init/main.c

   1 /*
   2  *  linux/init/main.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  *
   6  *  GK 2/5/95  -  Changed to support mounting root fs via NFS
   7  *  Added initrd & change_root: Werner Almesberger & Hans Lermen, Feb '96
   8  *  Moan early if gcc is old, avoiding bogus kernels - Paul Gortmaker, May '96
   9  *  Simplified starting of init:  Michael A. Griffith <grif@acm.org>
  10  */
  11
  12 #include <linux/types.h>
  13 #include <linux/module.h>
  14 #include <linux/proc_fs.h>
  15 #include <linux/kernel.h>
  16 #include <linux/syscalls.h>
  17 #include <linux/string.h>
  18 #include <linux/ctype.h>
  19 #include <linux/delay.h>
  20 #include <linux/utsname.h>
  21 #include <linux/ioport.h>
  22 #include <linux/init.h>
  23 #include <linux/smp_lock.h>
  24 #include <linux/initrd.h>
  25 #include <linux/hdreg.h>
  26 #include <linux/bootmem.h>
  27 #include <linux/tty.h>
  28 #include <linux/gfp.h>
  29 #include <linux/percpu.h>
  30 #include <linux/kmod.h>
  31 #include <linux/kernel_stat.h>
  32 #include <linux/start_kernel.h>
  33 #include <linux/security.h>
  34 #include <linux/workqueue.h>
  35 #include <linux/profile.h>
  36 #include <linux/rcupdate.h>
  37 #include <linux/moduleparam.h>
  38 #include <linux/kallsyms.h>
  39 #include <linux/writeback.h>
  40 #include <linux/cpu.h>
  41 #include <linux/cpuset.h>
  42 #include <linux/efi.h>
  43 #include <linux/taskstats_kern.h>
  44 #include <linux/delayacct.h>
  45 #include <linux/unistd.h>
  46 #include <linux/rmap.h>
  47 #include <linux/mempolicy.h>
  48 #include <linux/key.h>
  49 #include <linux/unwind.h>
  50 #include <linux/buffer_head.h>
  51 #include <linux/debug_locks.h>
  52 #include <linux/lockdep.h>
  53
  54 #include <asm/io.h>
  55 #include <asm/bugs.h>
  56 #include <asm/setup.h>
  57 #include <asm/sections.h>
  58 #include <asm/cacheflush.h>
  59
  60 #ifdef CONFIG_X86_LOCAL_APIC
  61 #include <asm/smp.h>
  62 #endif
  63
  64 /*
  65  * This is one of the first .c files built. Error out early if we have compiler
  66  * trouble.
  67  *
  68  * Versions of gcc older than that listed below may actually compile and link
  69  * okay, but the end product can have subtle run time bugs.  To avoid associated
  70  * bogus bug reports, we flatly refuse to compile with a gcc that is known to be
  71  * too old from the very beginning.
  72  */
  73 #if (__GNUC__ < 3) || (__GNUC__ == 3 && __GNUC_MINOR__ < 2)
  74 #error Sorry, your GCC is too old. It builds incorrect kernels.
  75 #endif
  76
  77 #if __GNUC__ == 4 && __GNUC_MINOR__ == 1 && __GNUC_PATCHLEVEL__ == 0
  78 #warning gcc-4.1.0 is known to miscompile the kernel.  A different compiler version is recommended.
  79 #endif
  80
  81 static int init(void *);
  82
  83 extern void init_IRQ(void);
  84 extern void fork_init(unsigned long);
  85 extern void mca_init(void);
  86 extern void sbus_init(void);
  87 extern void sysctl_init(void);
  88 extern void signals_init(void);
  89 extern void pidhash_init(void);
  90 extern void pidmap_init(void);
  91 extern void prio_tree_init(void);
  92 extern void radix_tree_init(void);
  93 extern void free_initmem(void);
  94 extern void populate_rootfs(void);
  95 extern void driver_init(void);
  96 extern void prepare_namespace(void);
  97 #ifdef  CONFIG_ACPI
  98 extern void acpi_early_init(void);
  99 #else
 100 static inline void acpi_early_init(void) { }
 101 #endif
 102 #ifndef CONFIG_DEBUG_RODATA
 103 static inline void mark_rodata_ro(void) { }
 104 #endif
 105
 106 #ifdef CONFIG_TC
 107 extern void tc_init(void);
 108 #endif
 109
 110 enum system_states system_state;
 111 EXPORT_SYMBOL(system_state);
 112
 113 /*
 114  * Boot command-line arguments
 115  */
 116 #define MAX_INIT_ARGS CONFIG_INIT_ENV_ARG_LIMIT
 117 #define MAX_INIT_ENVS CONFIG_INIT_ENV_ARG_LIMIT
 118
 119 extern void time_init(void);
 120 /* Default late time init is NULL. archs can override this later. */
 121 void (*late_time_init)(void);
 122 extern void softirq_init(void);
 123
 124 /* Untouched command line (eg. for /proc) saved by arch-specific code. */
 125 char saved_command_line[COMMAND_LINE_SIZE];
 126
 127 static char *execute_command;
 128 static char *ramdisk_execute_command;
 129
 130 /* Setup configured maximum number of CPUs to activate */
 131 static unsigned int max_cpus = NR_CPUS;
 132
 133 /*
 134  * If set, this is an indication to the drivers that reset the underlying
 135  * device before going ahead with the initialization otherwise driver might
 136  * rely on the BIOS and skip the reset operation.
 137  *
 138  * This is useful if kernel is booting in an unreliable environment.
 139  * For ex. kdump situaiton where previous kernel has crashed, BIOS has been
 140  * skipped and devices will be in unknown state.
 141  */
 142 unsigned int reset_devices;
 143 EXPORT_SYMBOL(reset_devices);
 144
 145 /*
 146  * Setup routine for controlling SMP activation
 147  *
 148  * Command-line option of "nosmp" or "maxcpus=0" will disable SMP
 149  * activation entirely (the MPS table probe still happens, though).
 150  *
 151  * Command-line option of "maxcpus=<NUM>", where <NUM> is an integer
 152  * greater than 0, limits the maximum number of CPUs activated in
 153  * SMP mode to <NUM>.
 154  */
 155 static int __init nosmp(char *str)
 156 {
 157         max_cpus = 0;
 158         return 1;
 159 }
 160
 161 __setup("nosmp", nosmp);
 162
 163 static int __init maxcpus(char *str)
 164 {
 165         get_option(&str, &max_cpus);
 166         return 1;
 167 }
 168
 169 __setup("maxcpus=", maxcpus);
 170
 171 static int __init set_reset_devices(char *str)
 172 {
 173         reset_devices = 1;
 174         return 1;
 175 }
 176
 177 __setup("reset_devices", set_reset_devices);
 178
 179 static char * argv_init[MAX_INIT_ARGS+2] = { "init", NULL, };
 180 char * envp_init[MAX_INIT_ENVS+2] = { "HOME=/", "TERM=linux", NULL, };
 181 static const char *panic_later, *panic_param;
 182
 183 extern struct obs_kernel_param __setup_start[], __setup_end[];
 184
 185 static int __init obsolete_checksetup(char *line)
 186 {
 187         struct obs_kernel_param *p;
 188         int had_early_param = 0;
 189
 190         p = __setup_start;
 191         do {
 192                 int n = strlen(p->str);
 193                 if (!strncmp(line, p->str, n)) {
 194                         if (p->early) {
 195                                 /* Already done in parse_early_param?
 196                                  * (Needs exact match on param part).
 197                                  * Keep iterating, as we can have early
 198                                  * params and __setups of same names 8( */
 199                                 if (line[n] == '\0' || line[n] == '=')
 200                                         had_early_param = 1;
 201                         } else if (!p->setup_func) {
 202                                 printk(KERN_WARNING "Parameter %s is obsolete,"
 203                                        " ignored\n", p->str);
 204                                 return 1;
 205                         } else if (p->setup_func(line + n))
 206                                 return 1;
 207                 }
 208                 p++;
 209         } while (p < __setup_end);
 210
 211         return had_early_param;
 212 }
 213
 214 /*
 215  * This should be approx 2 Bo*oMips to start (note initial shift), and will
 216  * still work even if initially too large, it will just take slightly longer
 217  */
 218 unsigned long loops_per_jiffy = (1<<12);
 219
 220 EXPORT_SYMBOL(loops_per_jiffy);
 221
 222 static int __init debug_kernel(char *str)
 223 {
 224         if (*str)
 225                 return 0;
 226         console_loglevel = 10;
 227         return 1;
 228 }
 229
 230 static int __init quiet_kernel(char *str)
 231 {
 232         if (*str)
 233                 return 0;
 234         console_loglevel = 4;
 235         return 1;
 236 }
 237
 238 __setup("debug", debug_kernel);
 239 __setup("quiet", quiet_kernel);
 240
 241 static int __init loglevel(char *str)
 242 {
 243         get_option(&str, &console_loglevel);
 244         return 1;
 245 }
 246
 247 __setup("loglevel=", loglevel);
 248
 249 /*
 250  * Unknown boot options get handed to init, unless they look like
 251  * failed parameters
 252  */
 253 static int __init unknown_bootoption(char *param, char *val)
 254 {
 255         /* Change NUL term back to "=", to make "param" the whole string. */
 256         if (val) {
 257                 /* param=val or param="val"? */
 258                 if (val == param+strlen(param)+1)
 259                         val[-1] = '=';
 260                 else if (val == param+strlen(param)+2) {
 261                         val[-2] = '=';
 262                         memmove(val-1, val, strlen(val)+1);
 263                         val--;
 264                 } else
 265                         BUG();
 266         }
 267
 268         /* Handle obsolete-style parameters */
 269         if (obsolete_checksetup(param))
 270                 return 0;
 271
 272         /*
 273          * Preemptive maintenance for "why didn't my mispelled command
 274          * line work?"
 275          */
 276         if (strchr(param, '.') && (!val || strchr(param, '.') < val)) {
 277                 printk(KERN_ERR "Unknown boot option `%s': ignoring\n", param);
 278                 return 0;
 279         }
 280
 281         if (panic_later)
 282                 return 0;
 283
 284         if (val) {
 285                 /* Environment option */
 286                 unsigned int i;
 287                 for (i = 0; envp_init[i]; i++) {
 288                         if (i == MAX_INIT_ENVS) {
 289                                 panic_later = "Too many boot env vars at `%s'";
 290                                 panic_param = param;
 291                         }
 292                         if (!strncmp(param, envp_init[i], val - param))
 293                                 break;
 294                 }
 295                 envp_init[i] = param;
 296         } else {
 297                 /* Command line option */
 298                 unsigned int i;
 299                 for (i = 0; argv_init[i]; i++) {
 300                         if (i == MAX_INIT_ARGS) {
 301                                 panic_later = "Too many boot init vars at `%s'";
 302                                 panic_param = param;
 303                         }
 304                 }
 305                 argv_init[i] = param;
 306         }
 307         return 0;
 308 }
 309
 310 static int __init init_setup(char *str)
 311 {
 312         unsigned int i;
 313
 314         execute_command = str;
 315         /*
 316          * In case LILO is going to boot us with default command line,
 317          * it prepends "auto" before the whole cmdline which makes
 318          * the shell think it should execute a script with such name.
 319          * So we ignore all arguments entered _before_ init=... [MJ]
 320          */
 321         for (i = 1; i < MAX_INIT_ARGS; i++)
 322                 argv_init[i] = NULL;
 323         return 1;
 324 }
 325 __setup("init=", init_setup);
 326
 327 static int __init rdinit_setup(char *str)
 328 {
 329         unsigned int i;
 330
 331         ramdisk_execute_command = str;
 332         /* See "auto" comment in init_setup */
 333         for (i = 1; i < MAX_INIT_ARGS; i++)
 334                 argv_init[i] = NULL;
 335         return 1;
 336 }
 337 __setup("rdinit=", rdinit_setup);
 338
 339 #ifndef CONFIG_SMP
 340
 341 #ifdef CONFIG_X86_LOCAL_APIC
 342 static void __init smp_init(void)
 343 {
 344         APIC_init_uniprocessor();
 345 }
 346 #else
 347 #define smp_init()      do { } while (0)
 348 #endif
 349
 350 static inline void setup_per_cpu_areas(void) { }
 351 static inline void smp_prepare_cpus(unsigned int maxcpus) { }
 352
 353 #else
 354
 355 #ifdef __GENERIC_PER_CPU
 356 unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
 357
 358 EXPORT_SYMBOL(__per_cpu_offset);
 359
 360 static void __init setup_per_cpu_areas(void)
 361 {
 362         unsigned long size, i;
 363         char *ptr;
 364         unsigned long nr_possible_cpus = num_possible_cpus();
 365
 366         /* Copy section for each CPU (we discard the original) */
 367         size = ALIGN(__per_cpu_end - __per_cpu_start, SMP_CACHE_BYTES);
 368 #ifdef CONFIG_MODULES
 369         if (size < PERCPU_ENOUGH_ROOM)
 370                 size = PERCPU_ENOUGH_ROOM;
 371 #endif
 372         ptr = alloc_bootmem(size * nr_possible_cpus);
 373
 374         for_each_possible_cpu(i) {
 375                 __per_cpu_offset[i] = ptr - __per_cpu_start;
 376                 memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start);
 377                 ptr += size;
 378         }
 379 }
 380 #endif /* !__GENERIC_PER_CPU */
 381
 382 /* Called by boot processor to activate the rest. */
 383 static void __init smp_init(void)
 384 {
 385         unsigned int i;
 386
 387         /* FIXME: This should be done in userspace --RR */
 388         for_each_present_cpu(i) {
 389                 if (num_online_cpus() >= max_cpus)
 390                         break;
 391                 if (!cpu_online(i))
 392                         cpu_up(i);
 393         }
 394
 395         /* Any cleanup work */
 396         printk(KERN_INFO "Brought up %ld CPUs\n", (long)num_online_cpus());
 397         smp_cpus_done(max_cpus);
 398 #if 0
 399         /* Get other processors into their bootup holding patterns. */
 400
 401         smp_commence();
 402 #endif
 403 }
 404
 405 #endif
 406
 407 /*
 408  * We need to finalize in a non-__init function or else race conditions
 409  * between the root thread and the init thread may cause start_kernel to
 410  * be reaped by free_initmem before the root thread has proceeded to
 411  * cpu_idle.
 412  *
 413  * gcc-3.4 accidentally inlines this function, so use noinline.
 414  */
 415
 416 static void noinline rest_init(void)
 417         __releases(kernel_lock)
 418 {
 419         kernel_thread(init, NULL, CLONE_FS | CLONE_SIGHAND);
 420         numa_default_policy();
 421         unlock_kernel();
 422
 423         /*
 424          * The boot idle thread must execute schedule()
 425          * at least one to get things moving:
 426          */
 427         preempt_enable_no_resched();
 428         schedule();
 429         preempt_disable();
 430
 431         /* Call into cpu_idle with preempt disabled */
 432         cpu_idle();
 433 }
 434
 435 /* Check for early params. */
 436 static int __init do_early_param(char *param, char *val)
 437 {
 438         struct obs_kernel_param *p;
 439
 440         for (p = __setup_start; p < __setup_end; p++) {
 441                 if (p->early && strcmp(param, p->str) == 0) {
 442                         if (p->setup_func(val) != 0)
 443                                 printk(KERN_WARNING
 444                                        "Malformed early option '%s'\n", param);
 445                 }
 446         }
 447         /* We accept everything at this stage. */
 448         return 0;
 449 }
 450
 451 /* Arch code calls this early on, or if not, just before other parsing. */
 452 void __init parse_early_param(void)
 453 {
 454         static __initdata int done = 0;
 455         static __initdata char tmp_cmdline[COMMAND_LINE_SIZE];
 456
 457         if (done)
 458                 return;
 459
 460         /* All fall through to do_early_param. */
 461         strlcpy(tmp_cmdline, saved_command_line, COMMAND_LINE_SIZE);
 462         parse_args("early options", tmp_cmdline, NULL, 0, do_early_param);
 463         done = 1;
 464 }
 465
 466 /*
 467  *      Activate the first processor.
 468  */
 469
 470 static void __init boot_cpu_init(void)
 471 {
 472         int cpu = smp_processor_id();
 473         /* Mark the boot cpu "present", "online" etc for SMP and UP case */
 474         cpu_set(cpu, cpu_online_map);
 475         cpu_set(cpu, cpu_present_map);
 476         cpu_set(cpu, cpu_possible_map);
 477 }
 478
 479 void __init __attribute__((weak)) smp_setup_processor_id(void)
 480 {
 481 }
 482
 483 asmlinkage void __init start_kernel(void)
 484 {
 485         char * command_line;
 486         extern struct kernel_param __start___param[], __stop___param[];
 487
 488         smp_setup_processor_id();
 489
 490         /*
 491          * Need to run as early as possible, to initialize the
 492          * lockdep hash:
 493          */
 494         unwind_init();
 495         lockdep_init();
 496
 497         local_irq_disable();
 498         early_boot_irqs_off();
 499         early_init_irq_lock_class();
 500
 501 /*
 502  * Interrupts are still disabled. Do necessary setups, then
 503  * enable them
 504  */
 505         lock_kernel();
 506         boot_cpu_init();
 507         page_address_init();
 508         printk(KERN_NOTICE);
 509         printk(linux_banner);
 510         setup_arch(&command_line);
 511         unwind_setup();
 512         setup_per_cpu_areas();
 513         smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */
 514
 515         /*
 516          * Set up the scheduler prior starting any interrupts (such as the
 517          * timer interrupt). Full topology setup happens at smp_init()
 518          * time - but meanwhile we still have a functioning scheduler.
 519          */
 520         sched_init();
 521         /*
 522          * Disable preemption - early bootup scheduling is extremely
 523          * fragile until we cpu_idle() for the first time.
 524          */
 525         preempt_disable();
 526         build_all_zonelists();
 527         page_alloc_init();
 528         printk(KERN_NOTICE "Kernel command line: %s\n", saved_command_line);
 529         parse_early_param();
 530         parse_args("Booting kernel", command_line, __start___param,
 531                    __stop___param - __start___param,
 532                    &unknown_bootoption);
 533         sort_main_extable();
 534         trap_init();
 535         rcu_init();
 536         init_IRQ();
 537         pidhash_init();
 538         init_timers();
 539         hrtimers_init();
 540         softirq_init();
 541         timekeeping_init();
 542         time_init();
 543         profile_init();
 544         if (!irqs_disabled())
 545                 printk("start_kernel(): bug: interrupts were enabled early\n");
 546         early_boot_irqs_on();
 547         local_irq_enable();
 548
 549         /*
 550          * HACK ALERT! This is early. We're enabling the console before
 551          * we've done PCI setups etc, and console_init() must be aware of
 552          * this. But we do want output early, in case something goes wrong.
 553          */
 554         console_init();
 555         if (panic_later)
 556                 panic(panic_later, panic_param);
 557
 558         lockdep_info();
 559
 560         /*
 561          * Need to run this when irqs are enabled, because it wants
 562          * to self-test [hard/soft]-irqs on/off lock inversion bugs
 563          * too:
 564          */
 565         locking_selftest();
 566
 567 #ifdef CONFIG_BLK_DEV_INITRD
 568         if (initrd_start && !initrd_below_start_ok &&
 569                         initrd_start < min_low_pfn << PAGE_SHIFT) {
 570                 printk(KERN_CRIT "initrd overwritten (0x%08lx < 0x%08lx) - "
 571                     "disabling it.\n",initrd_start,min_low_pfn << PAGE_SHIFT);
 572                 initrd_start = 0;
 573         }
 574 #endif
 575         vfs_caches_init_early();
 576         cpuset_init_early();
 577         mem_init();
 578         kmem_cache_init();
 579         setup_per_cpu_pageset();
 580         numa_policy_init();
 581         if (late_time_init)
 582                 late_time_init();
 583         calibrate_delay();
 584         pidmap_init();
 585         pgtable_cache_init();
 586         prio_tree_init();
 587         anon_vma_init();
 588 #ifdef CONFIG_X86
 589         if (efi_enabled)
 590                 efi_enter_virtual_mode();
 591 #endif
 592         fork_init(num_physpages);
 593         proc_caches_init();
 594         buffer_init();
 595         unnamed_dev_init();
 596         key_init();
 597         security_init();
 598         vfs_caches_init(num_physpages);
 599         radix_tree_init();
 600         signals_init();
 601         /* rootfs populating might need page-writeback */
 602         page_writeback_init();
 603 #ifdef CONFIG_PROC_FS
 604         proc_root_init();
 605 #endif
 606         cpuset_init();
 607         taskstats_init_early();
 608         delayacct_init();
 609
 610         check_bugs();
 611
 612         acpi_early_init(); /* before LAPIC and SMP init */
 613
 614         /* Do the rest non-__init'ed, we're now alive */
 615         rest_init();
 616 }
 617
 618 static int __initdata initcall_debug;
 619
 620 static int __init initcall_debug_setup(char *str)
 621 {
 622         initcall_debug = 1;
 623         return 1;
 624 }
 625 __setup("initcall_debug", initcall_debug_setup);
 626
 627 struct task_struct *child_reaper = &init_task;
 628
 629 extern initcall_t __initcall_start[], __initcall_end[];
 630
 631 static void __init do_initcalls(void)
 632 {
 633         initcall_t *call;
 634         int count = preempt_count();
 635
 636         for (call = __initcall_start; call < __initcall_end; call++) {
 637                 char *msg = NULL;
 638                 char msgbuf[40];
 639                 int result;
 640
 641                 if (initcall_debug) {
 642                         printk("Calling initcall 0x%p", *call);
 643                         print_fn_descriptor_symbol(": %s()",
 644                                         (unsigned long) *call);
 645                         printk("\n");
 646                 }
 647
 648                 result = (*call)();
 649
 650                 if (result && result != -ENODEV && initcall_debug) {
 651                         sprintf(msgbuf, "error code %d", result);
 652                         msg = msgbuf;
 653                 }
 654                 if (preempt_count() != count) {
 655                         msg = "preemption imbalance";
 656                         preempt_count() = count;
 657                 }
 658                 if (irqs_disabled()) {
 659                         msg = "disabled interrupts";
 660                         local_irq_enable();
 661                 }
 662                 if (msg) {
 663                         printk(KERN_WARNING "initcall at 0x%p", *call);
 664                         print_fn_descriptor_symbol(": %s()",
 665                                         (unsigned long) *call);
 666                         printk(": returned with %s\n", msg);
 667                 }
 668         }
 669
 670         /* Make sure there is no pending stuff from the initcall sequence */
 671         flush_scheduled_work();
 672 }
 673
 674 /*
 675  * Ok, the machine is now initialized. None of the devices
 676  * have been touched yet, but the CPU subsystem is up and
 677  * running, and memory and process management works.
 678  *
 679  * Now we can finally start doing some real work..
 680  */
 681 static void __init do_basic_setup(void)
 682 {
 683         /* drivers will send hotplug events */
 684         init_workqueues();
 685         usermodehelper_init();
 686         driver_init();
 687
 688 #ifdef CONFIG_SYSCTL
 689         sysctl_init();
 690 #endif
 691
 692         do_initcalls();
 693 }
 694
 695 static void do_pre_smp_initcalls(void)
 696 {
 697         extern int spawn_ksoftirqd(void);
 698 #ifdef CONFIG_SMP
 699         extern int migration_init(void);
 700
 701         migration_init();
 702 #endif
 703         spawn_ksoftirqd();
 704         spawn_softlockup_task();
 705 }
 706
 707 static void run_init_process(char *init_filename)
 708 {
 709         argv_init[0] = init_filename;
 710         kernel_execve(init_filename, argv_init, envp_init);
 711 }
 712
 713 static int init(void * unused)
 714 {
 715         lock_kernel();
 716         /*
 717          * init can run on any cpu.
 718          */
 719         set_cpus_allowed(current, CPU_MASK_ALL);
 720         /*
 721          * Tell the world that we're going to be the grim
 722          * reaper of innocent orphaned children.
 723          *
 724          * We don't want people to have to make incorrect
 725          * assumptions about where in the task array this
 726          * can be found.
 727          */
 728         child_reaper = current;
 729
 730         cad_pid = task_pid(current);
 731
 732         smp_prepare_cpus(max_cpus);
 733
 734         do_pre_smp_initcalls();
 735
 736         smp_init();
 737         sched_init_smp();
 738
 739         cpuset_init_smp();
 740
 741         /*
 742          * Do this before initcalls, because some drivers want to access
 743          * firmware files.
 744          */
 745         populate_rootfs();
 746
 747         do_basic_setup();
 748
 749         /*
 750          * check if there is an early userspace init.  If yes, let it do all
 751          * the work
 752          */
 753
 754         if (!ramdisk_execute_command)
 755                 ramdisk_execute_command = "/init";
 756
 757         if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
 758                 ramdisk_execute_command = NULL;
 759                 prepare_namespace();
 760         }
 761
 762         /*
 763          * Ok, we have completed the initial bootup, and
 764          * we're essentially up and running. Get rid of the
 765          * initmem segments and start the user-mode stuff..
 766          */
 767         free_initmem();
 768         unlock_kernel();
 769         mark_rodata_ro();
 770         system_state = SYSTEM_RUNNING;
 771         numa_default_policy();
 772
 773         if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
 774                 printk(KERN_WARNING "Warning: unable to open an initial console.\n");
 775
 776         (void) sys_dup(0);
 777         (void) sys_dup(0);
 778
 779         if (ramdisk_execute_command) {
 780                 run_init_process(ramdisk_execute_command);
 781                 printk(KERN_WARNING "Failed to execute %s\n",
 782                                 ramdisk_execute_command);
 783         }
 784
 785         /*
 786          * We try each of these until one succeeds.
 787          *
 788          * The Bourne shell can be used instead of init if we are
 789          * trying to recover a really broken machine.
 790          */
 791         if (execute_command) {
 792                 run_init_process(execute_command);
 793                 printk(KERN_WARNING "Failed to execute %s.  Attempting "
 794                                         "defaults...\n", execute_command);
 795         }
 796         run_init_process("/sbin/init");
 797         run_init_process("/etc/init");
 798         run_init_process("/bin/init");
 799         run_init_process("/bin/sh");
 800
 801         panic("No init found.  Try passing init= option to kernel.");
 802 }