arch/um/os-Linux/skas/process.c

   1 /*
   2  * Copyright (C) 2002- 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   3  * Licensed under the GPL
   4  */
   5
   6 #include <stdlib.h>
   7 #include <unistd.h>
   8 #include <sched.h>
   9 #include <errno.h>
  10 #include <string.h>
  11 #include <sys/mman.h>
  12 #include <sys/ptrace.h>
  13 #include <sys/wait.h>
  14 #include <asm/unistd.h>
  15 #include "as-layout.h"
  16 #include "chan_user.h"
  17 #include "kern_constants.h"
  18 #include "mem.h"
  19 #include "os.h"
  20 #include "process.h"
  21 #include "proc_mm.h"
  22 #include "ptrace_user.h"
  23 #include "registers.h"
  24 #include "skas.h"
  25 #include "skas_ptrace.h"
  26 #include "user.h"
  27 #include "sysdep/stub.h"
  28
  29 int is_skas_winch(int pid, int fd, void *data)
  30 {
  31         if (pid != getpgrp())
  32                 return 0;
  33
  34         register_winch_irq(-1, fd, -1, data, 0);
  35         return 1;
  36 }
  37
  38 static int ptrace_dump_regs(int pid)
  39 {
  40         unsigned long regs[MAX_REG_NR];
  41         int i;
  42
  43         if (ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
  44                 return -errno;
  45
  46         printk(UM_KERN_ERR "Stub registers -\n");
  47         for (i = 0; i < ARRAY_SIZE(regs); i++)
  48                 printk(UM_KERN_ERR "\t%d - %lx\n", i, regs[i]);
  49
  50         return 0;
  51 }
  52
  53 /*
  54  * Signals that are OK to receive in the stub - we'll just continue it.
  55  * SIGWINCH will happen when UML is inside a detached screen.
  56  */
  57 #define STUB_SIG_MASK ((1 << SIGVTALRM) | (1 << SIGWINCH))
  58
  59 /* Signals that the stub will finish with - anything else is an error */
  60 #define STUB_DONE_MASK ((1 << SIGUSR1) | (1 << SIGTRAP))
  61
  62 void wait_stub_done(int pid)
  63 {
  64         int n, status, err;
  65
  66         while (1) {
  67                 CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
  68                 if ((n < 0) || !WIFSTOPPED(status))
  69                         goto bad_wait;
  70
  71                 if (((1 << WSTOPSIG(status)) & STUB_SIG_MASK) == 0)
  72                         break;
  73
  74                 err = ptrace(PTRACE_CONT, pid, 0, 0);
  75                 if (err)
  76                         panic("wait_stub_done : continue failed, errno = %d\n",
  77                               errno);
  78         }
  79
  80         if (((1 << WSTOPSIG(status)) & STUB_DONE_MASK) != 0)
  81                 return;
  82
  83 bad_wait:
  84         err = ptrace_dump_regs(pid);
  85         if (err)
  86                 printk(UM_KERN_ERR "Failed to get registers from stub, "
  87                        "errno = %d\n", -err);
  88         panic("wait_stub_done : failed to wait for SIGUSR1/SIGTRAP, pid = %d, "
  89               "n = %d, errno = %d, status = 0x%x\n", pid, n, errno, status);
  90 }
  91
  92 extern unsigned long current_stub_stack(void);
  93
  94 void get_skas_faultinfo(int pid, struct faultinfo * fi)
  95 {
  96         int err;
  97
  98         if (ptrace_faultinfo) {
  99                 err = ptrace(PTRACE_FAULTINFO, pid, 0, fi);
 100                 if (err)
 101                         panic("get_skas_faultinfo - PTRACE_FAULTINFO failed, "
 102                               "errno = %d\n", errno);
 103
 104                 /* Special handling for i386, which has different structs */
 105                 if (sizeof(struct ptrace_faultinfo) < sizeof(struct faultinfo))
 106                         memset((char *)fi + sizeof(struct ptrace_faultinfo), 0,
 107                                sizeof(struct faultinfo) -
 108                                sizeof(struct ptrace_faultinfo));
 109         }
 110         else {
 111                 err = ptrace(PTRACE_CONT, pid, 0, SIGSEGV);
 112                 if (err)
 113                         panic("Failed to continue stub, pid = %d, errno = %d\n",
 114                               pid, errno);
 115                 wait_stub_done(pid);
 116
 117                 /*
 118                  * faultinfo is prepared by the stub-segv-handler at start of
 119                  * the stub stack page. We just have to copy it.
 120                  */
 121                 memcpy(fi, (void *)current_stub_stack(), sizeof(*fi));
 122         }
 123 }
 124
 125 static void handle_segv(int pid, struct uml_pt_regs * regs)
 126 {
 127         get_skas_faultinfo(pid, &regs->faultinfo);
 128         segv(regs->faultinfo, 0, 1, NULL);
 129 }
 130
 131 /*
 132  * To use the same value of using_sysemu as the caller, ask it that value
 133  * (in local_using_sysemu
 134  */
 135 static void handle_trap(int pid, struct uml_pt_regs *regs,
 136                         int local_using_sysemu)
 137 {
 138         int err, status;
 139
 140         /* Mark this as a syscall */
 141         UPT_SYSCALL_NR(regs) = PT_SYSCALL_NR(regs->gp);
 142
 143         if (!local_using_sysemu)
 144         {
 145                 err = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_NR_OFFSET,
 146                              __NR_getpid);
 147                 if (err < 0)
 148                         panic("handle_trap - nullifying syscall failed, "
 149                               "errno = %d\n", errno);
 150
 151                 err = ptrace(PTRACE_SYSCALL, pid, 0, 0);
 152                 if (err < 0)
 153                         panic("handle_trap - continuing to end of syscall "
 154                               "failed, errno = %d\n", errno);
 155
 156                 CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED));
 157                 if ((err < 0) || !WIFSTOPPED(status) ||
 158                    (WSTOPSIG(status) != SIGTRAP + 0x80)) {
 159                         err = ptrace_dump_regs(pid);
 160                         if (err)
 161                                 printk(UM_KERN_ERR "Failed to get registers "
 162                                        "from process, errno = %d\n", -err);
 163                         panic("handle_trap - failed to wait at end of syscall, "
 164                               "errno = %d, status = %d\n", errno, status);
 165                 }
 166         }
 167
 168         handle_syscall(regs);
 169 }
 170
 171 extern int __syscall_stub_start;
 172
 173 static int userspace_tramp(void *stack)
 174 {
 175         void *addr;
 176         int err;
 177
 178         ptrace(PTRACE_TRACEME, 0, 0, 0);
 179
 180         signal(SIGTERM, SIG_DFL);
 181         err = set_interval();
 182         if (err)
 183                 panic("userspace_tramp - setting timer failed, errno = %d\n",
 184                       err);
 185
 186         if (!proc_mm) {
 187                 /*
 188                  * This has a pte, but it can't be mapped in with the usual
 189                  * tlb_flush mechanism because this is part of that mechanism
 190                  */
 191                 int fd;
 192                 unsigned long long offset;
 193                 fd = phys_mapping(to_phys(&__syscall_stub_start), &offset);
 194                 addr = mmap64((void *) STUB_CODE, UM_KERN_PAGE_SIZE,
 195                               PROT_EXEC, MAP_FIXED | MAP_PRIVATE, fd, offset);
 196                 if (addr == MAP_FAILED) {
 197                         printk(UM_KERN_ERR "mapping mmap stub at 0x%lx failed, "
 198                                "errno = %d\n", STUB_CODE, errno);
 199                         exit(1);
 200                 }
 201
 202                 if (stack != NULL) {
 203                         fd = phys_mapping(to_phys(stack), &offset);
 204                         addr = mmap((void *) STUB_DATA,
 205                                     UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE,
 206                                     MAP_FIXED | MAP_SHARED, fd, offset);
 207                         if (addr == MAP_FAILED) {
 208                                 printk(UM_KERN_ERR "mapping segfault stack "
 209                                        "at 0x%lx failed, errno = %d\n",
 210                                        STUB_DATA, errno);
 211                                 exit(1);
 212                         }
 213                 }
 214         }
 215         if (!ptrace_faultinfo && (stack != NULL)) {
 216                 struct sigaction sa;
 217
 218                 unsigned long v = STUB_CODE +
 219                                   (unsigned long) stub_segv_handler -
 220                                   (unsigned long) &__syscall_stub_start;
 221
 222                 set_sigstack((void *) STUB_DATA, UM_KERN_PAGE_SIZE);
 223                 sigemptyset(&sa.sa_mask);
 224                 sigaddset(&sa.sa_mask, SIGIO);
 225                 sigaddset(&sa.sa_mask, SIGWINCH);
 226                 sigaddset(&sa.sa_mask, SIGVTALRM);
 227                 sigaddset(&sa.sa_mask, SIGUSR1);
 228                 sa.sa_flags = SA_ONSTACK;
 229                 sa.sa_handler = (void *) v;
 230                 sa.sa_restorer = NULL;
 231                 if (sigaction(SIGSEGV, &sa, NULL) < 0)
 232                         panic("userspace_tramp - setting SIGSEGV handler "
 233                               "failed - errno = %d\n", errno);
 234         }
 235
 236         kill(os_getpid(), SIGSTOP);
 237         return 0;
 238 }
 239
 240 /* Each element set once, and only accessed by a single processor anyway */
 241 #undef NR_CPUS
 242 #define NR_CPUS 1
 243 int userspace_pid[NR_CPUS];
 244
 245 int start_userspace(unsigned long stub_stack)
 246 {
 247         void *stack;
 248         unsigned long sp;
 249         int pid, status, n, flags;
 250
 251         stack = mmap(NULL, UM_KERN_PAGE_SIZE,
 252                      PROT_READ | PROT_WRITE | PROT_EXEC,
 253                      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 254         if (stack == MAP_FAILED)
 255                 panic("start_userspace : mmap failed, errno = %d", errno);
 256         sp = (unsigned long) stack + UM_KERN_PAGE_SIZE - sizeof(void *);
 257
 258         flags = CLONE_FILES | SIGCHLD;
 259         if (proc_mm)
 260                 flags |= CLONE_VM;
 261
 262         pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack);
 263         if (pid < 0)
 264                 panic("start_userspace : clone failed, errno = %d", errno);
 265
 266         do {
 267                 CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
 268                 if (n < 0)
 269                         panic("start_userspace : wait failed, errno = %d",
 270                               errno);
 271         } while (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGVTALRM));
 272
 273         if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP))
 274                 panic("start_userspace : expected SIGSTOP, got status = %d",
 275                       status);
 276
 277         if (ptrace(PTRACE_OLDSETOPTIONS, pid, NULL,
 278                    (void *) PTRACE_O_TRACESYSGOOD) < 0)
 279                 panic("start_userspace : PTRACE_OLDSETOPTIONS failed, "
 280                       "errno = %d\n", errno);
 281
 282         if (munmap(stack, UM_KERN_PAGE_SIZE) < 0)
 283                 panic("start_userspace : munmap failed, errno = %d\n", errno);
 284
 285         return pid;
 286 }
 287
 288 void userspace(struct uml_pt_regs *regs)
 289 {
 290         struct itimerval timer;
 291         unsigned long long nsecs, now;
 292         int err, status, op, pid = userspace_pid[0];
 293         /* To prevent races if using_sysemu changes under us.*/
 294         int local_using_sysemu;
 295
 296         if (getitimer(ITIMER_VIRTUAL, &timer))
 297                 printk("Failed to get itimer, errno = %d\n", errno);
 298         nsecs = timer.it_value.tv_sec * UM_NSEC_PER_SEC +
 299                 timer.it_value.tv_usec * UM_NSEC_PER_USEC;
 300         nsecs += os_nsecs();
 301
 302         while (1) {
 303                 restore_registers(pid, regs);
 304
 305                 /* Now we set local_using_sysemu to be used for one loop */
 306                 local_using_sysemu = get_using_sysemu();
 307
 308                 op = SELECT_PTRACE_OPERATION(local_using_sysemu,
 309                                              singlestepping(NULL));
 310
 311                 err = ptrace(op, pid, 0, 0);
 312                 if (err)
 313                         panic("userspace - could not resume userspace process, "
 314                               "pid=%d, ptrace operation = %d, errno = %d\n",
 315                               pid, op, errno);
 316
 317                 CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED));
 318                 if (err < 0)
 319                         panic("userspace - waitpid failed, errno = %d\n",
 320                               errno);
 321
 322                 regs->is_user = 1;
 323                 save_registers(pid, regs);
 324                 UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */
 325
 326                 if (WIFSTOPPED(status)) {
 327                         int sig = WSTOPSIG(status);
 328                         switch(sig) {
 329                         case SIGSEGV:
 330                                 if (PTRACE_FULL_FAULTINFO ||
 331                                     !ptrace_faultinfo) {
 332                                         get_skas_faultinfo(pid,
 333                                                            &regs->faultinfo);
 334                                         (*sig_info[SIGSEGV])(SIGSEGV, regs);
 335                                 }
 336                                 else handle_segv(pid, regs);
 337                                 break;
 338                         case SIGTRAP + 0x80:
 339                                 handle_trap(pid, regs, local_using_sysemu);
 340                                 break;
 341                         case SIGTRAP:
 342                                 relay_signal(SIGTRAP, regs);
 343                                 break;
 344                         case SIGVTALRM:
 345                                 now = os_nsecs();
 346                                 if(now < nsecs)
 347                                         break;
 348                                 block_signals();
 349                                 (*sig_info[sig])(sig, regs);
 350                                 unblock_signals();
 351                                 nsecs = timer.it_value.tv_sec *
 352                                         UM_NSEC_PER_SEC +
 353                                         timer.it_value.tv_usec *
 354                                         UM_NSEC_PER_USEC;
 355                                 nsecs += os_nsecs();
 356                                 break;
 357                         case SIGIO:
 358                         case SIGILL:
 359                         case SIGBUS:
 360                         case SIGFPE:
 361                         case SIGWINCH:
 362                                 block_signals();
 363                                 (*sig_info[sig])(sig, regs);
 364                                 unblock_signals();
 365                                 break;
 366                         default:
 367                                 printk(UM_KERN_ERR "userspace - child stopped "
 368                                        "with signal %d\n", sig);
 369                         }
 370                         pid = userspace_pid[0];
 371                         interrupt_end();
 372
 373                         /* Avoid -ERESTARTSYS handling in host */
 374                         if (PT_SYSCALL_NR_OFFSET != PT_SYSCALL_RET_OFFSET)
 375                                 PT_SYSCALL_NR(regs->gp) = -1;
 376                 }
 377         }
 378 }
 379
 380 static unsigned long thread_regs[MAX_REG_NR];
 381
 382 static int __init init_thread_regs(void)
 383 {
 384         get_safe_registers(thread_regs);
 385         /* Set parent's instruction pointer to start of clone-stub */
 386         thread_regs[REGS_IP_INDEX] = STUB_CODE +
 387                                 (unsigned long) stub_clone_handler -
 388                                 (unsigned long) &__syscall_stub_start;
 389         thread_regs[REGS_SP_INDEX] = STUB_DATA + UM_KERN_PAGE_SIZE -
 390                 sizeof(void *);
 391 #ifdef __SIGNAL_FRAMESIZE
 392         thread_regs[REGS_SP_INDEX] -= __SIGNAL_FRAMESIZE;
 393 #endif
 394         return 0;
 395 }
 396
 397 __initcall(init_thread_regs);
 398
 399 int copy_context_skas0(unsigned long new_stack, int pid)
 400 {
 401         struct timeval tv = { .tv_sec = 0, .tv_usec = UM_USEC_PER_SEC / UM_HZ };
 402         int err;
 403         unsigned long current_stack = current_stub_stack();
 404         struct stub_data *data = (struct stub_data *) current_stack;
 405         struct stub_data *child_data = (struct stub_data *) new_stack;
 406         unsigned long long new_offset;
 407         int new_fd = phys_mapping(to_phys((void *)new_stack), &new_offset);
 408
 409         /*
 410          * prepare offset and fd of child's stack as argument for parent's
 411          * and child's mmap2 calls
 412          */
 413         *data = ((struct stub_data) { .offset   = MMAP_OFFSET(new_offset),
 414                                       .fd       = new_fd,
 415                                       .timer    = ((struct itimerval)
 416                                                    { .it_value = tv,
 417                                                      .it_interval = tv }) });
 418
 419         err = ptrace_setregs(pid, thread_regs);
 420         if (err < 0)
 421                 panic("copy_context_skas0 : PTRACE_SETREGS failed, "
 422                       "pid = %d, errno = %d\n", pid, -err);
 423
 424         /* set a well known return code for detection of child write failure */
 425         child_data->err = 12345678;
 426
 427         /*
 428          * Wait, until parent has finished its work: read child's pid from
 429          * parent's stack, and check, if bad result.
 430          */
 431         err = ptrace(PTRACE_CONT, pid, 0, 0);
 432         if (err)
 433                 panic("Failed to continue new process, pid = %d, "
 434                       "errno = %d\n", pid, errno);
 435         wait_stub_done(pid);
 436
 437         pid = data->err;
 438         if (pid < 0)
 439                 panic("copy_context_skas0 - stub-parent reports error %d\n",
 440                       -pid);
 441
 442         /*
 443          * Wait, until child has finished too: read child's result from
 444          * child's stack and check it.
 445          */
 446         wait_stub_done(pid);
 447         if (child_data->err != STUB_DATA)
 448                 panic("copy_context_skas0 - stub-child reports error %ld\n",
 449                       child_data->err);
 450
 451         if (ptrace(PTRACE_OLDSETOPTIONS, pid, NULL,
 452                    (void *)PTRACE_O_TRACESYSGOOD) < 0)
 453                 panic("copy_context_skas0 : PTRACE_OLDSETOPTIONS failed, "
 454                       "errno = %d\n", errno);
 455
 456         return pid;
 457 }
 458
 459 /*
 460  * This is used only, if stub pages are needed, while proc_mm is
 461  * available. Opening /proc/mm creates a new mm_context, which lacks
 462  * the stub-pages. Thus, we map them using /proc/mm-fd
 463  */
 464 void map_stub_pages(int fd, unsigned long code,
 465                     unsigned long data, unsigned long stack)
 466 {
 467         struct proc_mm_op mmop;
 468         int n;
 469         unsigned long long code_offset;
 470         int code_fd = phys_mapping(to_phys((void *) &__syscall_stub_start),
 471                                    &code_offset);
 472
 473         mmop = ((struct proc_mm_op) { .op        = MM_MMAP,
 474                                       .u         =
 475                                       { .mmap    =
 476                                         { .addr    = code,
 477                                           .len     = UM_KERN_PAGE_SIZE,
 478                                           .prot    = PROT_EXEC,
 479                                           .flags   = MAP_FIXED | MAP_PRIVATE,
 480                                           .fd      = code_fd,
 481                                           .offset  = code_offset
 482         } } });
 483         CATCH_EINTR(n = write(fd, &mmop, sizeof(mmop)));
 484         if (n != sizeof(mmop)) {
 485                 n = errno;
 486                 printk(UM_KERN_ERR "mmap args - addr = 0x%lx, fd = %d, "
 487                        "offset = %llx\n", code, code_fd,
 488                        (unsigned long long) code_offset);
 489                 panic("map_stub_pages : /proc/mm map for code failed, "
 490                       "err = %d\n", n);
 491         }
 492
 493         if (stack) {
 494                 unsigned long long map_offset;
 495                 int map_fd = phys_mapping(to_phys((void *)stack), &map_offset);
 496                 mmop = ((struct proc_mm_op)
 497                                 { .op        = MM_MMAP,
 498                                   .u         =
 499                                   { .mmap    =
 500                                     { .addr    = data,
 501                                       .len     = UM_KERN_PAGE_SIZE,
 502                                       .prot    = PROT_READ | PROT_WRITE,
 503                                       .flags   = MAP_FIXED | MAP_SHARED,
 504                                       .fd      = map_fd,
 505                                       .offset  = map_offset
 506                 } } });
 507                 CATCH_EINTR(n = write(fd, &mmop, sizeof(mmop)));
 508                 if (n != sizeof(mmop))
 509                         panic("map_stub_pages : /proc/mm map for data failed, "
 510                               "err = %d\n", errno);
 511         }
 512 }
 513
 514 void new_thread(void *stack, jmp_buf *buf, void (*handler)(void))
 515 {
 516         (*buf)[0].JB_IP = (unsigned long) handler;
 517         (*buf)[0].JB_SP = (unsigned long) stack + UM_THREAD_SIZE -
 518                 sizeof(void *);
 519 }
 520
 521 #define INIT_JMP_NEW_THREAD 0
 522 #define INIT_JMP_CALLBACK 1
 523 #define INIT_JMP_HALT 2
 524 #define INIT_JMP_REBOOT 3
 525
 526 void switch_threads(jmp_buf *me, jmp_buf *you)
 527 {
 528         if (UML_SETJMP(me) == 0)
 529                 UML_LONGJMP(you, 1);
 530 }
 531
 532 static jmp_buf initial_jmpbuf;
 533
 534 /* XXX Make these percpu */
 535 static void (*cb_proc)(void *arg);
 536 static void *cb_arg;
 537 static jmp_buf *cb_back;
 538
 539 int start_idle_thread(void *stack, jmp_buf *switch_buf)
 540 {
 541         int n;
 542
 543         set_handler(SIGWINCH, (__sighandler_t) sig_handler,
 544                     SA_ONSTACK | SA_RESTART, SIGUSR1, SIGIO, SIGVTALRM, -1);
 545
 546         /*
 547          * Can't use UML_SETJMP or UML_LONGJMP here because they save
 548          * and restore signals, with the possible side-effect of
 549          * trying to handle any signals which came when they were
 550          * blocked, which can't be done on this stack.
 551          * Signals must be blocked when jumping back here and restored
 552          * after returning to the jumper.
 553          */
 554         n = setjmp(initial_jmpbuf);
 555         switch(n) {
 556         case INIT_JMP_NEW_THREAD:
 557                 (*switch_buf)[0].JB_IP = (unsigned long) new_thread_handler;
 558                 (*switch_buf)[0].JB_SP = (unsigned long) stack +
 559                         UM_THREAD_SIZE - sizeof(void *);
 560                 break;
 561         case INIT_JMP_CALLBACK:
 562                 (*cb_proc)(cb_arg);
 563                 longjmp(*cb_back, 1);
 564                 break;
 565         case INIT_JMP_HALT:
 566                 kmalloc_ok = 0;
 567                 return 0;
 568         case INIT_JMP_REBOOT:
 569                 kmalloc_ok = 0;
 570                 return 1;
 571         default:
 572                 panic("Bad sigsetjmp return in start_idle_thread - %d\n", n);
 573         }
 574         longjmp(*switch_buf, 1);
 575 }
 576
 577 void initial_thread_cb_skas(void (*proc)(void *), void *arg)
 578 {
 579         jmp_buf here;
 580
 581         cb_proc = proc;
 582         cb_arg = arg;
 583         cb_back = &here;
 584
 585         block_signals();
 586         if (UML_SETJMP(&here) == 0)
 587                 UML_LONGJMP(&initial_jmpbuf, INIT_JMP_CALLBACK);
 588         unblock_signals();
 589
 590         cb_proc = NULL;
 591         cb_arg = NULL;
 592         cb_back = NULL;
 593 }
 594
 595 void halt_skas(void)
 596 {
 597         block_signals();
 598         UML_LONGJMP(&initial_jmpbuf, INIT_JMP_HALT);
 599 }
 600
 601 void reboot_skas(void)
 602 {
 603         block_signals();
 604         UML_LONGJMP(&initial_jmpbuf, INIT_JMP_REBOOT);
 605 }
 606
 607 void __switch_mm(struct mm_id *mm_idp)
 608 {
 609         int err;
 610
 611         /* FIXME: need cpu pid in __switch_mm */
 612         if (proc_mm) {
 613                 err = ptrace(PTRACE_SWITCH_MM, userspace_pid[0], 0,
 614                              mm_idp->u.mm_fd);
 615                 if (err)
 616                         panic("__switch_mm - PTRACE_SWITCH_MM failed, "
 617                               "errno = %d\n", errno);
 618         }
 619         else userspace_pid[0] = mm_idp->u.pid;
 620 }