xref: /freebsd/sys/kern/kern_acct.c (revision 195ebc7e9e4b129de810833791a19dfb4349d6a9)
1 /*-
2  * Copyright (c) 1982, 1986, 1989, 1993
3  *	The Regents of the University of California.  All rights reserved.
4  * (c) UNIX System Laboratories, Inc.
5  * Copyright (c) 2005 Robert N. M. Watson
6  * All rights reserved.
7  *
8  * All or some portions of this file are derived from material licensed
9  * to the University of California by American Telephone and Telegraph
10  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
11  * the permission of UNIX System Laboratories, Inc.
12  *
13  * Redistribution and use in source and binary forms, with or without
14  * modification, are permitted provided that the following conditions
15  * are met:
16  * 1. Redistributions of source code must retain the above copyright
17  *    notice, this list of conditions and the following disclaimer.
18  * 2. Redistributions in binary form must reproduce the above copyright
19  *    notice, this list of conditions and the following disclaimer in the
20  *    documentation and/or other materials provided with the distribution.
21  * 4. Neither the name of the University nor the names of its contributors
22  *    may be used to endorse or promote products derived from this software
23  *    without specific prior written permission.
24  *
25  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
26  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
27  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
28  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
29  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
30  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
31  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
32  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
33  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
34  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35  * SUCH DAMAGE.
36  *
37  * Copyright (c) 1994 Christopher G. Demetriou
38  *
39  * Redistribution and use in source and binary forms, with or without
40  * modification, are permitted provided that the following conditions
41  * are met:
42  * 1. Redistributions of source code must retain the above copyright
43  *    notice, this list of conditions and the following disclaimer.
44  * 2. Redistributions in binary form must reproduce the above copyright
45  *    notice, this list of conditions and the following disclaimer in the
46  *    documentation and/or other materials provided with the distribution.
47  * 3. All advertising materials mentioning features or use of this software
48  *    must display the following acknowledgement:
49  *	This product includes software developed by the University of
50  *	California, Berkeley and its contributors.
51  * 4. Neither the name of the University nor the names of its contributors
52  *    may be used to endorse or promote products derived from this software
53  *    without specific prior written permission.
54  *
55  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
56  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
57  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
58  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
59  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
60  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
61  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
62  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
63  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
64  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
65  * SUCH DAMAGE.
66  *
67  *	@(#)kern_acct.c	8.1 (Berkeley) 6/14/93
68  */
69 
70 #include <sys/cdefs.h>
71 __FBSDID("$FreeBSD$");
72 
73 #include "opt_mac.h"
74 
75 #include <sys/param.h>
76 #include <sys/systm.h>
77 #include <sys/acct.h>
78 #include <sys/fcntl.h>
79 #include <sys/kernel.h>
80 #include <sys/kthread.h>
81 #include <sys/limits.h>
82 #include <sys/lock.h>
83 #include <sys/mount.h>
84 #include <sys/mutex.h>
85 #include <sys/namei.h>
86 #include <sys/priv.h>
87 #include <sys/proc.h>
88 #include <sys/resourcevar.h>
89 #include <sys/sched.h>
90 #include <sys/sx.h>
91 #include <sys/sysctl.h>
92 #include <sys/sysent.h>
93 #include <sys/syslog.h>
94 #include <sys/sysproto.h>
95 #include <sys/tty.h>
96 #include <sys/vnode.h>
97 
98 #include <security/mac/mac_framework.h>
99 
100 /*
101  * The routines implemented in this file are described in:
102  *      Leffler, et al.: The Design and Implementation of the 4.3BSD
103  *	    UNIX Operating System (Addison Welley, 1989)
104  * on pages 62-63.
105  * On May 2007 the historic 3 bits base 8 exponent, 13 bit fraction
106  * compt_t representation described in the above reference was replaced
107  * with that of IEEE-754 floats.
108  *
109  * Arguably, to simplify accounting operations, this mechanism should
110  * be replaced by one in which an accounting log file (similar to /dev/klog)
111  * is read by a user process, etc.  However, that has its own problems.
112  */
113 
114 /* Floating point definitions from <float.h>. */
115 #define FLT_MANT_DIG    24              /* p */
116 #define FLT_MAX_EXP     128             /* emax */
117 
118 /*
119  * Internal accounting functions.
120  * The former's operation is described in Leffler, et al., and the latter
121  * was provided by UCB with the 4.4BSD-Lite release
122  */
123 static uint32_t	encode_timeval(struct timeval);
124 static uint32_t	encode_long(long);
125 static void	acctwatch(void);
126 static void	acct_thread(void *);
127 static int	acct_disable(struct thread *);
128 
129 /*
130  * Accounting vnode pointer, saved vnode pointer, and flags for each.
131  * acct_sx protects against changes to the active vnode and credentials
132  * while accounting records are being committed to disk.
133  */
134 static int		 acct_configured;
135 static int		 acct_suspended;
136 static struct vnode	*acct_vp;
137 static struct ucred	*acct_cred;
138 static int		 acct_flags;
139 static struct sx	 acct_sx;
140 
141 SX_SYSINIT(acct, &acct_sx, "acct_sx");
142 
143 /*
144  * State of the accounting kthread.
145  */
146 static int		 acct_state;
147 
148 #define	ACCT_RUNNING	1	/* Accounting kthread is running. */
149 #define	ACCT_EXITREQ	2	/* Accounting kthread should exit. */
150 
151 /*
152  * Values associated with enabling and disabling accounting
153  */
154 static int acctsuspend = 2;	/* stop accounting when < 2% free space left */
155 SYSCTL_INT(_kern, OID_AUTO, acct_suspend, CTLFLAG_RW,
156 	&acctsuspend, 0, "percentage of free disk space below which accounting stops");
157 
158 static int acctresume = 4;	/* resume when free space risen to > 4% */
159 SYSCTL_INT(_kern, OID_AUTO, acct_resume, CTLFLAG_RW,
160 	&acctresume, 0, "percentage of free disk space above which accounting resumes");
161 
162 static int acctchkfreq = 15;	/* frequency (in seconds) to check space */
163 
164 static int
165 sysctl_acct_chkfreq(SYSCTL_HANDLER_ARGS)
166 {
167 	int error, value;
168 
169 	/* Write out the old value. */
170 	error = SYSCTL_OUT(req, &acctchkfreq, sizeof(int));
171 	if (error || req->newptr == NULL)
172 		return (error);
173 
174 	/* Read in and verify the new value. */
175 	error = SYSCTL_IN(req, &value, sizeof(int));
176 	if (error)
177 		return (error);
178 	if (value <= 0)
179 		return (EINVAL);
180 	acctchkfreq = value;
181 	return (0);
182 }
183 SYSCTL_PROC(_kern, OID_AUTO, acct_chkfreq, CTLTYPE_INT|CTLFLAG_RW,
184     &acctchkfreq, 0, sysctl_acct_chkfreq, "I",
185     "frequency for checking the free space");
186 
187 SYSCTL_INT(_kern, OID_AUTO, acct_configured, CTLFLAG_RD, &acct_configured, 0,
188 	"Accounting configured or not");
189 
190 SYSCTL_INT(_kern, OID_AUTO, acct_suspended, CTLFLAG_RD, &acct_suspended, 0,
191 	"Accounting suspended or not");
192 
193 /*
194  * Accounting system call.  Written based on the specification and previous
195  * implementation done by Mark Tinguely.
196  */
197 int
198 acct(struct thread *td, struct acct_args *uap)
199 {
200 	struct nameidata nd;
201 	int error, flags, vfslocked;
202 
203 	error = priv_check(td, PRIV_ACCT);
204 	if (error)
205 		return (error);
206 
207 	/*
208 	 * If accounting is to be started to a file, open that file for
209 	 * appending and make sure it's a 'normal'.
210 	 */
211 	if (uap->path != NULL) {
212 		NDINIT(&nd, LOOKUP, NOFOLLOW | MPSAFE | AUDITVNODE1,
213 		    UIO_USERSPACE, uap->path, td);
214 		flags = FWRITE | O_APPEND;
215 		error = vn_open(&nd, &flags, 0, NULL);
216 		if (error)
217 			return (error);
218 		vfslocked = NDHASGIANT(&nd);
219 		NDFREE(&nd, NDF_ONLY_PNBUF);
220 #ifdef MAC
221 		error = mac_system_check_acct(td->td_ucred, nd.ni_vp);
222 		if (error) {
223 			VOP_UNLOCK(nd.ni_vp, 0);
224 			vn_close(nd.ni_vp, flags, td->td_ucred, td);
225 			VFS_UNLOCK_GIANT(vfslocked);
226 			return (error);
227 		}
228 #endif
229 		VOP_UNLOCK(nd.ni_vp, 0);
230 		if (nd.ni_vp->v_type != VREG) {
231 			vn_close(nd.ni_vp, flags, td->td_ucred, td);
232 			VFS_UNLOCK_GIANT(vfslocked);
233 			return (EACCES);
234 		}
235 		VFS_UNLOCK_GIANT(vfslocked);
236 #ifdef MAC
237 	} else {
238 		error = mac_system_check_acct(td->td_ucred, NULL);
239 		if (error)
240 			return (error);
241 #endif
242 	}
243 
244 	/*
245 	 * Disallow concurrent access to the accounting vnode while we swap
246 	 * it out, in order to prevent access after close.
247 	 */
248 	sx_xlock(&acct_sx);
249 
250 	/*
251 	 * If accounting was previously enabled, kill the old space-watcher,
252 	 * close the file, and (if no new file was specified, leave).  Reset
253 	 * the suspended state regardless of whether accounting remains
254 	 * enabled.
255 	 */
256 	acct_suspended = 0;
257 	if (acct_vp != NULL) {
258 		vfslocked = VFS_LOCK_GIANT(acct_vp->v_mount);
259 		error = acct_disable(td);
260 		VFS_UNLOCK_GIANT(vfslocked);
261 	}
262 	if (uap->path == NULL) {
263 		if (acct_state & ACCT_RUNNING) {
264 			acct_state |= ACCT_EXITREQ;
265 			wakeup(&acct_state);
266 		}
267 		sx_xunlock(&acct_sx);
268 		return (error);
269 	}
270 
271 	/*
272 	 * Save the new accounting file vnode, and schedule the new
273 	 * free space watcher.
274 	 */
275 	acct_vp = nd.ni_vp;
276 	acct_cred = crhold(td->td_ucred);
277 	acct_flags = flags;
278 	if (acct_state & ACCT_RUNNING)
279 		acct_state &= ~ACCT_EXITREQ;
280 	else {
281 		/*
282 		 * Try to start up an accounting kthread.  We may start more
283 		 * than one, but if so the extras will commit suicide as
284 		 * soon as they start up.
285 		 */
286 		error = kproc_create(acct_thread, NULL, NULL, 0, 0,
287 		    "accounting");
288 		if (error) {
289 			vfslocked = VFS_LOCK_GIANT(acct_vp->v_mount);
290 			(void) vn_close(acct_vp, acct_flags, acct_cred, td);
291 			VFS_UNLOCK_GIANT(vfslocked);
292 			crfree(acct_cred);
293 			acct_configured = 0;
294 			acct_vp = NULL;
295 			acct_cred = NULL;
296 			acct_flags = 0;
297 			sx_xunlock(&acct_sx);
298 			log(LOG_NOTICE, "Unable to start accounting thread\n");
299 			return (error);
300 		}
301 	}
302 	acct_configured = 1;
303 	sx_xunlock(&acct_sx);
304 	log(LOG_NOTICE, "Accounting enabled\n");
305 	return (error);
306 }
307 
308 /*
309  * Disable currently in-progress accounting by closing the vnode, dropping
310  * our reference to the credential, and clearing the vnode's flags.
311  */
312 static int
313 acct_disable(struct thread *td)
314 {
315 	int error;
316 
317 	sx_assert(&acct_sx, SX_XLOCKED);
318 	error = vn_close(acct_vp, acct_flags, acct_cred, td);
319 	crfree(acct_cred);
320 	acct_configured = 0;
321 	acct_vp = NULL;
322 	acct_cred = NULL;
323 	acct_flags = 0;
324 	log(LOG_NOTICE, "Accounting disabled\n");
325 	return (error);
326 }
327 
328 /*
329  * Write out process accounting information, on process exit.
330  * Data to be written out is specified in Leffler, et al.
331  * and are enumerated below.  (They're also noted in the system
332  * "acct.h" header file.)
333  */
334 int
335 acct_process(struct thread *td)
336 {
337 	struct acctv2 acct;
338 	struct timeval ut, st, tmp;
339 	struct plimit *newlim, *oldlim;
340 	struct proc *p;
341 	struct rusage ru;
342 	int t, ret, vfslocked;
343 
344 	/*
345 	 * Lockless check of accounting condition before doing the hard
346 	 * work.
347 	 */
348 	if (acct_vp == NULL || acct_suspended)
349 		return (0);
350 
351 	sx_slock(&acct_sx);
352 
353 	/*
354 	 * If accounting isn't enabled, don't bother.  Have to check again
355 	 * once we own the lock in case we raced with disabling of accounting
356 	 * by another thread.
357 	 */
358 	if (acct_vp == NULL || acct_suspended) {
359 		sx_sunlock(&acct_sx);
360 		return (0);
361 	}
362 
363 	p = td->td_proc;
364 
365 	/*
366 	 * Get process accounting information.
367 	 */
368 
369 	sx_slock(&proctree_lock);
370 	PROC_LOCK(p);
371 
372 	/* (1) The terminal from which the process was started */
373 	if ((p->p_flag & P_CONTROLT) && p->p_pgrp->pg_session->s_ttyp)
374 		acct.ac_tty = tty_udev(p->p_pgrp->pg_session->s_ttyp);
375 	else
376 		acct.ac_tty = NODEV;
377 	sx_sunlock(&proctree_lock);
378 
379 	/* (2) The name of the command that ran */
380 	bcopy(p->p_comm, acct.ac_comm, sizeof acct.ac_comm);
381 
382 	/* (3) The amount of user and system time that was used */
383 	rufetchcalc(p, &ru, &ut, &st);
384 	acct.ac_utime = encode_timeval(ut);
385 	acct.ac_stime = encode_timeval(st);
386 
387 	/* (4) The elapsed time the command ran (and its starting time) */
388 	tmp = boottime;
389 	timevaladd(&tmp, &p->p_stats->p_start);
390 	acct.ac_btime = tmp.tv_sec;
391 	microuptime(&tmp);
392 	timevalsub(&tmp, &p->p_stats->p_start);
393 	acct.ac_etime = encode_timeval(tmp);
394 
395 	/* (5) The average amount of memory used */
396 	tmp = ut;
397 	timevaladd(&tmp, &st);
398 	/* Convert tmp (i.e. u + s) into hz units to match ru_i*. */
399 	t = tmp.tv_sec * hz + tmp.tv_usec / tick;
400 	if (t)
401 		acct.ac_mem = encode_long((ru.ru_ixrss + ru.ru_idrss +
402 		    + ru.ru_isrss) / t);
403 	else
404 		acct.ac_mem = 0;
405 
406 	/* (6) The number of disk I/O operations done */
407 	acct.ac_io = encode_long(ru.ru_inblock + ru.ru_oublock);
408 
409 	/* (7) The UID and GID of the process */
410 	acct.ac_uid = p->p_ucred->cr_ruid;
411 	acct.ac_gid = p->p_ucred->cr_rgid;
412 
413 	/* (8) The boolean flags that tell how the process terminated, etc. */
414 	acct.ac_flagx = p->p_acflag;
415 	PROC_UNLOCK(p);
416 
417 	/* Setup ancillary structure fields. */
418 	acct.ac_flagx |= ANVER;
419 	acct.ac_zero = 0;
420 	acct.ac_version = 2;
421 	acct.ac_len = acct.ac_len2 = sizeof(acct);
422 
423 	/*
424 	 * Eliminate any file size rlimit.
425 	 */
426 	newlim = lim_alloc();
427 	PROC_LOCK(p);
428 	oldlim = p->p_limit;
429 	lim_copy(newlim, oldlim);
430 	newlim->pl_rlimit[RLIMIT_FSIZE].rlim_cur = RLIM_INFINITY;
431 	p->p_limit = newlim;
432 	PROC_UNLOCK(p);
433 	lim_free(oldlim);
434 
435 	/*
436 	 * Write the accounting information to the file.
437 	 */
438 	vfslocked = VFS_LOCK_GIANT(acct_vp->v_mount);
439 	ret = vn_rdwr(UIO_WRITE, acct_vp, (caddr_t)&acct, sizeof (acct),
440 	    (off_t)0, UIO_SYSSPACE, IO_APPEND|IO_UNIT, acct_cred, NOCRED,
441 	    (int *)0, td);
442 	VFS_UNLOCK_GIANT(vfslocked);
443 	sx_sunlock(&acct_sx);
444 	return (ret);
445 }
446 
447 /* FLOAT_CONVERSION_START (Regression testing; don't remove this line.) */
448 
449 /* Convert timevals and longs into IEEE-754 bit patterns. */
450 
451 /* Mantissa mask (MSB is implied, so subtract 1). */
452 #define MANT_MASK ((1 << (FLT_MANT_DIG - 1)) - 1)
453 
454 /*
455  * We calculate integer values to a precision of approximately
456  * 28 bits.
457  * This is high-enough precision to fill the 24 float bits
458  * and low-enough to avoid overflowing the 32 int bits.
459  */
460 #define CALC_BITS 28
461 
462 /* log_2(1000000). */
463 #define LOG2_1M 20
464 
465 /*
466  * Convert the elements of a timeval into a 32-bit word holding
467  * the bits of a IEEE-754 float.
468  * The float value represents the timeval's value in microsecond units.
469  */
470 static uint32_t
471 encode_timeval(struct timeval tv)
472 {
473 	int log2_s;
474 	int val, exp;	/* Unnormalized value and exponent */
475 	int norm_exp;	/* Normalized exponent */
476 	int shift;
477 
478 	/*
479 	 * First calculate value and exponent to about CALC_BITS precision.
480 	 * Note that the following conditionals have been ordered so that
481 	 * the most common cases appear first.
482 	 */
483 	if (tv.tv_sec == 0) {
484 		if (tv.tv_usec == 0)
485 			return (0);
486 		exp = 0;
487 		val = tv.tv_usec;
488 	} else {
489 		/*
490 		 * Calculate the value to a precision of approximately
491 		 * CALC_BITS.
492 		 */
493 		log2_s = fls(tv.tv_sec) - 1;
494 		if (log2_s + LOG2_1M < CALC_BITS) {
495 			exp = 0;
496 			val = 1000000 * tv.tv_sec + tv.tv_usec;
497 		} else {
498 			exp = log2_s + LOG2_1M - CALC_BITS;
499 			val = (unsigned int)(((u_int64_t)1000000 * tv.tv_sec +
500 			    tv.tv_usec) >> exp);
501 		}
502 	}
503 	/* Now normalize and pack the value into an IEEE-754 float. */
504 	norm_exp = fls(val) - 1;
505 	shift = FLT_MANT_DIG - norm_exp - 1;
506 #ifdef ACCT_DEBUG
507 	printf("val=%d exp=%d shift=%d log2(val)=%d\n",
508 	    val, exp, shift, norm_exp);
509 	printf("exp=%x mant=%x\n", FLT_MAX_EXP - 1 + exp + norm_exp,
510 	    ((shift > 0 ? (val << shift) : (val >> -shift)) & MANT_MASK));
511 #endif
512 	return (((FLT_MAX_EXP - 1 + exp + norm_exp) << (FLT_MANT_DIG - 1)) |
513 	    ((shift > 0 ? val << shift : val >> -shift) & MANT_MASK));
514 }
515 
516 /*
517  * Convert a non-negative long value into the bit pattern of
518  * an IEEE-754 float value.
519  */
520 static uint32_t
521 encode_long(long val)
522 {
523 	int norm_exp;	/* Normalized exponent */
524 	int shift;
525 
526 	if (val == 0)
527 		return (0);
528 	if (val < 0) {
529 		log(LOG_NOTICE,
530 		    "encode_long: negative value %ld in accounting record\n",
531 		    val);
532 		val = LONG_MAX;
533 	}
534 	norm_exp = fls(val) - 1;
535 	shift = FLT_MANT_DIG - norm_exp - 1;
536 #ifdef ACCT_DEBUG
537 	printf("val=%d shift=%d log2(val)=%d\n",
538 	    val, shift, norm_exp);
539 	printf("exp=%x mant=%x\n", FLT_MAX_EXP - 1 + exp + norm_exp,
540 	    ((shift > 0 ? (val << shift) : (val >> -shift)) & MANT_MASK));
541 #endif
542 	return (((FLT_MAX_EXP - 1 + norm_exp) << (FLT_MANT_DIG - 1)) |
543 	    ((shift > 0 ? val << shift : val >> -shift) & MANT_MASK));
544 }
545 
546 /* FLOAT_CONVERSION_END (Regression testing; don't remove this line.) */
547 
548 /*
549  * Periodically check the filesystem to see if accounting
550  * should be turned on or off.  Beware the case where the vnode
551  * has been vgone()'d out from underneath us, e.g. when the file
552  * system containing the accounting file has been forcibly unmounted.
553  */
554 /* ARGSUSED */
555 static void
556 acctwatch(void)
557 {
558 	struct statfs sb;
559 	int vfslocked;
560 
561 	sx_assert(&acct_sx, SX_XLOCKED);
562 
563 	/*
564 	 * If accounting was disabled before our kthread was scheduled,
565 	 * then acct_vp might be NULL.  If so, just ask our kthread to
566 	 * exit and return.
567 	 */
568 	if (acct_vp == NULL) {
569 		acct_state |= ACCT_EXITREQ;
570 		return;
571 	}
572 
573 	/*
574 	 * If our vnode is no longer valid, tear it down and signal the
575 	 * accounting thread to die.
576 	 */
577 	vfslocked = VFS_LOCK_GIANT(acct_vp->v_mount);
578 	if (acct_vp->v_type == VBAD) {
579 		(void) acct_disable(NULL);
580 		VFS_UNLOCK_GIANT(vfslocked);
581 		acct_state |= ACCT_EXITREQ;
582 		return;
583 	}
584 
585 	/*
586 	 * Stopping here is better than continuing, maybe it will be VBAD
587 	 * next time around.
588 	 */
589 	if (VFS_STATFS(acct_vp->v_mount, &sb) < 0) {
590 		VFS_UNLOCK_GIANT(vfslocked);
591 		return;
592 	}
593 	VFS_UNLOCK_GIANT(vfslocked);
594 	if (acct_suspended) {
595 		if (sb.f_bavail > (int64_t)(acctresume * sb.f_blocks /
596 		    100)) {
597 			acct_suspended = 0;
598 			log(LOG_NOTICE, "Accounting resumed\n");
599 		}
600 	} else {
601 		if (sb.f_bavail <= (int64_t)(acctsuspend * sb.f_blocks /
602 		    100)) {
603 			acct_suspended = 1;
604 			log(LOG_NOTICE, "Accounting suspended\n");
605 		}
606 	}
607 }
608 
609 /*
610  * The main loop for the dedicated kernel thread that periodically calls
611  * acctwatch().
612  */
613 static void
614 acct_thread(void *dummy)
615 {
616 	u_char pri;
617 
618 	/* This is a low-priority kernel thread. */
619 	pri = PRI_MAX_KERN;
620 	thread_lock(curthread);
621 	sched_prio(curthread, pri);
622 	thread_unlock(curthread);
623 
624 	/* If another accounting kthread is already running, just die. */
625 	sx_xlock(&acct_sx);
626 	if (acct_state & ACCT_RUNNING) {
627 		sx_xunlock(&acct_sx);
628 		kproc_exit(0);
629 	}
630 	acct_state |= ACCT_RUNNING;
631 
632 	/* Loop until we are asked to exit. */
633 	while (!(acct_state & ACCT_EXITREQ)) {
634 
635 		/* Perform our periodic checks. */
636 		acctwatch();
637 
638 		/*
639 		 * We check this flag again before sleeping since the
640 		 * acctwatch() might have shut down accounting and asked us
641 		 * to exit.
642 		 */
643 		if (!(acct_state & ACCT_EXITREQ)) {
644 			sx_sleep(&acct_state, &acct_sx, 0, "-",
645 			    acctchkfreq * hz);
646 		}
647 	}
648 
649 	/*
650 	 * Acknowledge the exit request and shutdown.  We clear both the
651 	 * exit request and running flags.
652 	 */
653 	acct_state = 0;
654 	sx_xunlock(&acct_sx);
655 	kproc_exit(0);
656 }
657