1 /* $NetBSD: kern_fork.c,v 1.66 2000/05/31 05:02:32 thorpej Exp $ */ 2 3 /* 4 * Copyright (c) 1982, 1986, 1989, 1991, 1993 5 * The Regents of the University of California. All rights reserved. 6 * (c) UNIX System Laboratories, Inc. 7 * All or some portions of this file are derived from material licensed 8 * to the University of California by American Telephone and Telegraph 9 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 10 * the permission of UNIX System Laboratories, Inc. 11 * 12 * Redistribution and use in source and binary forms, with or without 13 * modification, are permitted provided that the following conditions 14 * are met: 15 * 1. Redistributions of source code must retain the above copyright 16 * notice, this list of conditions and the following disclaimer. 17 * 2. Redistributions in binary form must reproduce the above copyright 18 * notice, this list of conditions and the following disclaimer in the 19 * documentation and/or other materials provided with the distribution. 20 * 3. All advertising materials mentioning features or use of this software 21 * must display the following acknowledgement: 22 * This product includes software developed by the University of 23 * California, Berkeley and its contributors. 24 * 4. Neither the name of the University nor the names of its contributors 25 * may be used to endorse or promote products derived from this software 26 * without specific prior written permission. 27 * 28 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 29 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 30 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 31 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 32 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 33 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 34 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 35 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 37 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 38 * SUCH DAMAGE. 39 * 40 * @(#)kern_fork.c 8.8 (Berkeley) 2/14/95 41 */ 42 43 #include "opt_ktrace.h" 44 #include "opt_multiprocessor.h" 45 46 #include <sys/param.h> 47 #include <sys/systm.h> 48 #include <sys/map.h> 49 #include <sys/filedesc.h> 50 #include <sys/kernel.h> 51 #include <sys/malloc.h> 52 #include <sys/pool.h> 53 #include <sys/mount.h> 54 #include <sys/proc.h> 55 #include <sys/resourcevar.h> 56 #include <sys/vnode.h> 57 #include <sys/file.h> 58 #include <sys/acct.h> 59 #include <sys/ktrace.h> 60 #include <sys/vmmeter.h> 61 #include <sys/sched.h> 62 #include <sys/signalvar.h> 63 64 #include <sys/syscallargs.h> 65 66 #include <vm/vm.h> 67 #include <vm/vm_kern.h> 68 69 #include <uvm/uvm_extern.h> 70 71 int nprocs = 1; /* process 0 */ 72 73 /*ARGSUSED*/ 74 int 75 sys_fork(p, v, retval) 76 struct proc *p; 77 void *v; 78 register_t *retval; 79 { 80 81 return (fork1(p, 0, SIGCHLD, NULL, 0, NULL, NULL, retval, NULL)); 82 } 83 84 /* 85 * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM). 86 * Address space is not shared, but parent is blocked until child exit. 87 */ 88 /*ARGSUSED*/ 89 int 90 sys_vfork(p, v, retval) 91 struct proc *p; 92 void *v; 93 register_t *retval; 94 { 95 96 return (fork1(p, FORK_PPWAIT, SIGCHLD, NULL, 0, NULL, NULL, 97 retval, NULL)); 98 } 99 100 /* 101 * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2) 102 * semantics. Address space is shared, and parent is blocked until child exit. 103 */ 104 /*ARGSUSED*/ 105 int 106 sys___vfork14(p, v, retval) 107 struct proc *p; 108 void *v; 109 register_t *retval; 110 { 111 112 return (fork1(p, FORK_PPWAIT|FORK_SHAREVM, SIGCHLD, NULL, 0, 113 NULL, NULL, retval, NULL)); 114 } 115 116 int 117 fork1(p1, flags, exitsig, stack, stacksize, func, arg, retval, rnewprocp) 118 struct proc *p1; 119 int flags; 120 int exitsig; 121 void *stack; 122 size_t stacksize; 123 void (*func) __P((void *)); 124 void *arg; 125 register_t *retval; 126 struct proc **rnewprocp; 127 { 128 struct proc *p2; 129 uid_t uid; 130 struct proc *newproc; 131 int count, s; 132 vaddr_t uaddr; 133 static int nextpid, pidchecked = 0; 134 135 /* 136 * Although process entries are dynamically created, we still keep 137 * a global limit on the maximum number we will create. Don't allow 138 * a nonprivileged user to use the last process; don't let root 139 * exceed the limit. The variable nprocs is the current number of 140 * processes, maxproc is the limit. 141 */ 142 uid = p1->p_cred->p_ruid; 143 if (__predict_false((nprocs >= maxproc - 1 && uid != 0) || 144 nprocs >= maxproc)) { 145 tablefull("proc"); 146 return (EAGAIN); 147 } 148 149 /* 150 * Increment the count of procs running with this uid. Don't allow 151 * a nonprivileged user to exceed their current limit. 152 */ 153 count = chgproccnt(uid, 1); 154 if (__predict_false(uid != 0 && count > 155 p1->p_rlimit[RLIMIT_NPROC].rlim_cur)) { 156 (void)chgproccnt(uid, -1); 157 return (EAGAIN); 158 } 159 160 /* 161 * Allocate virtual address space for the U-area now, while it 162 * is still easy to abort the fork operation if we're out of 163 * kernel virtual address space. The actual U-area pages will 164 * be allocated and wired in vm_fork(). 165 */ 166 uaddr = uvm_km_valloc(kernel_map, USPACE); 167 if (__predict_false(uaddr == 0)) { 168 (void)chgproccnt(uid, -1); 169 return (ENOMEM); 170 } 171 172 /* 173 * We are now committed to the fork. From here on, we may 174 * block on resources, but resource allocation may NOT fail. 175 */ 176 177 /* Allocate new proc. */ 178 newproc = pool_get(&proc_pool, PR_WAITOK); 179 180 /* 181 * BEGIN PID ALLOCATION. 182 */ 183 s = proclist_lock_write(); 184 185 /* 186 * Find an unused process ID. We remember a range of unused IDs 187 * ready to use (from nextpid+1 through pidchecked-1). 188 */ 189 nextpid++; 190 retry: 191 /* 192 * If the process ID prototype has wrapped around, 193 * restart somewhat above 0, as the low-numbered procs 194 * tend to include daemons that don't exit. 195 */ 196 if (nextpid >= PID_MAX) { 197 nextpid = 100; 198 pidchecked = 0; 199 } 200 if (nextpid >= pidchecked) { 201 const struct proclist_desc *pd; 202 203 pidchecked = PID_MAX; 204 /* 205 * Scan the process lists to check whether this pid 206 * is in use. Remember the lowest pid that's greater 207 * than nextpid, so we can avoid checking for a while. 208 */ 209 pd = proclists; 210 again: 211 for (p2 = LIST_FIRST(pd->pd_list); p2 != 0; 212 p2 = LIST_NEXT(p2, p_list)) { 213 while (p2->p_pid == nextpid || 214 p2->p_pgrp->pg_id == nextpid || 215 p2->p_session->s_sid == nextpid) { 216 nextpid++; 217 if (nextpid >= pidchecked) 218 goto retry; 219 } 220 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 221 pidchecked = p2->p_pid; 222 223 if (p2->p_pgrp->pg_id > nextpid && 224 pidchecked > p2->p_pgrp->pg_id) 225 pidchecked = p2->p_pgrp->pg_id; 226 227 if (p2->p_session->s_sid > nextpid && 228 pidchecked > p2->p_session->s_sid) 229 pidchecked = p2->p_session->s_sid; 230 } 231 232 /* 233 * If there's another list, scan it. If we have checked 234 * them all, we've found one! 235 */ 236 pd++; 237 if (pd->pd_list != NULL) 238 goto again; 239 } 240 241 nprocs++; 242 p2 = newproc; 243 244 /* Record the pid we've allocated. */ 245 p2->p_pid = nextpid; 246 247 /* Record the signal to be delivered to the parent on exit. */ 248 p2->p_exitsig = exitsig; 249 250 /* 251 * Put the proc on allproc before unlocking PID allocation 252 * so that waiters won't grab it as soon as we unlock. 253 */ 254 255 p2->p_stat = SIDL; /* protect against others */ 256 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */ 257 258 LIST_INSERT_HEAD(&allproc, p2, p_list); 259 260 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash); 261 262 /* 263 * END PID ALLOCATION. 264 */ 265 proclist_unlock_write(s); 266 267 /* 268 * Make a proc table entry for the new process. 269 * Start by zeroing the section of proc that is zero-initialized, 270 * then copy the section that is copied directly from the parent. 271 */ 272 memset(&p2->p_startzero, 0, 273 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 274 memcpy(&p2->p_startcopy, &p1->p_startcopy, 275 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 276 277 #if !defined(MULTIPROCESSOR) 278 /* 279 * In the single-processor case, all processes will always run 280 * on the same CPU. So, initialize the child's CPU to the parent's 281 * now. In the multiprocessor case, the child's CPU will be 282 * initialized in the low-level context switch code when the 283 * process runs. 284 */ 285 p2->p_cpu = p1->p_cpu; 286 #endif /* ! MULTIPROCESSOR */ 287 288 /* 289 * Duplicate sub-structures as needed. 290 * Increase reference counts on shared objects. 291 * The p_stats and p_sigacts substructs are set in vm_fork. 292 */ 293 p2->p_flag = P_INMEM | (p1->p_flag & P_SUGID); 294 p2->p_emul = p1->p_emul; 295 if (p1->p_flag & P_PROFIL) 296 startprofclock(p2); 297 p2->p_cred = pool_get(&pcred_pool, PR_WAITOK); 298 memcpy(p2->p_cred, p1->p_cred, sizeof(*p2->p_cred)); 299 p2->p_cred->p_refcnt = 1; 300 crhold(p1->p_ucred); 301 302 /* bump references to the text vnode (for procfs) */ 303 p2->p_textvp = p1->p_textvp; 304 if (p2->p_textvp) 305 VREF(p2->p_textvp); 306 307 if (flags & FORK_SHAREFILES) 308 fdshare(p1, p2); 309 else 310 p2->p_fd = fdcopy(p1); 311 312 if (flags & FORK_SHARECWD) 313 cwdshare(p1, p2); 314 else 315 p2->p_cwdi = cwdinit(p1); 316 317 /* 318 * If p_limit is still copy-on-write, bump refcnt, 319 * otherwise get a copy that won't be modified. 320 * (If PL_SHAREMOD is clear, the structure is shared 321 * copy-on-write.) 322 */ 323 if (p1->p_limit->p_lflags & PL_SHAREMOD) 324 p2->p_limit = limcopy(p1->p_limit); 325 else { 326 p2->p_limit = p1->p_limit; 327 p2->p_limit->p_refcnt++; 328 } 329 330 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 331 p2->p_flag |= P_CONTROLT; 332 if (flags & FORK_PPWAIT) 333 p2->p_flag |= P_PPWAIT; 334 LIST_INSERT_AFTER(p1, p2, p_pglist); 335 p2->p_pptr = p1; 336 LIST_INSERT_HEAD(&p1->p_children, p2, p_sibling); 337 LIST_INIT(&p2->p_children); 338 339 callout_init(&p2->p_realit_ch); 340 callout_init(&p2->p_tsleep_ch); 341 342 #ifdef KTRACE 343 /* 344 * Copy traceflag and tracefile if enabled. 345 * If not inherited, these were zeroed above. 346 */ 347 if (p1->p_traceflag&KTRFAC_INHERIT) { 348 p2->p_traceflag = p1->p_traceflag; 349 if ((p2->p_tracep = p1->p_tracep) != NULL) 350 ktradref(p2); 351 } 352 #endif 353 scheduler_fork_hook(p1, p2); 354 355 /* 356 * Create signal actions for the child process. 357 */ 358 if (flags & FORK_SHARESIGS) 359 sigactsshare(p1, p2); 360 else 361 p2->p_sigacts = sigactsinit(p1); 362 363 /* 364 * This begins the section where we must prevent the parent 365 * from being swapped. 366 */ 367 PHOLD(p1); 368 369 /* 370 * Finish creating the child process. It will return through a 371 * different path later. 372 */ 373 p2->p_addr = (struct user *)uaddr; 374 uvm_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE, 375 stack, stacksize, 376 (func != NULL) ? func : child_return, 377 (arg != NULL) ? arg : p2); 378 379 /* 380 * Make child runnable, set start time, and add to run queue. 381 */ 382 s = splstatclock(); 383 p2->p_stats->p_start = time; 384 p2->p_acflag = AFORK; 385 p2->p_stat = SRUN; 386 setrunqueue(p2); 387 splx(s); 388 389 /* 390 * Now can be swapped. 391 */ 392 PRELE(p1); 393 394 /* 395 * Update stats now that we know the fork was successful. 396 */ 397 uvmexp.forks++; 398 if (flags & FORK_PPWAIT) 399 uvmexp.forks_ppwait++; 400 if (flags & FORK_SHAREVM) 401 uvmexp.forks_sharevm++; 402 403 /* 404 * Pass a pointer to the new process to the caller. 405 */ 406 if (rnewprocp != NULL) 407 *rnewprocp = p2; 408 409 /* 410 * Preserve synchronization semantics of vfork. If waiting for 411 * child to exec or exit, set P_PPWAIT on child, and sleep on our 412 * proc (in case of exit). 413 */ 414 if (flags & FORK_PPWAIT) 415 while (p2->p_flag & P_PPWAIT) 416 tsleep(p1, PWAIT, "ppwait", 0); 417 418 /* 419 * Return child pid to parent process, 420 * marking us as parent via retval[1]. 421 */ 422 if (retval != NULL) { 423 retval[0] = p2->p_pid; 424 retval[1] = 0; 425 } 426 return (0); 427 } 428