The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_acct.c

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    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: releng/9.0/sys/kern/kern_acct.c 225617 2011-09-16 13:58:51Z kmacy $");
   72 
   73 #include <sys/param.h>
   74 #include <sys/systm.h>
   75 #include <sys/acct.h>
   76 #include <sys/fcntl.h>
   77 #include <sys/kernel.h>
   78 #include <sys/kthread.h>
   79 #include <sys/limits.h>
   80 #include <sys/lock.h>
   81 #include <sys/mount.h>
   82 #include <sys/mutex.h>
   83 #include <sys/namei.h>
   84 #include <sys/priv.h>
   85 #include <sys/proc.h>
   86 #include <sys/resourcevar.h>
   87 #include <sys/sched.h>
   88 #include <sys/sx.h>
   89 #include <sys/sysctl.h>
   90 #include <sys/sysent.h>
   91 #include <sys/syslog.h>
   92 #include <sys/sysproto.h>
   93 #include <sys/tty.h>
   94 #include <sys/vnode.h>
   95 
   96 #include <security/mac/mac_framework.h>
   97 
   98 /*
   99  * The routines implemented in this file are described in:
  100  *      Leffler, et al.: The Design and Implementation of the 4.3BSD
  101  *          UNIX Operating System (Addison Welley, 1989)
  102  * on pages 62-63.
  103  * On May 2007 the historic 3 bits base 8 exponent, 13 bit fraction
  104  * compt_t representation described in the above reference was replaced
  105  * with that of IEEE-754 floats.
  106  *
  107  * Arguably, to simplify accounting operations, this mechanism should
  108  * be replaced by one in which an accounting log file (similar to /dev/klog)
  109  * is read by a user process, etc.  However, that has its own problems.
  110  */
  111 
  112 /* Floating point definitions from <float.h>. */
  113 #define FLT_MANT_DIG    24              /* p */
  114 #define FLT_MAX_EXP     128             /* emax */
  115 
  116 /*
  117  * Internal accounting functions.
  118  * The former's operation is described in Leffler, et al., and the latter
  119  * was provided by UCB with the 4.4BSD-Lite release
  120  */
  121 static uint32_t encode_timeval(struct timeval);
  122 static uint32_t encode_long(long);
  123 static void     acctwatch(void);
  124 static void     acct_thread(void *);
  125 static int      acct_disable(struct thread *);
  126 
  127 /*
  128  * Accounting vnode pointer, saved vnode pointer, and flags for each.
  129  * acct_sx protects against changes to the active vnode and credentials
  130  * while accounting records are being committed to disk.
  131  */
  132 static int               acct_configured;
  133 static int               acct_suspended;
  134 static struct vnode     *acct_vp;
  135 static struct ucred     *acct_cred;
  136 static int               acct_flags;
  137 static struct sx         acct_sx;
  138 
  139 SX_SYSINIT(acct, &acct_sx, "acct_sx");
  140 
  141 /*
  142  * State of the accounting kthread.
  143  */
  144 static int               acct_state;
  145 
  146 #define ACCT_RUNNING    1       /* Accounting kthread is running. */
  147 #define ACCT_EXITREQ    2       /* Accounting kthread should exit. */
  148 
  149 /*
  150  * Values associated with enabling and disabling accounting
  151  */
  152 static int acctsuspend = 2;     /* stop accounting when < 2% free space left */
  153 SYSCTL_INT(_kern, OID_AUTO, acct_suspend, CTLFLAG_RW,
  154         &acctsuspend, 0, "percentage of free disk space below which accounting stops");
  155 
  156 static int acctresume = 4;      /* resume when free space risen to > 4% */
  157 SYSCTL_INT(_kern, OID_AUTO, acct_resume, CTLFLAG_RW,
  158         &acctresume, 0, "percentage of free disk space above which accounting resumes");
  159 
  160 static int acctchkfreq = 15;    /* frequency (in seconds) to check space */
  161 
  162 static int
  163 sysctl_acct_chkfreq(SYSCTL_HANDLER_ARGS)
  164 {
  165         int error, value;
  166 
  167         /* Write out the old value. */
  168         error = SYSCTL_OUT(req, &acctchkfreq, sizeof(int));
  169         if (error || req->newptr == NULL)
  170                 return (error);
  171 
  172         /* Read in and verify the new value. */
  173         error = SYSCTL_IN(req, &value, sizeof(int));
  174         if (error)
  175                 return (error);
  176         if (value <= 0)
  177                 return (EINVAL);
  178         acctchkfreq = value;
  179         return (0);
  180 }
  181 SYSCTL_PROC(_kern, OID_AUTO, acct_chkfreq, CTLTYPE_INT|CTLFLAG_RW,
  182     &acctchkfreq, 0, sysctl_acct_chkfreq, "I",
  183     "frequency for checking the free space");
  184 
  185 SYSCTL_INT(_kern, OID_AUTO, acct_configured, CTLFLAG_RD, &acct_configured, 0,
  186         "Accounting configured or not");
  187 
  188 SYSCTL_INT(_kern, OID_AUTO, acct_suspended, CTLFLAG_RD, &acct_suspended, 0,
  189         "Accounting suspended or not");
  190 
  191 /*
  192  * Accounting system call.  Written based on the specification and previous
  193  * implementation done by Mark Tinguely.
  194  */
  195 int
  196 sys_acct(struct thread *td, struct acct_args *uap)
  197 {
  198         struct nameidata nd;
  199         int error, flags, vfslocked;
  200 
  201         error = priv_check(td, PRIV_ACCT);
  202         if (error)
  203                 return (error);
  204 
  205         /*
  206          * If accounting is to be started to a file, open that file for
  207          * appending and make sure it's a 'normal'.
  208          */
  209         if (uap->path != NULL) {
  210                 NDINIT(&nd, LOOKUP, NOFOLLOW | MPSAFE | AUDITVNODE1,
  211                     UIO_USERSPACE, uap->path, td);
  212                 flags = FWRITE | O_APPEND;
  213                 error = vn_open(&nd, &flags, 0, NULL);
  214                 if (error)
  215                         return (error);
  216                 vfslocked = NDHASGIANT(&nd);
  217                 NDFREE(&nd, NDF_ONLY_PNBUF);
  218 #ifdef MAC
  219                 error = mac_system_check_acct(td->td_ucred, nd.ni_vp);
  220                 if (error) {
  221                         VOP_UNLOCK(nd.ni_vp, 0);
  222                         vn_close(nd.ni_vp, flags, td->td_ucred, td);
  223                         VFS_UNLOCK_GIANT(vfslocked);
  224                         return (error);
  225                 }
  226 #endif
  227                 VOP_UNLOCK(nd.ni_vp, 0);
  228                 if (nd.ni_vp->v_type != VREG) {
  229                         vn_close(nd.ni_vp, flags, td->td_ucred, td);
  230                         VFS_UNLOCK_GIANT(vfslocked);
  231                         return (EACCES);
  232                 }
  233                 VFS_UNLOCK_GIANT(vfslocked);
  234 #ifdef MAC
  235         } else {
  236                 error = mac_system_check_acct(td->td_ucred, NULL);
  237                 if (error)
  238                         return (error);
  239 #endif
  240         }
  241 
  242         /*
  243          * Disallow concurrent access to the accounting vnode while we swap
  244          * it out, in order to prevent access after close.
  245          */
  246         sx_xlock(&acct_sx);
  247 
  248         /*
  249          * If accounting was previously enabled, kill the old space-watcher,
  250          * close the file, and (if no new file was specified, leave).  Reset
  251          * the suspended state regardless of whether accounting remains
  252          * enabled.
  253          */
  254         acct_suspended = 0;
  255         if (acct_vp != NULL) {
  256                 vfslocked = VFS_LOCK_GIANT(acct_vp->v_mount);
  257                 error = acct_disable(td);
  258                 VFS_UNLOCK_GIANT(vfslocked);
  259         }
  260         if (uap->path == NULL) {
  261                 if (acct_state & ACCT_RUNNING) {
  262                         acct_state |= ACCT_EXITREQ;
  263                         wakeup(&acct_state);
  264                 }
  265                 sx_xunlock(&acct_sx);
  266                 return (error);
  267         }
  268 
  269         /*
  270          * Save the new accounting file vnode, and schedule the new
  271          * free space watcher.
  272          */
  273         acct_vp = nd.ni_vp;
  274         acct_cred = crhold(td->td_ucred);
  275         acct_flags = flags;
  276         if (acct_state & ACCT_RUNNING)
  277                 acct_state &= ~ACCT_EXITREQ;
  278         else {
  279                 /*
  280                  * Try to start up an accounting kthread.  We may start more
  281                  * than one, but if so the extras will commit suicide as
  282                  * soon as they start up.
  283                  */
  284                 error = kproc_create(acct_thread, NULL, NULL, 0, 0,
  285                     "accounting");
  286                 if (error) {
  287                         vfslocked = VFS_LOCK_GIANT(acct_vp->v_mount);
  288                         (void) vn_close(acct_vp, acct_flags, acct_cred, td);
  289                         VFS_UNLOCK_GIANT(vfslocked);
  290                         crfree(acct_cred);
  291                         acct_configured = 0;
  292                         acct_vp = NULL;
  293                         acct_cred = NULL;
  294                         acct_flags = 0;
  295                         sx_xunlock(&acct_sx);
  296                         log(LOG_NOTICE, "Unable to start accounting thread\n");
  297                         return (error);
  298                 }
  299         }
  300         acct_configured = 1;
  301         sx_xunlock(&acct_sx);
  302         log(LOG_NOTICE, "Accounting enabled\n");
  303         return (error);
  304 }
  305 
  306 /*
  307  * Disable currently in-progress accounting by closing the vnode, dropping
  308  * our reference to the credential, and clearing the vnode's flags.
  309  */
  310 static int
  311 acct_disable(struct thread *td)
  312 {
  313         int error;
  314 
  315         sx_assert(&acct_sx, SX_XLOCKED);
  316         error = vn_close(acct_vp, acct_flags, acct_cred, td);
  317         crfree(acct_cred);
  318         acct_configured = 0;
  319         acct_vp = NULL;
  320         acct_cred = NULL;
  321         acct_flags = 0;
  322         log(LOG_NOTICE, "Accounting disabled\n");
  323         return (error);
  324 }
  325 
  326 /*
  327  * Write out process accounting information, on process exit.
  328  * Data to be written out is specified in Leffler, et al.
  329  * and are enumerated below.  (They're also noted in the system
  330  * "acct.h" header file.)
  331  */
  332 int
  333 acct_process(struct thread *td)
  334 {
  335         struct acctv2 acct;
  336         struct timeval ut, st, tmp;
  337         struct plimit *newlim, *oldlim;
  338         struct proc *p;
  339         struct rusage ru;
  340         int t, ret, vfslocked;
  341 
  342         /*
  343          * Lockless check of accounting condition before doing the hard
  344          * work.
  345          */
  346         if (acct_vp == NULL || acct_suspended)
  347                 return (0);
  348 
  349         sx_slock(&acct_sx);
  350 
  351         /*
  352          * If accounting isn't enabled, don't bother.  Have to check again
  353          * once we own the lock in case we raced with disabling of accounting
  354          * by another thread.
  355          */
  356         if (acct_vp == NULL || acct_suspended) {
  357                 sx_sunlock(&acct_sx);
  358                 return (0);
  359         }
  360 
  361         p = td->td_proc;
  362 
  363         /*
  364          * Get process accounting information.
  365          */
  366 
  367         sx_slock(&proctree_lock);
  368         PROC_LOCK(p);
  369 
  370         /* (1) The terminal from which the process was started */
  371         if ((p->p_flag & P_CONTROLT) && p->p_pgrp->pg_session->s_ttyp)
  372                 acct.ac_tty = tty_udev(p->p_pgrp->pg_session->s_ttyp);
  373         else
  374                 acct.ac_tty = NODEV;
  375         sx_sunlock(&proctree_lock);
  376 
  377         /* (2) The name of the command that ran */
  378         bcopy(p->p_comm, acct.ac_comm, sizeof acct.ac_comm);
  379 
  380         /* (3) The amount of user and system time that was used */
  381         rufetchcalc(p, &ru, &ut, &st);
  382         acct.ac_utime = encode_timeval(ut);
  383         acct.ac_stime = encode_timeval(st);
  384 
  385         /* (4) The elapsed time the command ran (and its starting time) */
  386         tmp = boottime;
  387         timevaladd(&tmp, &p->p_stats->p_start);
  388         acct.ac_btime = tmp.tv_sec;
  389         microuptime(&tmp);
  390         timevalsub(&tmp, &p->p_stats->p_start);
  391         acct.ac_etime = encode_timeval(tmp);
  392 
  393         /* (5) The average amount of memory used */
  394         tmp = ut;
  395         timevaladd(&tmp, &st);
  396         /* Convert tmp (i.e. u + s) into hz units to match ru_i*. */
  397         t = tmp.tv_sec * hz + tmp.tv_usec / tick;
  398         if (t)
  399                 acct.ac_mem = encode_long((ru.ru_ixrss + ru.ru_idrss +
  400                     + ru.ru_isrss) / t);
  401         else
  402                 acct.ac_mem = 0;
  403 
  404         /* (6) The number of disk I/O operations done */
  405         acct.ac_io = encode_long(ru.ru_inblock + ru.ru_oublock);
  406 
  407         /* (7) The UID and GID of the process */
  408         acct.ac_uid = p->p_ucred->cr_ruid;
  409         acct.ac_gid = p->p_ucred->cr_rgid;
  410 
  411         /* (8) The boolean flags that tell how the process terminated, etc. */
  412         acct.ac_flagx = p->p_acflag;
  413         PROC_UNLOCK(p);
  414 
  415         /* Setup ancillary structure fields. */
  416         acct.ac_flagx |= ANVER;
  417         acct.ac_zero = 0;
  418         acct.ac_version = 2;
  419         acct.ac_len = acct.ac_len2 = sizeof(acct);
  420 
  421         /*
  422          * Eliminate any file size rlimit.
  423          */
  424         newlim = lim_alloc();
  425         PROC_LOCK(p);
  426         oldlim = p->p_limit;
  427         lim_copy(newlim, oldlim);
  428         newlim->pl_rlimit[RLIMIT_FSIZE].rlim_cur = RLIM_INFINITY;
  429         p->p_limit = newlim;
  430         PROC_UNLOCK(p);
  431         lim_free(oldlim);
  432 
  433         /*
  434          * Write the accounting information to the file.
  435          */
  436         vfslocked = VFS_LOCK_GIANT(acct_vp->v_mount);
  437         ret = vn_rdwr(UIO_WRITE, acct_vp, (caddr_t)&acct, sizeof (acct),
  438             (off_t)0, UIO_SYSSPACE, IO_APPEND|IO_UNIT, acct_cred, NOCRED,
  439             NULL, td);
  440         VFS_UNLOCK_GIANT(vfslocked);
  441         sx_sunlock(&acct_sx);
  442         return (ret);
  443 }
  444 
  445 /* FLOAT_CONVERSION_START (Regression testing; don't remove this line.) */
  446 
  447 /* Convert timevals and longs into IEEE-754 bit patterns. */
  448 
  449 /* Mantissa mask (MSB is implied, so subtract 1). */
  450 #define MANT_MASK ((1 << (FLT_MANT_DIG - 1)) - 1)
  451 
  452 /*
  453  * We calculate integer values to a precision of approximately
  454  * 28 bits.
  455  * This is high-enough precision to fill the 24 float bits
  456  * and low-enough to avoid overflowing the 32 int bits.
  457  */
  458 #define CALC_BITS 28
  459 
  460 /* log_2(1000000). */
  461 #define LOG2_1M 20
  462 
  463 /*
  464  * Convert the elements of a timeval into a 32-bit word holding
  465  * the bits of a IEEE-754 float.
  466  * The float value represents the timeval's value in microsecond units.
  467  */
  468 static uint32_t
  469 encode_timeval(struct timeval tv)
  470 {
  471         int log2_s;
  472         int val, exp;   /* Unnormalized value and exponent */
  473         int norm_exp;   /* Normalized exponent */
  474         int shift;
  475 
  476         /*
  477          * First calculate value and exponent to about CALC_BITS precision.
  478          * Note that the following conditionals have been ordered so that
  479          * the most common cases appear first.
  480          */
  481         if (tv.tv_sec == 0) {
  482                 if (tv.tv_usec == 0)
  483                         return (0);
  484                 exp = 0;
  485                 val = tv.tv_usec;
  486         } else {
  487                 /*
  488                  * Calculate the value to a precision of approximately
  489                  * CALC_BITS.
  490                  */
  491                 log2_s = fls(tv.tv_sec) - 1;
  492                 if (log2_s + LOG2_1M < CALC_BITS) {
  493                         exp = 0;
  494                         val = 1000000 * tv.tv_sec + tv.tv_usec;
  495                 } else {
  496                         exp = log2_s + LOG2_1M - CALC_BITS;
  497                         val = (unsigned int)(((uint64_t)1000000 * tv.tv_sec +
  498                             tv.tv_usec) >> exp);
  499                 }
  500         }
  501         /* Now normalize and pack the value into an IEEE-754 float. */
  502         norm_exp = fls(val) - 1;
  503         shift = FLT_MANT_DIG - norm_exp - 1;
  504 #ifdef ACCT_DEBUG
  505         printf("val=%d exp=%d shift=%d log2(val)=%d\n",
  506             val, exp, shift, norm_exp);
  507         printf("exp=%x mant=%x\n", FLT_MAX_EXP - 1 + exp + norm_exp,
  508             ((shift > 0 ? (val << shift) : (val >> -shift)) & MANT_MASK));
  509 #endif
  510         return (((FLT_MAX_EXP - 1 + exp + norm_exp) << (FLT_MANT_DIG - 1)) |
  511             ((shift > 0 ? val << shift : val >> -shift) & MANT_MASK));
  512 }
  513 
  514 /*
  515  * Convert a non-negative long value into the bit pattern of
  516  * an IEEE-754 float value.
  517  */
  518 static uint32_t
  519 encode_long(long val)
  520 {
  521         int norm_exp;   /* Normalized exponent */
  522         int shift;
  523 
  524         if (val == 0)
  525                 return (0);
  526         if (val < 0) {
  527                 log(LOG_NOTICE,
  528                     "encode_long: negative value %ld in accounting record\n",
  529                     val);
  530                 val = LONG_MAX;
  531         }
  532         norm_exp = fls(val) - 1;
  533         shift = FLT_MANT_DIG - norm_exp - 1;
  534 #ifdef ACCT_DEBUG
  535         printf("val=%d shift=%d log2(val)=%d\n",
  536             val, shift, norm_exp);
  537         printf("exp=%x mant=%x\n", FLT_MAX_EXP - 1 + exp + norm_exp,
  538             ((shift > 0 ? (val << shift) : (val >> -shift)) & MANT_MASK));
  539 #endif
  540         return (((FLT_MAX_EXP - 1 + norm_exp) << (FLT_MANT_DIG - 1)) |
  541             ((shift > 0 ? val << shift : val >> -shift) & MANT_MASK));
  542 }
  543 
  544 /* FLOAT_CONVERSION_END (Regression testing; don't remove this line.) */
  545 
  546 /*
  547  * Periodically check the filesystem to see if accounting
  548  * should be turned on or off.  Beware the case where the vnode
  549  * has been vgone()'d out from underneath us, e.g. when the file
  550  * system containing the accounting file has been forcibly unmounted.
  551  */
  552 /* ARGSUSED */
  553 static void
  554 acctwatch(void)
  555 {
  556         struct statfs sb;
  557         int vfslocked;
  558 
  559         sx_assert(&acct_sx, SX_XLOCKED);
  560 
  561         /*
  562          * If accounting was disabled before our kthread was scheduled,
  563          * then acct_vp might be NULL.  If so, just ask our kthread to
  564          * exit and return.
  565          */
  566         if (acct_vp == NULL) {
  567                 acct_state |= ACCT_EXITREQ;
  568                 return;
  569         }
  570 
  571         /*
  572          * If our vnode is no longer valid, tear it down and signal the
  573          * accounting thread to die.
  574          */
  575         vfslocked = VFS_LOCK_GIANT(acct_vp->v_mount);
  576         if (acct_vp->v_type == VBAD) {
  577                 (void) acct_disable(NULL);
  578                 VFS_UNLOCK_GIANT(vfslocked);
  579                 acct_state |= ACCT_EXITREQ;
  580                 return;
  581         }
  582 
  583         /*
  584          * Stopping here is better than continuing, maybe it will be VBAD
  585          * next time around.
  586          */
  587         if (VFS_STATFS(acct_vp->v_mount, &sb) < 0) {
  588                 VFS_UNLOCK_GIANT(vfslocked);
  589                 return;
  590         }
  591         VFS_UNLOCK_GIANT(vfslocked);
  592         if (acct_suspended) {
  593                 if (sb.f_bavail > (int64_t)(acctresume * sb.f_blocks /
  594                     100)) {
  595                         acct_suspended = 0;
  596                         log(LOG_NOTICE, "Accounting resumed\n");
  597                 }
  598         } else {
  599                 if (sb.f_bavail <= (int64_t)(acctsuspend * sb.f_blocks /
  600                     100)) {
  601                         acct_suspended = 1;
  602                         log(LOG_NOTICE, "Accounting suspended\n");
  603                 }
  604         }
  605 }
  606 
  607 /*
  608  * The main loop for the dedicated kernel thread that periodically calls
  609  * acctwatch().
  610  */
  611 static void
  612 acct_thread(void *dummy)
  613 {
  614         u_char pri;
  615 
  616         /* This is a low-priority kernel thread. */
  617         pri = PRI_MAX_KERN;
  618         thread_lock(curthread);
  619         sched_prio(curthread, pri);
  620         thread_unlock(curthread);
  621 
  622         /* If another accounting kthread is already running, just die. */
  623         sx_xlock(&acct_sx);
  624         if (acct_state & ACCT_RUNNING) {
  625                 sx_xunlock(&acct_sx);
  626                 kproc_exit(0);
  627         }
  628         acct_state |= ACCT_RUNNING;
  629 
  630         /* Loop until we are asked to exit. */
  631         while (!(acct_state & ACCT_EXITREQ)) {
  632 
  633                 /* Perform our periodic checks. */
  634                 acctwatch();
  635 
  636                 /*
  637                  * We check this flag again before sleeping since the
  638                  * acctwatch() might have shut down accounting and asked us
  639                  * to exit.
  640                  */
  641                 if (!(acct_state & ACCT_EXITREQ)) {
  642                         sx_sleep(&acct_state, &acct_sx, 0, "-",
  643                             acctchkfreq * hz);
  644                 }
  645         }
  646 
  647         /*
  648          * Acknowledge the exit request and shutdown.  We clear both the
  649          * exit request and running flags.
  650          */
  651         acct_state = 0;
  652         sx_xunlock(&acct_sx);
  653         kproc_exit(0);
  654 }

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