sys/kern/sys_process.c

   1 /*
   2  * Copyright (c) 1994, Sean Eric Fagan
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by Sean Eric Fagan.
  16  * 4. The name of the author may not be used to endorse or promote products
  17  *    derived from this software without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  29  * SUCH DAMAGE.
  30  *
  31  * $FreeBSD: src/sys/kern/sys_process.c,v 1.51.2.6 2003/01/08 03:06:45 kan Exp $
  32  * $DragonFly: src/sys/kern/sys_process.c,v 1.30 2007/02/19 01:14:23 corecode Exp $
  33  */
  34
  35 #include <sys/param.h>
  36 #include <sys/systm.h>
  37 #include <sys/sysproto.h>
  38 #include <sys/proc.h>
  39 #include <sys/priv.h>
  40 #include <sys/vnode.h>
  41 #include <sys/ptrace.h>
  42 #include <sys/reg.h>
  43 #include <sys/lock.h>
  44
  45 #include <vm/vm.h>
  46 #include <vm/pmap.h>
  47 #include <vm/vm_map.h>
  48 #include <vm/vm_page.h>
  49
  50 #include <sys/user.h>
  51 #include <vfs/procfs/procfs.h>
  52 #include <sys/thread2.h>
  53
  54 /* use the equivalent procfs code */
  55 #if 0
  56 static int
  57 pread (struct proc *procp, unsigned int addr, unsigned int *retval) {
  58         int             rv;
  59         vm_map_t        map, tmap;
  60         vm_object_t     object;
  61         vm_offset_t     kva = 0;
  62         int             page_offset;    /* offset into page */
  63         vm_offset_t     pageno;         /* page number */
  64         vm_map_entry_t  out_entry;
  65         vm_prot_t       out_prot;
  66         boolean_t       wired;
  67         vm_pindex_t     pindex;
  68
  69         /* Map page into kernel space */
  70
  71         map = &procp->p_vmspace->vm_map;
  72
  73         page_offset = addr - trunc_page(addr);
  74         pageno = trunc_page(addr);
  75
  76         tmap = map;
  77         rv = vm_map_lookup (&tmap, pageno, VM_PROT_READ, &out_entry,
  78                 &object, &pindex, &out_prot, &wired);
  79
  80         if (rv != KERN_SUCCESS)
  81                 return EINVAL;
  82
  83         vm_map_lookup_done (tmap, out_entry, 0);
  84
  85         /* Find space in kernel_map for the page we're interested in */
  86         rv = vm_map_find (&kernel_map, object, IDX_TO_OFF(pindex),
  87                           &kva, PAGE_SIZE,
  88                           0,
  89                           VM_MAPTYPE_NORMAL,
  90                           VM_PROT_ALL, VM_PROT_ALL,
  91                           0);
  92
  93         if (!rv) {
  94                 vm_object_reference (object);
  95
  96                 rv = vm_map_wire (&kernel_map, kva, kva + PAGE_SIZE, 0);
  97                 if (!rv) {
  98                         *retval = 0;
  99                         bcopy ((caddr_t)kva + page_offset,
 100                                retval, sizeof *retval);
 101                 }
 102                 vm_map_remove (&kernel_map, kva, kva + PAGE_SIZE);
 103         }
 104
 105         return rv;
 106 }
 107
 108 static int
 109 pwrite (struct proc *procp, unsigned int addr, unsigned int datum) {
 110         int             rv;
 111         vm_map_t        map, tmap;
 112         vm_object_t     object;
 113         vm_offset_t     kva = 0;
 114         int             page_offset;    /* offset into page */
 115         vm_offset_t     pageno;         /* page number */
 116         vm_map_entry_t  out_entry;
 117         vm_prot_t       out_prot;
 118         boolean_t       wired;
 119         vm_pindex_t     pindex;
 120         boolean_t       fix_prot = 0;
 121
 122         /* Map page into kernel space */
 123
 124         map = &procp->p_vmspace->vm_map;
 125
 126         page_offset = addr - trunc_page(addr);
 127         pageno = trunc_page(addr);
 128
 129         /*
 130          * Check the permissions for the area we're interested in.
 131          */
 132
 133         if (vm_map_check_protection (map, pageno, pageno + PAGE_SIZE,
 134                 VM_PROT_WRITE) == FALSE) {
 135                 /*
 136                  * If the page was not writable, we make it so.
 137                  * XXX It is possible a page may *not* be read/executable,
 138                  * if a process changes that!
 139                  */
 140                 fix_prot = 1;
 141                 /* The page isn't writable, so let's try making it so... */
 142                 if ((rv = vm_map_protect (map, pageno, pageno + PAGE_SIZE,
 143                         VM_PROT_ALL, 0)) != KERN_SUCCESS)
 144                   return EFAULT;        /* I guess... */
 145         }
 146
 147         /*
 148          * Now we need to get the page.  out_entry, out_prot, wired, and
 149          * single_use aren't used.  One would think the vm code would be
 150          * a *bit* nicer...  We use tmap because vm_map_lookup() can
 151          * change the map argument.
 152          */
 153
 154         tmap = map;
 155         rv = vm_map_lookup (&tmap, pageno, VM_PROT_WRITE, &out_entry,
 156                 &object, &pindex, &out_prot, &wired);
 157         if (rv != KERN_SUCCESS) {
 158                 return EINVAL;
 159         }
 160
 161         /*
 162          * Okay, we've got the page.  Let's release tmap.
 163          */
 164
 165         vm_map_lookup_done (tmap, out_entry, 0);
 166
 167         /*
 168          * Fault the page in...
 169          */
 170
 171         rv = vm_fault(map, pageno, VM_PROT_WRITE|VM_PROT_READ, FALSE);
 172         if (rv != KERN_SUCCESS)
 173                 return EFAULT;
 174
 175         /* Find space in kernel_map for the page we're interested in */
 176         rv = vm_map_find (&kernel_map, object, IDX_TO_OFF(pindex),
 177                           &kva, PAGE_SIZE,
 178                           0,
 179                           VM_MAPTYPE_NORMAL,
 180                           VM_PROT_ALL, VM_PROT_ALL,
 181                           0);
 182         if (!rv) {
 183                 vm_object_reference (object);
 184
 185                 rv = vm_map_wire (&kernel_map, kva, kva + PAGE_SIZE, 0);
 186                 if (!rv) {
 187                   bcopy (&datum, (caddr_t)kva + page_offset, sizeof datum);
 188                 }
 189                 vm_map_remove (&kernel_map, kva, kva + PAGE_SIZE);
 190         }
 191
 192         if (fix_prot)
 193                 vm_map_protect (map, pageno, pageno + PAGE_SIZE,
 194                         VM_PROT_READ|VM_PROT_EXECUTE, 0);
 195         return rv;
 196 }
 197 #endif
 198
 199 /*
 200  * Process debugging system call.
 201  */
 202 int
 203 sys_ptrace(struct ptrace_args *uap)
 204 {
 205         struct proc *p = curproc;
 206
 207         /*
 208          * XXX this obfuscation is to reduce stack usage, but the register
 209          * structs may be too large to put on the stack anyway.
 210          */
 211         union {
 212                 struct ptrace_io_desc piod;
 213                 struct dbreg dbreg;
 214                 struct fpreg fpreg;
 215                 struct reg reg;
 216         } r;
 217         void *addr;
 218         int error = 0;
 219
 220         addr = &r;
 221         switch (uap->req) {
 222         case PT_GETREGS:
 223         case PT_GETFPREGS:
 224 #ifdef PT_GETDBREGS
 225         case PT_GETDBREGS:
 226 #endif
 227                 break;
 228         case PT_SETREGS:
 229                 error = copyin(uap->addr, &r.reg, sizeof r.reg);
 230                 break;
 231         case PT_SETFPREGS:
 232                 error = copyin(uap->addr, &r.fpreg, sizeof r.fpreg);
 233                 break;
 234 #ifdef PT_SETDBREGS
 235         case PT_SETDBREGS:
 236                 error = copyin(uap->addr, &r.dbreg, sizeof r.dbreg);
 237                 break;
 238 #endif
 239         case PT_IO:
 240                 error = copyin(uap->addr, &r.piod, sizeof r.piod);
 241                 break;
 242         default:
 243                 addr = uap->addr;
 244         }
 245         if (error)
 246                 return (error);
 247
 248         error = kern_ptrace(p, uap->req, uap->pid, addr, uap->data,
 249                         &uap->sysmsg_result);
 250         if (error)
 251                 return (error);
 252
 253         switch (uap->req) {
 254         case PT_IO:
 255                 (void)copyout(&r.piod, uap->addr, sizeof r.piod);
 256                 break;
 257         case PT_GETREGS:
 258                 error = copyout(&r.reg, uap->addr, sizeof r.reg);
 259                 break;
 260         case PT_GETFPREGS:
 261                 error = copyout(&r.fpreg, uap->addr, sizeof r.fpreg);
 262                 break;
 263 #ifdef PT_GETDBREGS
 264         case PT_GETDBREGS:
 265                 error = copyout(&r.dbreg, uap->addr, sizeof r.dbreg);
 266                 break;
 267 #endif
 268         }
 269
 270         return (error);
 271 }
 272
 273 int
 274 kern_ptrace(struct proc *curp, int req, pid_t pid, void *addr, int data, int *res)
 275 {
 276         struct proc *p, *pp;
 277         struct lwp *lp;
 278         struct iovec iov;
 279         struct uio uio;
 280         struct ptrace_io_desc *piod;
 281         int error = 0;
 282         int write, tmp;
 283
 284         write = 0;
 285         if (req == PT_TRACE_ME) {
 286                 p = curp;
 287         } else {
 288                 if ((p = pfind(pid)) == NULL)
 289                         return ESRCH;
 290         }
 291         if (!PRISON_CHECK(curp->p_ucred, p->p_ucred))
 292                 return (ESRCH);
 293
 294         /* Can't trace a process that's currently exec'ing. */
 295         if ((p->p_flag & P_INEXEC) != 0)
 296                 return EAGAIN;
 297
 298         /*
 299          * Permissions check
 300          */
 301         switch (req) {
 302         case PT_TRACE_ME:
 303                 /* Always legal. */
 304                 break;
 305
 306         case PT_ATTACH:
 307                 /* Self */
 308                 if (p->p_pid == curp->p_pid)
 309                         return EINVAL;
 310
 311                 /* Already traced */
 312                 if (p->p_flag & P_TRACED)
 313                         return EBUSY;
 314
 315                 if (curp->p_flag & P_TRACED)
 316                         for (pp = curp->p_pptr; pp != NULL; pp = pp->p_pptr)
 317                                 if (pp == p)
 318                                         return (EINVAL);
 319
 320                 /* not owned by you, has done setuid (unless you're root) */
 321                 if ((p->p_ucred->cr_ruid != curp->p_ucred->cr_ruid) ||
 322                      (p->p_flag & P_SUGID)) {
 323                         if ((error = priv_check_cred(curp->p_ucred, PRIV_ROOT, 0)) != 0)
 324                                 return error;
 325                 }
 326
 327                 /* can't trace init when securelevel > 0 */
 328                 if (securelevel > 0 && p->p_pid == 1)
 329                         return EPERM;
 330
 331                 /* OK */
 332                 break;
 333
 334         case PT_READ_I:
 335         case PT_READ_D:
 336         case PT_WRITE_I:
 337         case PT_WRITE_D:
 338         case PT_IO:
 339         case PT_CONTINUE:
 340         case PT_KILL:
 341         case PT_STEP:
 342         case PT_DETACH:
 343 #ifdef PT_GETREGS
 344         case PT_GETREGS:
 345 #endif
 346 #ifdef PT_SETREGS
 347         case PT_SETREGS:
 348 #endif
 349 #ifdef PT_GETFPREGS
 350         case PT_GETFPREGS:
 351 #endif
 352 #ifdef PT_SETFPREGS
 353         case PT_SETFPREGS:
 354 #endif
 355 #ifdef PT_GETDBREGS
 356         case PT_GETDBREGS:
 357 #endif
 358 #ifdef PT_SETDBREGS
 359         case PT_SETDBREGS:
 360 #endif
 361                 /* not being traced... */
 362                 if ((p->p_flag & P_TRACED) == 0)
 363                         return EPERM;
 364
 365                 /* not being traced by YOU */
 366                 if (p->p_pptr != curp)
 367                         return EBUSY;
 368
 369                 /* not currently stopped */
 370                 if (p->p_stat != SSTOP ||
 371                     (p->p_flag & P_WAITED) == 0) {
 372                         return EBUSY;
 373                 }
 374
 375                 /* OK */
 376                 break;
 377
 378         default:
 379                 return EINVAL;
 380         }
 381
 382         /* XXX lwp */
 383         lp = FIRST_LWP_IN_PROC(p);
 384 #ifdef FIX_SSTEP
 385         /*
 386          * Single step fixup ala procfs
 387          */
 388         FIX_SSTEP(lp);
 389 #endif
 390
 391         /*
 392          * Actually do the requests
 393          */
 394
 395         *res = 0;
 396
 397         switch (req) {
 398         case PT_TRACE_ME:
 399                 /* set my trace flag and "owner" so it can read/write me */
 400                 p->p_flag |= P_TRACED;
 401                 p->p_oppid = p->p_pptr->p_pid;
 402                 return 0;
 403
 404         case PT_ATTACH:
 405                 /* security check done above */
 406                 p->p_flag |= P_TRACED;
 407                 p->p_oppid = p->p_pptr->p_pid;
 408                 if (p->p_pptr != curp)
 409                         proc_reparent(p, curp);
 410                 data = SIGSTOP;
 411                 goto sendsig;   /* in PT_CONTINUE below */
 412
 413         case PT_STEP:
 414         case PT_CONTINUE:
 415         case PT_DETACH:
 416                 /* Zero means do not send any signal */
 417                 if (data < 0 || data > _SIG_MAXSIG)
 418                         return EINVAL;
 419
 420                 LWPHOLD(lp);
 421
 422                 if (req == PT_STEP) {
 423                         if ((error = ptrace_single_step (lp))) {
 424                                 LWPRELE(lp);
 425                                 return error;
 426                         }
 427                 }
 428
 429                 if (addr != (void *)1) {
 430                         if ((error = ptrace_set_pc (lp,
 431                             (u_long)(uintfptr_t)addr))) {
 432                                 LWPRELE(lp);
 433                                 return error;
 434                         }
 435                 }
 436                 LWPRELE(lp);
 437
 438                 if (req == PT_DETACH) {
 439                         /* reset process parent */
 440                         if (p->p_oppid != p->p_pptr->p_pid) {
 441                                 struct proc *pp;
 442
 443                                 pp = pfind(p->p_oppid);
 444                                 proc_reparent(p, pp ? pp : initproc);
 445                         }
 446
 447                         p->p_flag &= ~(P_TRACED | P_WAITED);
 448                         p->p_oppid = 0;
 449
 450                         /* should we send SIGCHLD? */
 451                 }
 452
 453         sendsig:
 454                 /*
 455                  * Deliver or queue signal.  If the process is stopped
 456                  * force it to be SACTIVE again.
 457                  */
 458                 crit_enter();
 459                 if (p->p_stat == SSTOP) {
 460                         p->p_xstat = data;
 461                         lp->lwp_flag |= LWP_BREAKTSLEEP;
 462                         proc_unstop(p);
 463                 } else if (data) {
 464                         ksignal(p, data);
 465                 }
 466                 crit_exit();
 467                 return 0;
 468
 469         case PT_WRITE_I:
 470         case PT_WRITE_D:
 471                 write = 1;
 472                 /* fallthrough */
 473         case PT_READ_I:
 474         case PT_READ_D:
 475                 /*
 476                  * NOTE! uio_offset represents the offset in the target
 477                  * process.  The iov is in the current process (the guy
 478                  * making the ptrace call) so uio_td must be the current
 479                  * process (though for a SYSSPACE transfer it doesn't
 480                  * really matter).
 481                  */
 482                 tmp = 0;
 483                 /* write = 0 set above */
 484                 iov.iov_base = write ? (caddr_t)&data : (caddr_t)&tmp;
 485                 iov.iov_len = sizeof(int);
 486                 uio.uio_iov = &iov;
 487                 uio.uio_iovcnt = 1;
 488                 uio.uio_offset = (off_t)(uintptr_t)addr;
 489                 uio.uio_resid = sizeof(int);
 490                 uio.uio_segflg = UIO_SYSSPACE;
 491                 uio.uio_rw = write ? UIO_WRITE : UIO_READ;
 492                 uio.uio_td = curthread;
 493                 error = procfs_domem(curp, lp, NULL, &uio);
 494                 if (uio.uio_resid != 0) {
 495                         /*
 496                          * XXX procfs_domem() doesn't currently return ENOSPC,
 497                          * so I think write() can bogusly return 0.
 498                          * XXX what happens for short writes?  We don't want
 499                          * to write partial data.
 500                          * XXX procfs_domem() returns EPERM for other invalid
 501                          * addresses.  Convert this to EINVAL.  Does this
 502                          * clobber returns of EPERM for other reasons?
 503                          */
 504                         if (error == 0 || error == ENOSPC || error == EPERM)
 505                                 error = EINVAL; /* EOF */
 506                 }
 507                 if (!write)
 508                         *res = tmp;
 509                 return (error);
 510
 511         case PT_IO:
 512                 /*
 513                  * NOTE! uio_offset represents the offset in the target
 514                  * process.  The iov is in the current process (the guy
 515                  * making the ptrace call) so uio_td must be the current
 516                  * process.
 517                  */
 518                 piod = addr;
 519                 iov.iov_base = piod->piod_addr;
 520                 iov.iov_len = piod->piod_len;
 521                 uio.uio_iov = &iov;
 522                 uio.uio_iovcnt = 1;
 523                 uio.uio_offset = (off_t)(uintptr_t)piod->piod_offs;
 524                 uio.uio_resid = piod->piod_len;
 525                 uio.uio_segflg = UIO_USERSPACE;
 526                 uio.uio_td = curthread;
 527                 switch (piod->piod_op) {
 528                 case PIOD_READ_D:
 529                 case PIOD_READ_I:
 530                         uio.uio_rw = UIO_READ;
 531                         break;
 532                 case PIOD_WRITE_D:
 533                 case PIOD_WRITE_I:
 534                         uio.uio_rw = UIO_WRITE;
 535                         break;
 536                 default:
 537                         return (EINVAL);
 538                 }
 539                 error = procfs_domem(curp, lp, NULL, &uio);
 540                 piod->piod_len -= uio.uio_resid;
 541                 return (error);
 542
 543         case PT_KILL:
 544                 data = SIGKILL;
 545                 goto sendsig;   /* in PT_CONTINUE above */
 546
 547 #ifdef PT_SETREGS
 548         case PT_SETREGS:
 549                 write = 1;
 550                 /* fallthrough */
 551 #endif /* PT_SETREGS */
 552 #ifdef PT_GETREGS
 553         case PT_GETREGS:
 554                 /* write = 0 above */
 555 #endif /* PT_SETREGS */
 556 #if defined(PT_SETREGS) || defined(PT_GETREGS)
 557                 if (!procfs_validregs(lp))      /* no P_SYSTEM procs please */
 558                         return EINVAL;
 559                 else {
 560                         iov.iov_base = addr;
 561                         iov.iov_len = sizeof(struct reg);
 562                         uio.uio_iov = &iov;
 563                         uio.uio_iovcnt = 1;
 564                         uio.uio_offset = 0;
 565                         uio.uio_resid = sizeof(struct reg);
 566                         uio.uio_segflg = UIO_SYSSPACE;
 567                         uio.uio_rw = write ? UIO_WRITE : UIO_READ;
 568                         uio.uio_td = curthread;
 569                         return (procfs_doregs(curp, lp, NULL, &uio));
 570                 }
 571 #endif /* defined(PT_SETREGS) || defined(PT_GETREGS) */
 572
 573 #ifdef PT_SETFPREGS
 574         case PT_SETFPREGS:
 575                 write = 1;
 576                 /* fallthrough */
 577 #endif /* PT_SETFPREGS */
 578 #ifdef PT_GETFPREGS
 579         case PT_GETFPREGS:
 580                 /* write = 0 above */
 581 #endif /* PT_SETFPREGS */
 582 #if defined(PT_SETFPREGS) || defined(PT_GETFPREGS)
 583                 if (!procfs_validfpregs(lp))    /* no P_SYSTEM procs please */
 584                         return EINVAL;
 585                 else {
 586                         iov.iov_base = addr;
 587                         iov.iov_len = sizeof(struct fpreg);
 588                         uio.uio_iov = &iov;
 589                         uio.uio_iovcnt = 1;
 590                         uio.uio_offset = 0;
 591                         uio.uio_resid = sizeof(struct fpreg);
 592                         uio.uio_segflg = UIO_SYSSPACE;
 593                         uio.uio_rw = write ? UIO_WRITE : UIO_READ;
 594                         uio.uio_td = curthread;
 595                         return (procfs_dofpregs(curp, lp, NULL, &uio));
 596                 }
 597 #endif /* defined(PT_SETFPREGS) || defined(PT_GETFPREGS) */
 598
 599 #ifdef PT_SETDBREGS
 600         case PT_SETDBREGS:
 601                 write = 1;
 602                 /* fallthrough */
 603 #endif /* PT_SETDBREGS */
 604 #ifdef PT_GETDBREGS
 605         case PT_GETDBREGS:
 606                 /* write = 0 above */
 607 #endif /* PT_SETDBREGS */
 608 #if defined(PT_SETDBREGS) || defined(PT_GETDBREGS)
 609                 if (!procfs_validdbregs(lp))    /* no P_SYSTEM procs please */
 610                         return EINVAL;
 611                 else {
 612                         iov.iov_base = addr;
 613                         iov.iov_len = sizeof(struct dbreg);
 614                         uio.uio_iov = &iov;
 615                         uio.uio_iovcnt = 1;
 616                         uio.uio_offset = 0;
 617                         uio.uio_resid = sizeof(struct dbreg);
 618                         uio.uio_segflg = UIO_SYSSPACE;
 619                         uio.uio_rw = write ? UIO_WRITE : UIO_READ;
 620                         uio.uio_td = curthread;
 621                         return (procfs_dodbregs(curp, lp, NULL, &uio));
 622                 }
 623 #endif /* defined(PT_SETDBREGS) || defined(PT_GETDBREGS) */
 624
 625         default:
 626                 break;
 627         }
 628
 629         return 0;
 630 }
 631
 632 int
 633 trace_req(struct proc *p)
 634 {
 635         return 1;
 636 }
 637
 638 /*
 639  * stopevent()
 640  *
 641  * Stop a process because of a procfs event.  Stay stopped until p->p_step
 642  * is cleared (cleared by PIOCCONT in procfs).
 643  *
 644  * MPSAFE
 645  */
 646 void
 647 stopevent(struct proc *p, unsigned int event, unsigned int val)
 648 {
 649         p->p_step = 1;
 650
 651         do {
 652                 crit_enter();
 653                 wakeup(&p->p_stype);    /* Wake up any PIOCWAIT'ing procs */
 654                 p->p_xstat = val;
 655                 p->p_stype = event;     /* Which event caused the stop? */
 656                 tsleep(&p->p_step, 0, "stopevent", 0);
 657                 crit_exit();
 658         } while (p->p_step);
 659 }
 660