1 /* $NetBSD: kern_fork.c,v 1.69 2000/07/04 15:33:30 jdolecek 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 <uvm/uvm_extern.h> 67 68 int nprocs = 1; /* process 0 */ 69 70 /*ARGSUSED*/ 71 int 72 sys_fork(p, v, retval) 73 struct proc *p; 74 void *v; 75 register_t *retval; 76 { 77 78 return (fork1(p, 0, SIGCHLD, NULL, 0, NULL, NULL, retval, NULL)); 79 } 80 81 /* 82 * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM). 83 * Address space is not shared, but parent is blocked until child exit. 84 */ 85 /*ARGSUSED*/ 86 int 87 sys_vfork(p, v, retval) 88 struct proc *p; 89 void *v; 90 register_t *retval; 91 { 92 93 return (fork1(p, FORK_PPWAIT, SIGCHLD, NULL, 0, NULL, NULL, 94 retval, NULL)); 95 } 96 97 /* 98 * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2) 99 * semantics. Address space is shared, and parent is blocked until child exit. 100 */ 101 /*ARGSUSED*/ 102 int 103 sys___vfork14(p, v, retval) 104 struct proc *p; 105 void *v; 106 register_t *retval; 107 { 108 109 return (fork1(p, FORK_PPWAIT|FORK_SHAREVM, SIGCHLD, NULL, 0, 110 NULL, NULL, retval, NULL)); 111 } 112 113 int 114 fork1(p1, flags, exitsig, stack, stacksize, func, arg, retval, rnewprocp) 115 struct proc *p1; 116 int flags; 117 int exitsig; 118 void *stack; 119 size_t stacksize; 120 void (*func) __P((void *)); 121 void *arg; 122 register_t *retval; 123 struct proc **rnewprocp; 124 { 125 struct proc *p2; 126 uid_t uid; 127 struct proc *newproc; 128 int count, s; 129 vaddr_t uaddr; 130 static int nextpid, pidchecked = 0; 131 132 /* 133 * Although process entries are dynamically created, we still keep 134 * a global limit on the maximum number we will create. Don't allow 135 * a nonprivileged user to use the last process; don't let root 136 * exceed the limit. The variable nprocs is the current number of 137 * processes, maxproc is the limit. 138 */ 139 uid = p1->p_cred->p_ruid; 140 if (__predict_false((nprocs >= maxproc - 1 && uid != 0) || 141 nprocs >= maxproc)) { 142 tablefull("proc", "increase kern.maxproc or NPROC"); 143 return (EAGAIN); 144 } 145 146 /* 147 * Increment the count of procs running with this uid. Don't allow 148 * a nonprivileged user to exceed their current limit. 149 */ 150 count = chgproccnt(uid, 1); 151 if (__predict_false(uid != 0 && count > 152 p1->p_rlimit[RLIMIT_NPROC].rlim_cur)) { 153 (void)chgproccnt(uid, -1); 154 return (EAGAIN); 155 } 156 157 /* 158 * Allocate virtual address space for the U-area now, while it 159 * is still easy to abort the fork operation if we're out of 160 * kernel virtual address space. The actual U-area pages will 161 * be allocated and wired in vm_fork(). 162 */ 163 uaddr = uvm_km_valloc(kernel_map, USPACE); 164 if (__predict_false(uaddr == 0)) { 165 (void)chgproccnt(uid, -1); 166 return (ENOMEM); 167 } 168 169 /* 170 * We are now committed to the fork. From here on, we may 171 * block on resources, but resource allocation may NOT fail. 172 */ 173 174 /* Allocate new proc. */ 175 newproc = pool_get(&proc_pool, PR_WAITOK); 176 177 /* 178 * BEGIN PID ALLOCATION. 179 */ 180 s = proclist_lock_write(); 181 182 /* 183 * Find an unused process ID. We remember a range of unused IDs 184 * ready to use (from nextpid+1 through pidchecked-1). 185 */ 186 nextpid++; 187 retry: 188 /* 189 * If the process ID prototype has wrapped around, 190 * restart somewhat above 0, as the low-numbered procs 191 * tend to include daemons that don't exit. 192 */ 193 if (nextpid >= PID_MAX) { 194 nextpid = 100; 195 pidchecked = 0; 196 } 197 if (nextpid >= pidchecked) { 198 const struct proclist_desc *pd; 199 200 pidchecked = PID_MAX; 201 /* 202 * Scan the process lists to check whether this pid 203 * is in use. Remember the lowest pid that's greater 204 * than nextpid, so we can avoid checking for a while. 205 */ 206 pd = proclists; 207 again: 208 for (p2 = LIST_FIRST(pd->pd_list); p2 != 0; 209 p2 = LIST_NEXT(p2, p_list)) { 210 while (p2->p_pid == nextpid || 211 p2->p_pgrp->pg_id == nextpid || 212 p2->p_session->s_sid == nextpid) { 213 nextpid++; 214 if (nextpid >= pidchecked) 215 goto retry; 216 } 217 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 218 pidchecked = p2->p_pid; 219 220 if (p2->p_pgrp->pg_id > nextpid && 221 pidchecked > p2->p_pgrp->pg_id) 222 pidchecked = p2->p_pgrp->pg_id; 223 224 if (p2->p_session->s_sid > nextpid && 225 pidchecked > p2->p_session->s_sid) 226 pidchecked = p2->p_session->s_sid; 227 } 228 229 /* 230 * If there's another list, scan it. If we have checked 231 * them all, we've found one! 232 */ 233 pd++; 234 if (pd->pd_list != NULL) 235 goto again; 236 } 237 238 nprocs++; 239 p2 = newproc; 240 241 /* Record the pid we've allocated. */ 242 p2->p_pid = nextpid; 243 244 /* Record the signal to be delivered to the parent on exit. */ 245 p2->p_exitsig = exitsig; 246 247 /* 248 * Put the proc on allproc before unlocking PID allocation 249 * so that waiters won't grab it as soon as we unlock. 250 */ 251 252 p2->p_stat = SIDL; /* protect against others */ 253 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */ 254 255 LIST_INSERT_HEAD(&allproc, p2, p_list); 256 257 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash); 258 259 /* 260 * END PID ALLOCATION. 261 */ 262 proclist_unlock_write(s); 263 264 /* 265 * Make a proc table entry for the new process. 266 * Start by zeroing the section of proc that is zero-initialized, 267 * then copy the section that is copied directly from the parent. 268 */ 269 memset(&p2->p_startzero, 0, 270 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 271 memcpy(&p2->p_startcopy, &p1->p_startcopy, 272 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 273 274 #if !defined(MULTIPROCESSOR) 275 /* 276 * In the single-processor case, all processes will always run 277 * on the same CPU. So, initialize the child's CPU to the parent's 278 * now. In the multiprocessor case, the child's CPU will be 279 * initialized in the low-level context switch code when the 280 * process runs. 281 */ 282 p2->p_cpu = p1->p_cpu; 283 #endif /* ! MULTIPROCESSOR */ 284 285 /* 286 * Duplicate sub-structures as needed. 287 * Increase reference counts on shared objects. 288 * The p_stats and p_sigacts substructs are set in vm_fork. 289 */ 290 p2->p_flag = P_INMEM | (p1->p_flag & P_SUGID); 291 p2->p_emul = p1->p_emul; 292 if (p1->p_flag & P_PROFIL) 293 startprofclock(p2); 294 p2->p_cred = pool_get(&pcred_pool, PR_WAITOK); 295 memcpy(p2->p_cred, p1->p_cred, sizeof(*p2->p_cred)); 296 p2->p_cred->p_refcnt = 1; 297 crhold(p1->p_ucred); 298 299 /* bump references to the text vnode (for procfs) */ 300 p2->p_textvp = p1->p_textvp; 301 if (p2->p_textvp) 302 VREF(p2->p_textvp); 303 304 if (flags & FORK_SHAREFILES) 305 fdshare(p1, p2); 306 else 307 p2->p_fd = fdcopy(p1); 308 309 if (flags & FORK_SHARECWD) 310 cwdshare(p1, p2); 311 else 312 p2->p_cwdi = cwdinit(p1); 313 314 /* 315 * If p_limit is still copy-on-write, bump refcnt, 316 * otherwise get a copy that won't be modified. 317 * (If PL_SHAREMOD is clear, the structure is shared 318 * copy-on-write.) 319 */ 320 if (p1->p_limit->p_lflags & PL_SHAREMOD) 321 p2->p_limit = limcopy(p1->p_limit); 322 else { 323 p2->p_limit = p1->p_limit; 324 p2->p_limit->p_refcnt++; 325 } 326 327 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 328 p2->p_flag |= P_CONTROLT; 329 if (flags & FORK_PPWAIT) 330 p2->p_flag |= P_PPWAIT; 331 LIST_INSERT_AFTER(p1, p2, p_pglist); 332 p2->p_pptr = p1; 333 LIST_INSERT_HEAD(&p1->p_children, p2, p_sibling); 334 LIST_INIT(&p2->p_children); 335 336 callout_init(&p2->p_realit_ch); 337 callout_init(&p2->p_tsleep_ch); 338 339 #ifdef KTRACE 340 /* 341 * Copy traceflag and tracefile if enabled. 342 * If not inherited, these were zeroed above. 343 */ 344 if (p1->p_traceflag&KTRFAC_INHERIT) { 345 p2->p_traceflag = p1->p_traceflag; 346 if ((p2->p_tracep = p1->p_tracep) != NULL) 347 ktradref(p2); 348 } 349 #endif 350 scheduler_fork_hook(p1, p2); 351 352 /* 353 * Create signal actions for the child process. 354 */ 355 if (flags & FORK_SHARESIGS) 356 sigactsshare(p1, p2); 357 else 358 p2->p_sigacts = sigactsinit(p1); 359 360 /* 361 * This begins the section where we must prevent the parent 362 * from being swapped. 363 */ 364 PHOLD(p1); 365 366 /* 367 * Finish creating the child process. It will return through a 368 * different path later. 369 */ 370 p2->p_addr = (struct user *)uaddr; 371 uvm_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE, 372 stack, stacksize, 373 (func != NULL) ? func : child_return, 374 (arg != NULL) ? arg : p2); 375 376 /* 377 * Make child runnable, set start time, and add to run queue. 378 */ 379 s = splstatclock(); 380 p2->p_stats->p_start = time; 381 p2->p_acflag = AFORK; 382 p2->p_stat = SRUN; 383 setrunqueue(p2); 384 splx(s); 385 386 /* 387 * Now can be swapped. 388 */ 389 PRELE(p1); 390 391 /* 392 * Update stats now that we know the fork was successful. 393 */ 394 uvmexp.forks++; 395 if (flags & FORK_PPWAIT) 396 uvmexp.forks_ppwait++; 397 if (flags & FORK_SHAREVM) 398 uvmexp.forks_sharevm++; 399 400 /* 401 * Pass a pointer to the new process to the caller. 402 */ 403 if (rnewprocp != NULL) 404 *rnewprocp = p2; 405 406 /* 407 * Preserve synchronization semantics of vfork. If waiting for 408 * child to exec or exit, set P_PPWAIT on child, and sleep on our 409 * proc (in case of exit). 410 */ 411 if (flags & FORK_PPWAIT) 412 while (p2->p_flag & P_PPWAIT) 413 tsleep(p1, PWAIT, "ppwait", 0); 414 415 /* 416 * Return child pid to parent process, 417 * marking us as parent via retval[1]. 418 */ 419 if (retval != NULL) { 420 retval[0] = p2->p_pid; 421 retval[1] = 0; 422 } 423 return (0); 424 } 425