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38 * @(#)kern_fork.c 8.6 (Berkeley) 4/8/94
39 * $FreeBSD: src/sys/kern/kern_fork.c,v 1.72.2.14 2003/06/26 04:15:10 silby Exp $
40 * $DragonFly: src/sys/kern/kern_fork.c,v 1.44 2005/11/14 18:50:05 dillon Exp $
43 #include "opt_ktrace.h"
45 #include <sys/param.h>
46 #include <sys/systm.h>
47 #include <sys/sysproto.h>
48 #include <sys/filedesc.h>
49 #include <sys/kernel.h>
50 #include <sys/sysctl.h>
51 #include <sys/malloc.h>
53 #include <sys/resourcevar.h>
54 #include <sys/vnode.h>
56 #include <sys/ktrace.h>
57 #include <sys/unistd.h>
64 #include <vm/vm_map.h>
65 #include <vm/vm_extern.h>
66 #include <vm/vm_zone.h>
68 #include <sys/vmmeter.h>
70 #include <sys/thread2.h>
72 static MALLOC_DEFINE(M_ATFORK
, "atfork", "atfork callback");
75 * These are the stuctures used to create a callout list for things to do
76 * when forking a process
80 TAILQ_ENTRY(forklist
) next
;
83 TAILQ_HEAD(forklist_head
, forklist
);
84 static struct forklist_head fork_list
= TAILQ_HEAD_INITIALIZER(fork_list
);
86 int forksleep
; /* Place for fork1() to sleep on. */
90 fork(struct fork_args
*uap
)
92 struct lwp
*lp
= curthread
->td_lwp
;
96 error
= fork1(lp
, RFFDG
| RFPROC
, &p2
);
98 start_forked_proc(lp
, p2
);
99 uap
->sysmsg_fds
[0] = p2
->p_pid
;
100 uap
->sysmsg_fds
[1] = 0;
107 vfork(struct vfork_args
*uap
)
109 struct lwp
*lp
= curthread
->td_lwp
;
113 error
= fork1(lp
, RFFDG
| RFPROC
| RFPPWAIT
| RFMEM
, &p2
);
115 start_forked_proc(lp
, p2
);
116 uap
->sysmsg_fds
[0] = p2
->p_pid
;
117 uap
->sysmsg_fds
[1] = 0;
123 * Handle rforks. An rfork may (1) operate on the current process without
124 * creating a new, (2) create a new process that shared the current process's
125 * vmspace, signals, and/or descriptors, or (3) create a new process that does
126 * not share these things (normal fork).
128 * Note that we only call start_forked_proc() if a new process is actually
131 * rfork { int flags }
134 rfork(struct rfork_args
*uap
)
136 struct lwp
*lp
= curthread
->td_lwp
;
140 if ((uap
->flags
& RFKERNELONLY
) != 0)
143 error
= fork1(lp
, uap
->flags
, &p2
);
146 start_forked_proc(lp
, p2
);
147 uap
->sysmsg_fds
[0] = p2
? p2
->p_pid
: 0;
148 uap
->sysmsg_fds
[1] = 0;
154 int nprocs
= 1; /* process 0 */
155 static int nextpid
= 0;
158 * Random component to nextpid generation. We mix in a random factor to make
159 * it a little harder to predict. We sanity check the modulus value to avoid
160 * doing it in critical paths. Don't let it be too small or we pointlessly
161 * waste randomness entropy, and don't let it be impossibly large. Using a
162 * modulus that is too big causes a LOT more process table scans and slows
163 * down fork processing as the pidchecked caching is defeated.
165 static int randompid
= 0;
168 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS
)
173 error
= sysctl_handle_int(oidp
, &pid
, 0, req
);
174 if (error
|| !req
->newptr
)
176 if (pid
< 0 || pid
> PID_MAX
- 100) /* out of range */
178 else if (pid
< 2) /* NOP */
180 else if (pid
< 100) /* Make it reasonable */
186 SYSCTL_PROC(_kern
, OID_AUTO
, randompid
, CTLTYPE_INT
|CTLFLAG_RW
,
187 0, 0, sysctl_kern_randompid
, "I", "Random PID modulus");
190 fork1(struct lwp
*lp1
, int flags
, struct proc
**procp
)
192 struct proc
*p1
= lp1
->lwp_proc
;
193 struct proc
*p2
, *pptr
;
196 struct proc
*newproc
;
198 static int curfail
= 0, pidchecked
= 0;
199 static struct timeval lastfail
;
201 struct filedesc_to_leader
*fdtol
;
203 if ((flags
& (RFFDG
|RFCFDG
)) == (RFFDG
|RFCFDG
))
207 * Here we don't create a new process, but we divorce
208 * certain parts of a process from itself.
210 if ((flags
& RFPROC
) == 0) {
212 vm_fork(p1
, 0, flags
);
215 * Close all file descriptors.
217 if (flags
& RFCFDG
) {
218 struct filedesc
*fdtmp
;
225 * Unshare file descriptors (from parent.)
228 if (p1
->p_fd
->fd_refcnt
> 1) {
229 struct filedesc
*newfd
;
240 * Although process entries are dynamically created, we still keep
241 * a global limit on the maximum number we will create. Don't allow
242 * a nonprivileged user to use the last ten processes; don't let root
243 * exceed the limit. The variable nprocs is the current number of
244 * processes, maxproc is the limit.
246 uid
= p1
->p_ucred
->cr_ruid
;
247 if ((nprocs
>= maxproc
- 10 && uid
!= 0) || nprocs
>= maxproc
) {
248 if (ppsratecheck(&lastfail
, &curfail
, 1))
249 printf("maxproc limit exceeded by uid %d, please "
250 "see tuning(7) and login.conf(5).\n", uid
);
251 tsleep(&forksleep
, 0, "fork", hz
/ 2);
255 * Increment the nprocs resource before blocking can occur. There
256 * are hard-limits as to the number of processes that can run.
261 * Increment the count of procs running with this uid. Don't allow
262 * a nonprivileged user to exceed their current limit.
264 ok
= chgproccnt(p1
->p_ucred
->cr_ruidinfo
, 1,
265 (uid
!= 0) ? p1
->p_rlimit
[RLIMIT_NPROC
].rlim_cur
: 0);
268 * Back out the process count
271 if (ppsratecheck(&lastfail
, &curfail
, 1))
272 printf("maxproc limit exceeded by uid %d, please "
273 "see tuning(7) and login.conf(5).\n", uid
);
274 tsleep(&forksleep
, 0, "fork", hz
/ 2);
278 /* Allocate new proc. */
279 newproc
= zalloc(proc_zone
);
282 * Setup linkage for kernel based threading XXX lwp
284 if ((flags
& RFTHREAD
) != 0) {
285 newproc
->p_peers
= p1
->p_peers
;
286 p1
->p_peers
= newproc
;
287 newproc
->p_leader
= p1
->p_leader
;
289 newproc
->p_peers
= 0;
290 newproc
->p_leader
= newproc
;
293 newproc
->p_wakeup
= 0;
294 newproc
->p_vmspace
= NULL
;
295 TAILQ_INIT(&newproc
->p_lwp
.lwp_sysmsgq
);
296 LIST_INIT(&newproc
->p_lwps
);
299 lp2
= &newproc
->p_lwp
;
300 lp2
->lwp_proc
= newproc
;
302 LIST_INSERT_HEAD(&newproc
->p_lwps
, lp2
, lwp_list
);
303 newproc
->p_nthreads
= 1;
306 * Find an unused process ID. We remember a range of unused IDs
307 * ready to use (from nextpid+1 through pidchecked-1).
311 nextpid
+= arc4random() % randompid
;
314 * If the process ID prototype has wrapped around,
315 * restart somewhat above 0, as the low-numbered procs
316 * tend to include daemons that don't exit.
318 if (nextpid
>= PID_MAX
) {
319 nextpid
= nextpid
% PID_MAX
;
324 if (nextpid
>= pidchecked
) {
327 pidchecked
= PID_MAX
;
329 * Scan the active and zombie procs to check whether this pid
330 * is in use. Remember the lowest pid that's greater
331 * than nextpid, so we can avoid checking for a while.
333 p2
= LIST_FIRST(&allproc
);
335 for (; p2
!= 0; p2
= LIST_NEXT(p2
, p_list
)) {
336 while (p2
->p_pid
== nextpid
||
337 p2
->p_pgrp
->pg_id
== nextpid
||
338 p2
->p_session
->s_sid
== nextpid
) {
340 if (nextpid
>= pidchecked
)
343 if (p2
->p_pid
> nextpid
&& pidchecked
> p2
->p_pid
)
344 pidchecked
= p2
->p_pid
;
345 if (p2
->p_pgrp
->pg_id
> nextpid
&&
346 pidchecked
> p2
->p_pgrp
->pg_id
)
347 pidchecked
= p2
->p_pgrp
->pg_id
;
348 if (p2
->p_session
->s_sid
> nextpid
&&
349 pidchecked
> p2
->p_session
->s_sid
)
350 pidchecked
= p2
->p_session
->s_sid
;
354 p2
= LIST_FIRST(&zombproc
);
360 p2
->p_stat
= SIDL
; /* protect against others */
362 LIST_INSERT_HEAD(&allproc
, p2
, p_list
);
363 LIST_INSERT_HEAD(PIDHASH(p2
->p_pid
), p2
, p_hash
);
366 * Make a proc table entry for the new process.
367 * Start by zeroing the section of proc that is zero-initialized,
368 * then copy the section that is copied directly from the parent.
370 bzero(&p2
->p_startzero
,
371 (unsigned) ((caddr_t
)&p2
->p_endzero
- (caddr_t
)&p2
->p_startzero
));
372 bzero(&lp2
->lwp_startzero
,
373 (unsigned) ((caddr_t
)&lp2
->lwp_endzero
-
374 (caddr_t
)&lp2
->lwp_startzero
));
375 bcopy(&p1
->p_startcopy
, &p2
->p_startcopy
,
376 (unsigned) ((caddr_t
)&p2
->p_endcopy
- (caddr_t
)&p2
->p_startcopy
));
377 bcopy(&p1
->p_lwp
.lwp_startcopy
, &lp2
->lwp_startcopy
,
378 (unsigned) ((caddr_t
)&lp2
->lwp_endcopy
-
379 (caddr_t
)&lp2
->lwp_startcopy
));
381 p2
->p_aioinfo
= NULL
;
384 * Duplicate sub-structures as needed.
385 * Increase reference counts on shared objects.
386 * The p_stats and p_sigacts substructs are set in vm_fork.
389 if (p1
->p_flag
& P_PROFIL
)
391 p2
->p_ucred
= crhold(p1
->p_ucred
);
393 if (jailed(p2
->p_ucred
))
394 p2
->p_flag
|= P_JAILED
;
397 p2
->p_args
->ar_ref
++;
399 if (flags
& RFSIGSHARE
) {
400 p2
->p_procsig
= p1
->p_procsig
;
401 p2
->p_procsig
->ps_refcnt
++;
402 if (p1
->p_sigacts
== &p1
->p_addr
->u_sigacts
) {
403 struct sigacts
*newsigacts
;
405 /* Create the shared sigacts structure */
406 MALLOC(newsigacts
, struct sigacts
*,
407 sizeof(struct sigacts
), M_SUBPROC
, M_WAITOK
);
410 * Set p_sigacts to the new shared structure.
411 * Note that this is updating p1->p_sigacts at the
412 * same time, since p_sigacts is just a pointer to
413 * the shared p_procsig->ps_sigacts.
415 p2
->p_sigacts
= newsigacts
;
416 bcopy(&p1
->p_addr
->u_sigacts
, p2
->p_sigacts
,
417 sizeof(*p2
->p_sigacts
));
418 *p2
->p_sigacts
= p1
->p_addr
->u_sigacts
;
422 MALLOC(p2
->p_procsig
, struct procsig
*, sizeof(struct procsig
),
423 M_SUBPROC
, M_WAITOK
);
424 bcopy(p1
->p_procsig
, p2
->p_procsig
, sizeof(*p2
->p_procsig
));
425 p2
->p_procsig
->ps_refcnt
= 1;
426 p2
->p_sigacts
= NULL
; /* finished in vm_fork() */
428 if (flags
& RFLINUXTHPN
)
429 p2
->p_sigparent
= SIGUSR1
;
431 p2
->p_sigparent
= SIGCHLD
;
433 /* bump references to the text vnode (for procfs) */
434 p2
->p_textvp
= p1
->p_textvp
;
438 if (flags
& RFCFDG
) {
439 p2
->p_fd
= fdinit(p1
);
441 } else if (flags
& RFFDG
) {
442 p2
->p_fd
= fdcopy(p1
);
445 p2
->p_fd
= fdshare(p1
);
446 if (p1
->p_fdtol
== NULL
)
448 filedesc_to_leader_alloc(NULL
,
450 if ((flags
& RFTHREAD
) != 0) {
452 * Shared file descriptor table and
453 * shared process leaders.
456 fdtol
->fdl_refcount
++;
459 * Shared file descriptor table, and
460 * different process leaders
462 fdtol
= filedesc_to_leader_alloc(p1
->p_fdtol
, p2
);
468 * If p_limit is still copy-on-write, bump refcnt,
469 * otherwise get a copy that won't be modified.
470 * (If PL_SHAREMOD is clear, the structure is shared
473 if (p1
->p_limit
->p_lflags
& PL_SHAREMOD
) {
474 p2
->p_limit
= limcopy(p1
->p_limit
);
476 p2
->p_limit
= p1
->p_limit
;
477 p2
->p_limit
->p_refcnt
++;
481 * Preserve some more flags in subprocess. P_PROFIL has already
484 p2
->p_flag
|= p1
->p_flag
& (P_SUGID
| P_ALTSTACK
);
485 if (p1
->p_session
->s_ttyvp
!= NULL
&& p1
->p_flag
& P_CONTROLT
)
486 p2
->p_flag
|= P_CONTROLT
;
487 if (flags
& RFPPWAIT
)
488 p2
->p_flag
|= P_PPWAIT
;
491 * Once we are on a pglist we may receive signals. XXX we might
492 * race a ^C being sent to the process group by not receiving it
493 * at all prior to this line.
495 LIST_INSERT_AFTER(p1
, p2
, p_pglist
);
498 * Attach the new process to its parent.
500 * If RFNOWAIT is set, the newly created process becomes a child
501 * of init. This effectively disassociates the child from the
504 if (flags
& RFNOWAIT
)
509 LIST_INSERT_HEAD(&pptr
->p_children
, p2
, p_sibling
);
510 LIST_INIT(&p2
->p_children
);
511 varsymset_init(&p2
->p_varsymset
, &p1
->p_varsymset
);
512 callout_init(&p2
->p_ithandle
);
516 * Copy traceflag and tracefile if enabled. If not inherited,
517 * these were zeroed above but we still could have a trace race
518 * so make sure p2's p_tracep is NULL.
520 if ((p1
->p_traceflag
& KTRFAC_INHERIT
) && p2
->p_tracep
== NULL
) {
521 p2
->p_traceflag
= p1
->p_traceflag
;
522 if ((p2
->p_tracep
= p1
->p_tracep
) != NULL
)
528 * Inherit the scheduler and initialize scheduler-related fields.
529 * Set cpbase to the last timeout that occured (not the upcoming
532 p2
->p_usched
= p1
->p_usched
;
533 lp2
->lwp_cpbase
= mycpu
->gd_schedclock
.time
-
534 mycpu
->gd_schedclock
.periodic
;
535 p2
->p_usched
->heuristic_forking(&p1
->p_lwp
, lp2
);
538 * This begins the section where we must prevent the parent
539 * from being swapped.
544 * Finish creating the child process. It will return via a different
545 * execution path later. (ie: directly into user mode)
547 vm_fork(p1
, p2
, flags
);
548 caps_fork(p1
, p2
, flags
);
550 if (flags
== (RFFDG
| RFPROC
)) {
551 mycpu
->gd_cnt
.v_forks
++;
552 mycpu
->gd_cnt
.v_forkpages
+= p2
->p_vmspace
->vm_dsize
+ p2
->p_vmspace
->vm_ssize
;
553 } else if (flags
== (RFFDG
| RFPROC
| RFPPWAIT
| RFMEM
)) {
554 mycpu
->gd_cnt
.v_vforks
++;
555 mycpu
->gd_cnt
.v_vforkpages
+= p2
->p_vmspace
->vm_dsize
+ p2
->p_vmspace
->vm_ssize
;
556 } else if (p1
== &proc0
) {
557 mycpu
->gd_cnt
.v_kthreads
++;
558 mycpu
->gd_cnt
.v_kthreadpages
+= p2
->p_vmspace
->vm_dsize
+ p2
->p_vmspace
->vm_ssize
;
560 mycpu
->gd_cnt
.v_rforks
++;
561 mycpu
->gd_cnt
.v_rforkpages
+= p2
->p_vmspace
->vm_dsize
+ p2
->p_vmspace
->vm_ssize
;
565 * Both processes are set up, now check if any loadable modules want
566 * to adjust anything.
567 * What if they have an error? XXX
569 TAILQ_FOREACH(ep
, &fork_list
, next
) {
570 (*ep
->function
)(p1
, p2
, flags
);
574 * Set the start time. Note that the process is not runnable. The
575 * caller is responsible for making it runnable.
577 microtime(&p2
->p_start
);
578 p2
->p_acflag
= AFORK
;
581 * tell any interested parties about the new process
583 KNOTE(&p1
->p_klist
, NOTE_FORK
| p2
->p_pid
);
586 * Return child proc pointer to parent.
593 * The next two functionms are general routines to handle adding/deleting
594 * items on the fork callout list.
597 * Take the arguments given and put them onto the fork callout list,
598 * However first make sure that it's not already there.
599 * Returns 0 on success or a standard error number.
602 at_fork(forklist_fn function
)
607 /* let the programmer know if he's been stupid */
608 if (rm_at_fork(function
)) {
609 printf("WARNING: fork callout entry (%p) already present\n",
613 ep
= malloc(sizeof(*ep
), M_ATFORK
, M_WAITOK
|M_ZERO
);
614 ep
->function
= function
;
615 TAILQ_INSERT_TAIL(&fork_list
, ep
, next
);
620 * Scan the exit callout list for the given item and remove it..
621 * Returns the number of items removed (0 or 1)
624 rm_at_fork(forklist_fn function
)
628 TAILQ_FOREACH(ep
, &fork_list
, next
) {
629 if (ep
->function
== function
) {
630 TAILQ_REMOVE(&fork_list
, ep
, next
);
639 * Add a forked process to the run queue after any remaining setup, such
640 * as setting the fork handler, has been completed.
643 start_forked_proc(struct lwp
*lp1
, struct proc
*p2
)
647 KKASSERT(p2
!= NULL
&& p2
->p_nthreads
== 1);
649 lp2
= LIST_FIRST(&p2
->p_lwps
);
652 * Move from SIDL to RUN queue, and activate the process's thread.
653 * Activation of the thread effectively makes the process "a"
654 * current process, so we do not setrunqueue().
656 * YYY setrunqueue works here but we should clean up the trampoline
657 * code so we just schedule the LWKT thread and let the trampoline
658 * deal with the userland scheduler on return to userland.
660 KASSERT(p2
->p_stat
== SIDL
,
661 ("cannot start forked process, bad status: %p", p2
));
662 p2
->p_usched
->resetpriority(lp2
);
665 p2
->p_usched
->setrunqueue(lp2
);
669 * Now can be swapped.
671 PRELE(lp1
->lwp_proc
);
674 * Preserve synchronization semantics of vfork. If waiting for
675 * child to exec or exit, set P_PPWAIT on child, and sleep on our
676 * proc (in case of exit).
678 while (p2
->p_flag
& P_PPWAIT
)
679 tsleep(lp1
->lwp_proc
, 0, "ppwait", 0);