < count && !error; i++) {
 351                         j = limit-1-i;
 352                         if (j + log_buf_len < log_end)
 353                                 break;
 354                         c = LOG_BUF(j);
 355                         spin_unlock_irq(&logbuf_lock);
 356                         error = __put_user(c,&buf[count-1-i]);
 357                         cond_resched();
 358                         spin_lock_irq(&logbuf_lock);
 359                 }
 360                 spin_unlock_irq(&logbuf_lock);
 361                 if (error)
 362                         break;
 363                 error = i;
 364                 if (i != count) {
 365                         int offset = count-error;
 366                         /* buffer overflow during copy, correct user buffer. */
 367                         for (i = 0; i < error; i++) {
 368                                 if (__get_user(c,&buf[i+offset]) ||
 369                                     __put_user(c,&buf[i])) {
 370                                         error = -EFAULT;
 371                                         break;
 372                                 }
 373                                 cond_resched();
 374                         }
 375                 }
 376                 break;
 377         case 5:         /* Clear ring buffer */
 378                 logged_chars = 0;
 379                 break;
 380         case 6:         /* Disable logging to console */
 381                 if (saved_console_loglevel == -1)
 382                         saved_console_loglevel = console_loglevel;
 383                 console_loglevel = minimum_console_loglevel;
 384                 break;
 385         case 7:         /* Enable logging to console */
 386                 if (saved_console_loglevel != -1) {
 387                         console_loglevel = saved_console_loglevel;
 388                         saved_console_loglevel = -1;
 389                 }
 390                 break;
 391         case 8:         /* Set level of messages printed to console */
 392                 error = -EINVAL;
 393                 if (len < 1 || len > 8)
 394                         goto out;
 395                 if (len < minimum_console_loglevel)
 396                         len = minimum_console_loglevel;
 397                 console_loglevel = len;
 398                 /* Implicitly re-enable logging to console */
 399                 saved_console_loglevel = -1;
 400                 error = 0;
 401                 break;
 402         case 9:         /* Number of chars in the log buffer */
 403                 error = log_end - log_start;
 404                 break;
 405         case 10:        /* Size of the log buffer */
 406                 error = log_buf_len;
 407                 break;
 408         default:
 409                 error = -EINVAL;
 410                 break;
 411         }
 412 out:
 413         return error;
 414 }
 415
 416 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
 417 {
 418         return do_syslog(type, buf, len);
 419 }
 420
 421 /*
 422  * Call the console drivers on a range of log_buf
 423  */
 424 static void __call_console_drivers(unsigned start, unsigned end)
 425 {
 426         struct console *con;
 427
 428         for_each_console(con) {
 429                 if ((con->flags & CON_ENABLED) && con->write &&
 430                                 (cpu_online(smp_processor_id()) ||
 431                                 (con->flags & CON_ANYTIME)))
 432                         con->write(con, &LOG_BUF(start), end - start);
 433         }
 434 }
 435
 436 static int __read_mostly ignore_loglevel;
 437
 438 static int __init ignore_loglevel_setup(char *str)
 439 {
 440         ignore_loglevel = 1;
 441         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 442
 443         return 0;
 444 }
 445
 446 early_param("ignore_loglevel", ignore_loglevel_setup);
 447
 448 /*
 449  * Write out chars from start to end - 1 inclusive
 450  */
 451 static void _call_console_drivers(unsigned start,
 452                                 unsigned end, int msg_log_level)
 453 {
 454         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 455                         console_drivers && start != end) {
 456                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 457                         /* wrapped write */
 458                         __call_console_drivers(start & LOG_BUF_MASK,
 459                                                 log_buf_len);
 460                         __call_console_drivers(0, end & LOG_BUF_MASK);
 461                 } else {
 462                         __call_console_drivers(start, end);
 463                 }
 464         }
 465 }
 466
 467 /*
 468  * Call the console drivers, asking them to write out
 469  * log_buf[start] to log_buf[end - 1].
 470  * The console_sem must be held.
 471  */
 472 static void call_console_drivers(unsigned start, unsigned end)
 473 {
 474         unsigned cur_index, start_print;
 475         static int msg_level = -1;
 476
 477         BUG_ON(((int)(start - end)) > 0);
 478
 479         cur_index = start;
 480         start_print = start;
 481         while (cur_index != end) {
 482                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 483                                 LOG_BUF(cur_index + 0) == '<' &&
 484                                 LOG_BUF(cur_index + 1) >= '0' &&
 485                                 LOG_BUF(cur_index + 1) <= '7' &&
 486                                 LOG_BUF(cur_index + 2) == '>') {
 487                         msg_level = LOG_BUF(cur_index + 1) - '0';
 488                         cur_index += 3;
 489                         start_print = cur_index;
 490                 }
 491                 while (cur_index != end) {
 492                         char c = LOG_BUF(cur_index);
 493
 494                         cur_index++;
 495                         if (c == '\n') {
 496                                 if (msg_level < 0) {
 497                                         /*
 498                                          * printk() has already given us loglevel tags in
 499                                          * the buffer.  This code is here in case the
 500                                          * log buffer has wrapped right round and scribbled
 501                                          * on those tags
 502                                          */
 503                                         msg_level = default_message_loglevel;
 504                                 }
 505                                 _call_console_drivers(start_print, cur_index, msg_level);
 506                                 msg_level = -1;
 507                                 start_print = cur_index;
 508                                 break;
 509                         }
 510                 }
 511         }
 512         _call_console_drivers(start_print, end, msg_level);
 513 }
 514
 515 static void emit_log_char(char c)
 516 {
 517         LOG_BUF(log_end) = c;
 518         log_end++;
 519         if (log_end - log_start > log_buf_len)
 520                 log_start = log_end - log_buf_len;
 521         if (log_end - con_start > log_buf_len)
 522                 con_start = log_end - log_buf_len;
 523         if (logged_chars < log_buf_len)
 524                 logged_chars++;
 525 }
 526
 527 /*
 528  * Zap console related locks when oopsing. Only zap at most once
 529  * every 10 seconds, to leave time for slow consoles to print a
 530  * full oops.
 531  */
 532 static void zap_locks(void)
 533 {
 534         static unsigned long oops_timestamp;
 535
 536         if (time_after_eq(jiffies, oops_timestamp) &&
 537                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 538                 return;
 539
 540         oops_timestamp = jiffies;
 541
 542         /* If a crash is occurring, make sure we can't deadlock */
 543         spin_lock_init(&logbuf_lock);
 544         /* And make sure that we print immediately */
 545         init_MUTEX(&console_sem);
 546 }
 547
 548 #if defined(CONFIG_PRINTK_TIME)
 549 static int printk_time = 1;
 550 #else
 551 static int printk_time = 0;
 552 #endif
 553 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 554
 555 /* Check if we have any console registered that can be called early in boot. */
 556 static int have_callable_console(void)
 557 {
 558         struct console *con;
 559
 560         for_each_console(con)
 561                 if (con->flags & CON_ANYTIME)
 562                         return 1;
 563
 564         return 0;
 565 }
 566
 567 /**
 568  * printk - print a kernel message
 569  * @fmt: format string
 570  *
 571  * This is printk().  It can be called from any context.  We want it to work.
 572  *
 573  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 574  * call the console drivers.  If we fail to get the semaphore we place the output
 575  * into the log buffer and return.  The current holder of the console_sem will
 576  * notice the new output in release_console_sem() and will send it to the
 577  * consoles before releasing the semaphore.
 578  *
 579  * One effect of this deferred printing is that code which calls printk() and
 580  * then changes console_loglevel may break. This is because console_loglevel
 581  * is inspected when the actual printing occurs.
 582  *
 583  * See also:
 584  * printf(3)
 585  *
 586  * See the vsnprintf() documentation for format string extensions over C99.
 587  */
 588
 589 asmlinkage int printk(const char *fmt, ...)
 590 {
 591         va_list args;
 592         int r;
 593
 594         va_start(args, fmt);
 595         r = vprintk(fmt, args);
 596         va_end(args);
 597
 598         return r;
 599 }
 600
 601 /* cpu currently holding logbuf_lock */
 602 static volatile unsigned int printk_cpu = UINT_MAX;
 603
 604 /*
 605  * Can we actually use the console at this time on this cpu?
 606  *
 607  * Console drivers may assume that per-cpu resources have
 608  * been allocated. So unless they're explicitly marked as
 609  * being able to cope (CON_ANYTIME) don't call them until
 610  * this CPU is officially up.
 611  */
 612 static inline int can_use_console(unsigned int cpu)
 613 {
 614         return cpu_online(cpu) || have_callable_console();
 615 }
 616
 617 /*
 618  * Try to get console ownership to actually show the kernel
 619  * messages from a 'printk'. Return true (and with the
 620  * console_semaphore held, and 'console_locked' set) if it
 621  * is successful, false otherwise.
 622  *
 623  * This gets called with the 'logbuf_lock' spinlock held and
 624  * interrupts disabled. It should return with 'lockbuf_lock'
 625  * released but interrupts still disabled.
 626  */
 627 static int acquire_console_semaphore_for_printk(unsigned int cpu)
 628 {
 629         int retval = 0;
 630
 631         if (!try_acquire_console_sem()) {
 632                 retval = 1;
 633
 634                 /*
 635                  * If we can't use the console, we need to release
 636                  * the console semaphore by hand to avoid flushing
 637                  * the buffer. We need to hold the console semaphore
 638                  * in order to do this test safely.
 639                  */
 640                 if (!can_use_console(cpu)) {
 641                         console_locked = 0;
 642                         up(&console_sem);
 643                         retval = 0;
 644                 }
 645         }
 646         printk_cpu = UINT_MAX;
 647         spin_unlock(&logbuf_lock);
 648         return retval;
 649 }
 650 static const char recursion_bug_msg [] =
 651                 KERN_CRIT "BUG: recent printk recursion!\n";
 652 static int recursion_bug;
 653 static int new_text_line = 1;
 654 static char printk_buf[1024];
 655
 656 int printk_delay_msec __read_mostly;
 657
 658 static inline void printk_delay(void)
 659 {
 660         if (unlikely(printk_delay_msec)) {
 661                 int m = printk_delay_msec;
 662
 663                 while (m--) {
 664                         mdelay(1);
 665                         touch_nmi_watchdog();
 666                 }
 667         }
 668 }
 669
 670 asmlinkage int vprintk(const char *fmt, va_list args)
 671 {
 672         int printed_len = 0;
 673         int current_log_level = default_message_loglevel;
 674         unsigned long flags;
 675         int this_cpu;
 676         char *p;
 677
 678         boot_delay_msec();
 679         printk_delay();
 680
 681         preempt_disable();
 682         /* This stops the holder of console_sem just where we want him */
 683         raw_local_irq_save(flags);
 684         this_cpu = smp_processor_id();
 685
 686         /*
 687          * Ouch, printk recursed into itself!
 688          */
 689         if (unlikely(printk_cpu == this_cpu)) {
 690                 /*
 691                  * If a crash is occurring during printk() on this CPU,
 692                  * then try to get the crash message out but make sure
 693                  * we can't deadlock. Otherwise just return to avoid the
 694                  * recursion and return - but flag the recursion so that
 695                  * it can be printed at the next appropriate moment:
 696                  */
 697                 if (!oops_in_progress) {
 698                         recursion_bug = 1;
 699                         goto out_restore_irqs;
 700                 }
 701                 zap_locks();
 702         }
 703
 704         lockdep_off();
 705         spin_lock(&logbuf_lock);
 706         printk_cpu = this_cpu;
 707
 708         if (recursion_bug) {
 709                 recursion_bug = 0;
 710                 strcpy(printk_buf, recursion_bug_msg);
 711                 printed_len = strlen(recursion_bug_msg);
 712         }
 713         /* Emit the output into the temporary buffer */
 714         printed_len += vscnprintf(printk_buf + printed_len,
 715                                   sizeof(printk_buf) - printed_len, fmt, args);
 716
 717
 718         p = printk_buf;
 719
 720         /* Do we have a loglevel in the string? */
 721         if (p[0] == '<') {
 722                 unsigned char c = p[1];
 723                 if (c && p[2] == '>') {
 724                         switch (c) {
 725                         case '0' ... '7': /* loglevel */
 726                                 current_log_level = c - '0';
 727                         /* Fallthrough - make sure we're on a new line */
 728                         case 'd': /* KERN_DEFAULT */
 729                                 if (!new_text_line) {
 730                                         emit_log_char('\n');
 731                                         new_text_line = 1;
 732                                 }
 733                         /* Fallthrough - skip the loglevel */
 734                         case 'c': /* KERN_CONT */
 735                                 p += 3;
 736                                 break;
 737                         }
 738                 }
 739         }
 740
 741         /*
 742          * Copy the output into log_buf.  If the caller didn't provide
 743          * appropriate log level tags, we insert them here
 744          */
 745         for ( ; *p; p++) {
 746                 if (new_text_line) {
 747                         /* Always output the token */
 748                         emit_log_char('<');
 749                         emit_log_char(current_log_level + '0');
 750                         emit_log_char('>');
 751                         printed_len += 3;
 752                         new_text_line = 0;
 753
 754                         if (printk_time) {
 755                                 /* Follow the token with the time */
 756                                 char tbuf[50], *tp;
 757                                 unsigned tlen;
 758                                 unsigned long long t;
 759                                 unsigned long nanosec_rem;
 760
 761                                 t = cpu_clock(printk_cpu);
 762                                 nanosec_rem = do_div(t, 1000000000);
 763                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
 764                                                 (unsigned long) t,
 765                                                 nanosec_rem / 1000);
 766
 767                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 768                                         emit_log_char(*tp);
 769                                 printed_len += tlen;
 770                         }
 771
 772                         if (!*p)
 773                                 break;
 774                 }
 775
 776                 emit_log_char(*p);
 777                 if (*p == '\n')
 778                         new_text_line = 1;
 779         }
 780
 781         /*
 782          * Try to acquire and then immediately release the
 783          * console semaphore. The release will do all the
 784          * actual magic (print out buffers, wake up klogd,
 785          * etc).
 786          *
 787          * The acquire_console_semaphore_for_printk() function
 788          * will release 'logbuf_lock' regardless of whether it
 789          * actually gets the semaphore or not.
 790          */
 791         if (acquire_console_semaphore_for_printk(this_cpu))
 792                 release_console_sem();
 793
 794         lockdep_on();
 795 out_restore_irqs:
 796         raw_local_irq_restore(flags);
 797
 798         preempt_enable();
 799         return printed_len;
 800 }
 801 EXPORT_SYMBOL(printk);
 802 EXPORT_SYMBOL(vprintk);
 803
 804 #else
 805
 806 static void call_console_drivers(unsigned start, unsigned end)
 807 {
 808 }
 809
 810 #endif
 811
 812 static int __add_preferred_console(char *name, int idx, char *options,
 813                                    char *brl_options)
 814 {
 815         struct console_cmdline *c;
 816         int i;
 817
 818         /*
 819          *      See if this tty is not yet registered, and
 820          *      if we have a slot free.
 821          */
 822         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 823                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 824                           console_cmdline[i].index == idx) {
 825                                 if (!brl_options)
 826                                         selected_console = i;
 827                                 return 0;
 828                 }
 829         if (i == MAX_CMDLINECONSOLES)
 830                 return -E2BIG;
 831         if (!brl_options)
 832                 selected_console = i;
 833         c = &console_cmdline[i];
 834         strlcpy(c->name, name, sizeof(c->name));
 835         c->options = options;
 836 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 837         c->brl_options = brl_options;
 838 #endif
 839         c->index = idx;
 840         return 0;
 841 }
 842 /*
 843  * Set up a list of consoles.  Called from init/main.c
 844  */
 845 static int __init console_setup(char *str)
 846 {
 847         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 848         char *s, *options, *brl_options = NULL;
 849         int idx;
 850
 851 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 852         if (!memcmp(str, "brl,", 4)) {
 853                 brl_options = "";
 854                 str += 4;
 855         } else if (!memcmp(str, "brl=", 4)) {
 856                 brl_options = str + 4;
 857                 str = strchr(brl_options, ',');
 858                 if (!str) {
 859                         printk(KERN_ERR "need port name after brl=\n");
 860                         return 1;
 861                 }
 862                 *(str++) = 0;
 863         }
 864 #endif
 865
 866         /*
 867          * Decode str into name, index, options.
 868          */
 869         if (str[0] >= '0' && str[0] <= '9') {
 870                 strcpy(buf, "ttyS");
 871                 strncpy(buf + 4, str, sizeof(buf) - 5);
 872         } else {
 873                 strncpy(buf, str, sizeof(buf) - 1);
 874         }
 875         buf[sizeof(buf) - 1] = 0;
 876         if ((options = strchr(str, ',')) != NULL)
 877                 *(options++) = 0;
 878 #ifdef __sparc__
 879         if (!strcmp(str, "ttya"))
 880                 strcpy(buf, "ttyS0");
 881         if (!strcmp(str, "ttyb"))
 882                 strcpy(buf, "ttyS1");
 883 #endif
 884         for (s = buf; *s; s++)
 885                 if ((*s >= '0' && *s <= '9') || *s == ',')
 886                         break;
 887         idx = simple_strtoul(s, NULL, 10);
 888         *s = 0;
 889
 890         __add_preferred_console(buf, idx, options, brl_options);
 891         console_set_on_cmdline = 1;
 892         return 1;
 893 }
 894 __setup("console=", console_setup);
 895
 896 /**
 897  * add_preferred_console - add a device to the list of preferred consoles.
 898  * @name: device name
 899  * @idx: device index
 900  * @options: options for this console
 901  *
 902  * The last preferred console added will be used for kernel messages
 903  * and stdin/out/err for init.  Normally this is used by console_setup
 904  * above to handle user-supplied console arguments; however it can also
 905  * be used by arch-specific code either to override the user or more
 906  * commonly to provide a default console (ie from PROM variables) when
 907  * the user has not supplied one.
 908  */
 909 int add_preferred_console(char *name, int idx, char *options)
 910 {
 911         return __add_preferred_console(name, idx, options, NULL);
 912 }
 913
 914 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 915 {
 916         struct console_cmdline *c;
 917         int i;
 918
 919         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 920                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 921                           console_cmdline[i].index == idx) {
 922                                 c = &console_cmdline[i];
 923                                 strlcpy(c->name, name_new, sizeof(c->name));
 924                                 c->name[sizeof(c->name) - 1] = 0;
 925                                 c->options = options;
 926                                 c->index = idx_new;
 927                                 return i;
 928                 }
 929         /* not found */
 930         return -1;
 931 }
 932
 933 int console_suspend_enabled = 1;
 934 EXPORT_SYMBOL(console_suspend_enabled);
 935
 936 static int __init console_suspend_disable(char *str)
 937 {
 938         console_suspend_enabled = 0;
 939         return 1;
 940 }
 941 __setup("no_console_suspend", console_suspend_disable);
 942
 943 /**
 944  * suspend_console - suspend the console subsystem
 945  *
 946  * This disables printk() while we go into suspend states
 947  */
 948 void suspend_console(void)
 949 {
 950         if (!console_suspend_enabled)
 951                 return;
 952         printk("Suspending console(s) (use no_console_suspend to debug)\n");
 953         acquire_console_sem();
 954         console_suspended = 1;
 955         up(&console_sem);
 956 }
 957
 958 void resume_console(void)
 959 {
 960         if (!console_suspend_enabled)
 961                 return;
 962         down(&console_sem);
 963         console_suspended = 0;
 964         release_console_sem();
 965 }
 966
 967 /**
 968  * acquire_console_sem - lock the console system for exclusive use.
 969  *
 970  * Acquires a semaphore which guarantees that the caller has
 971  * exclusive access to the console system and the console_drivers list.
 972  *
 973  * Can sleep, returns nothing.
 974  */
 975 void acquire_console_sem(void)
 976 {
 977         BUG_ON(in_interrupt());
 978         down(&console_sem);
 979         if (console_suspended)
 980                 return;
 981         console_locked = 1;
 982         console_may_schedule = 1;
 983 }
 984 EXPORT_SYMBOL(acquire_console_sem);
 985
 986 int try_acquire_console_sem(void)
 987 {
 988         if (down_trylock(&console_sem))
 989                 return -1;
 990         if (console_suspended) {
 991                 up(&console_sem);
 992                 return -1;
 993         }
 994         console_locked = 1;
 995         console_may_schedule = 0;
 996         return 0;
 997 }
 998 EXPORT_SYMBOL(try_acquire_console_sem);
 999
1000 int is_console_locked(void)
1001 {
1002         return console_locked;
1003 }
1004
1005 static DEFINE_PER_CPU(int, printk_pending);
1006
1007 void printk_tick(void)
1008 {
1009         if (__get_cpu_var(printk_pending)) {
1010                 __get_cpu_var(printk_pending) = 0;
1011                 wake_up_interruptible(&log_wait);
1012         }
1013 }
1014
1015 int printk_needs_cpu(int cpu)
1016 {
1017         if (unlikely(cpu_is_offline(cpu)))
1018                 printk_tick();
1019         return per_cpu(printk_pending, cpu);
1020 }
1021
1022 void wake_up_klogd(void)
1023 {
1024         if (waitqueue_active(&log_wait))
1025                 __raw_get_cpu_var(printk_pending) = 1;
1026 }
1027
1028 /**
1029  * release_console_sem - unlock the console system
1030  *
1031  * Releases the semaphore which the caller holds on the console system
1032  * and the console driver list.
1033  *
1034  * While the semaphore was held, console output may have been buffered
1035  * by printk().  If this is the case, release_console_sem() emits
1036  * the output prior to releasing the semaphore.
1037  *
1038  * If there is output waiting for klogd, we wake it up.
1039  *
1040  * release_console_sem() may be called from any context.
1041  */
1042 void release_console_sem(void)
1043 {
1044         unsigned long flags;
1045         unsigned _con_start, _log_end;
1046         unsigned wake_klogd = 0;
1047
1048         if (console_suspended) {
1049                 up(&console_sem);
1050                 return;
1051         }
1052
1053         console_may_schedule = 0;
1054
1055         for ( ; ; ) {
1056                 spin_lock_irqsave(&logbuf_lock, flags);
1057                 wake_klogd |= log_start - log_end;
1058                 if (con_start == log_end)
1059                         break;                  /* Nothing to print */
1060                 _con_start = con_start;
1061                 _log_end = log_end;
1062                 con_start = log_end;            /* Flush */
1063                 spin_unlock(&logbuf_lock);
1064                 stop_critical_timings();        /* don't trace print latency */
1065                 call_console_drivers(_con_start, _log_end);
1066                 start_critical_timings();
1067                 local_irq_restore(flags);
1068         }
1069         console_locked = 0;
1070         up(&console_sem);
1071         spin_unlock_irqrestore(&logbuf_lock, flags);
1072         if (wake_klogd)
1073                 wake_up_klogd();
1074 }
1075 EXPORT_SYMBOL(release_console_sem);
1076
1077 /**
1078  * console_conditional_schedule - yield the CPU if required
1079  *
1080  * If the console code is currently allowed to sleep, and
1081  * if this CPU should yield the CPU to another task, do
1082  * so here.
1083  *
1084  * Must be called within acquire_console_sem().
1085  */
1086 void __sched console_conditional_schedule(void)
1087 {
1088         if (console_may_schedule)
1089                 cond_resched();
1090 }
1091 EXPORT_SYMBOL(console_conditional_schedule);
1092
1093 void console_unblank(void)
1094 {
1095         struct console *c;
1096
1097         /*
1098          * console_unblank can no longer be called in interrupt context unless
1099          * oops_in_progress is set to 1..
1100          */
1101         if (oops_in_progress) {
1102                 if (down_trylock(&console_sem) != 0)
1103                         return;
1104         } else
1105                 acquire_console_sem();
1106
1107         console_locked = 1;
1108         console_may_schedule = 0;
1109         for_each_console(c)
1110                 if ((c->flags & CON_ENABLED) && c->unblank)
1111                         c->unblank();
1112         release_console_sem();
1113 }
1114
1115 /*
1116  * Return the console tty driver structure and its associated index
1117  */
1118 struct tty_driver *console_device(int *index)
1119 {
1120         struct console *c;
1121         struct tty_driver *driver = NULL;
1122
1123         acquire_console_sem();
1124         for_each_console(c) {
1125                 if (!c->device)
1126                         continue;
1127                 driver = c->device(c, index);
1128                 if (driver)
1129                         break;
1130         }
1131         release_console_sem();
1132         return driver;
1133 }
1134
1135 /*
1136  * Prevent further output on the passed console device so that (for example)
1137  * serial drivers can disable console output before suspending a port, and can
1138  * re-enable output afterwards.
1139  */
1140 void console_stop(struct console *console)
1141 {
1142         acquire_console_sem();
1143         console->flags &= ~CON_ENABLED;
1144         release_console_sem();
1145 }
1146 EXPORT_SYMBOL(console_stop);
1147
1148 void console_start(struct console *console)
1149 {
1150         acquire_console_sem();
1151         console->flags |= CON_ENABLED;
1152         release_console_sem();
1153 }
1154 EXPORT_SYMBOL(console_start);
1155
1156 /*
1157  * The console driver calls this routine during kernel initialization
1158  * to register the console printing procedure with printk() and to
1159  * print any messages that were printed by the kernel before the
1160  * console driver was initialized.
1161  *
1162  * This can happen pretty early during the boot process (because of
1163  * early_printk) - sometimes before setup_arch() completes - be careful
1164  * of what kernel features are used - they may not be initialised yet.
1165  *
1166  * There are two types of consoles - bootconsoles (early_printk) and
1167  * "real" consoles (everything which is not a bootconsole) which are
1168  * handled differently.
1169  *  - Any number of bootconsoles can be registered at any time.
1170  *  - As soon as a "real" console is registered, all bootconsoles
1171  *    will be unregistered automatically.
1172  *  - Once a "real" console is registered, any attempt to register a
1173  *    bootconsoles will be rejected
1174  */
1175 void register_console(struct console *newcon)
1176 {
1177         int i;
1178         unsigned long flags;
1179         struct console *bcon = NULL;
1180
1181         /*
1182          * before we register a new CON_BOOT console, make sure we don't
1183          * already have a valid console
1184          */
1185         if (console_drivers && newcon->flags & CON_BOOT) {
1186                 /* find the last or real console */
1187                 for_each_console(bcon) {
1188                         if (!(bcon->flags & CON_BOOT)) {
1189                                 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1190                                         newcon->name, newcon->index);
1191                                 return;
1192                         }
1193                 }
1194         }
1195
1196         if (console_drivers && console_drivers->flags & CON_BOOT)
1197                 bcon = console_drivers;
1198
1199         if (preferred_console < 0 || bcon || !console_drivers)
1200                 preferred_console = selected_console;
1201
1202         if (newcon->early_setup)
1203                 newcon->early_setup();
1204
1205         /*
1206          *      See if we want to use this console driver. If we
1207          *      didn't select a console we take the first one
1208          *      that registers here.
1209          */
1210         if (preferred_console < 0) {
1211                 if (newcon->index < 0)
1212                         newcon->index = 0;
1213                 if (newcon->setup == NULL ||
1214                     newcon->setup(newcon, NULL) == 0) {
1215                         newcon->flags |= CON_ENABLED;
1216                         if (newcon->device) {
1217                                 newcon->flags |= CON_CONSDEV;
1218                                 preferred_console = 0;
1219                         }
1220                 }
1221         }
1222
1223         /*
1224          *      See if this console matches one we selected on
1225          *      the command line.
1226          */
1227         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1228                         i++) {
1229                 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1230                         continue;
1231                 if (newcon->index >= 0 &&
1232                     newcon->index != console_cmdline[i].index)
1233                         continue;
1234                 if (newcon->index < 0)
1235                         newcon->index = console_cmdline[i].index;
1236 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1237                 if (console_cmdline[i].brl_options) {
1238                         newcon->flags |= CON_BRL;
1239                         braille_register_console(newcon,
1240                                         console_cmdline[i].index,
1241                                         console_cmdline[i].options,
1242                                         console_cmdline[i].brl_options);
1243                         return;
1244                 }
1245 #endif
1246                 if (newcon->setup &&
1247                     newcon->setup(newcon, console_cmdline[i].options) != 0)
1248                         break;
1249                 newcon->flags |= CON_ENABLED;
1250                 newcon->index = console_cmdline[i].index;
1251                 if (i == selected_console) {
1252                         newcon->flags |= CON_CONSDEV;
1253                         preferred_console = selected_console;
1254                 }
1255                 break;
1256         }
1257
1258         if (!(newcon->flags & CON_ENABLED))
1259                 return;
1260
1261         /*
1262          * If we have a bootconsole, and are switching to a real console,
1263          * don't print everything out again, since when the boot console, and
1264          * the real console are the same physical device, it's annoying to
1265          * see the beginning boot messages twice
1266          */
1267         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1268                 newcon->flags &= ~CON_PRINTBUFFER;
1269
1270         /*
1271          *      Put this console in the list - keep the
1272          *      preferred driver at the head of the list.
1273          */
1274         acquire_console_sem();
1275         if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1276                 newcon->next = console_drivers;
1277                 console_drivers = newcon;
1278                 if (newcon->next)
1279                         newcon->next->flags &= ~CON_CONSDEV;
1280         } else {
1281                 newcon->next = console_drivers->next;
1282                 console_drivers->next = newcon;
1283         }
1284         if (newcon->flags & CON_PRINTBUFFER) {
1285                 /*
1286                  * release_console_sem() will print out the buffered messages
1287                  * for us.
1288                  */
1289                 spin_lock_irqsave(&logbuf_lock, flags);
1290                 con_start = log_start;
1291                 spin_unlock_irqrestore(&logbuf_lock, flags);
1292         }
1293         release_console_sem();
1294
1295         /*
1296          * By unregistering the bootconsoles after we enable the real console
1297          * we get the "console xxx enabled" message on all the consoles -
1298          * boot consoles, real consoles, etc - this is to ensure that end
1299          * users know there might be something in the kernel's log buffer that
1300          * went to the bootconsole (that they do not see on the real console)
1301          */
1302         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1303                 /* we need to iterate through twice, to make sure we print
1304                  * everything out, before we unregister the console(s)
1305                  */
1306                 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1307                         newcon->name, newcon->index);
1308                 for_each_console(bcon)
1309                         if (bcon->flags & CON_BOOT)
1310                                 unregister_console(bcon);
1311         } else {
1312                 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1313                         (newcon->flags & CON_BOOT) ? "boot" : "" ,
1314                         newcon->name, newcon->index);
1315         }
1316 }
1317 EXPORT_SYMBOL(register_console);
1318
1319 int unregister_console(struct console *console)
1320 {
1321         struct console *a, *b;
1322         int res = 1;
1323
1324 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1325         if (console->flags & CON_BRL)
1326                 return braille_unregister_console(console);
1327 #endif
1328
1329         acquire_console_sem();
1330         if (console_drivers == console) {
1331                 console_drivers=console->next;
1332                 res = 0;
1333         } else if (console_drivers) {
1334                 for (a=console_drivers->next, b=console_drivers ;
1335                      a; b=a, a=b->next) {
1336                         if (a == console) {
1337                                 b->next = a->next;
1338                                 res = 0;
1339                                 break;
1340                         }
1341                 }
1342         }
1343
1344         /*
1345          * If this isn't the last console and it has CON_CONSDEV set, we
1346          * need to set it on the next preferred console.
1347          */
1348         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1349                 console_drivers->flags |= CON_CONSDEV;
1350
1351         release_console_sem();
1352         return res;
1353 }
1354 EXPORT_SYMBOL(unregister_console);
1355
1356 static int __init disable_boot_consoles(void)
1357 {
1358         struct console *con;
1359
1360         for_each_console(con) {
1361                 if (con->flags & CON_BOOT) {
1362                         printk(KERN_INFO "turn off boot console %s%d\n",
1363                                 con->name, con->index);
1364                         unregister_console(con);
1365                 }
1366         }
1367         return 0;
1368 }
1369 late_initcall(disable_boot_consoles);
1370
1371 #if defined CONFIG_PRINTK
1372
1373 /*
1374  * printk rate limiting, lifted from the networking subsystem.
1375  *
1376  * This enforces a rate limit: not more than 10 kernel messages
1377  * every 5s to make a denial-of-service attack impossible.
1378  */
1379 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1380
1381 int printk_ratelimit(void)
1382 {
1383         return __ratelimit(&printk_ratelimit_state);
1384 }
1385 EXPORT_SYMBOL(printk_ratelimit);
1386
1387 /**
1388  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1389  * @caller_jiffies: pointer to caller's state
1390  * @interval_msecs: minimum interval between prints
1391  *
1392  * printk_timed_ratelimit() returns true if more than @interval_msecs
1393  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1394  * returned true.
1395  */
1396 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1397                         unsigned int interval_msecs)
1398 {
1399         if (*caller_jiffies == 0
1400                         || !time_in_range(jiffies, *caller_jiffies,
1401                                         *caller_jiffies
1402                                         + msecs_to_jiffies(interval_msecs))) {
1403                 *caller_jiffies = jiffies;
1404                 return true;
1405         }
1406         return false;
1407 }
1408 EXPORT_SYMBOL(printk_timed_ratelimit);
1409 #endif