kernel/acct.c

   1 /*
   2  *  linux/kernel/acct.c
   3  *
   4  *  BSD Process Accounting for Linux
   5  *
   6  *  Author: Marco van Wieringen <mvw@planets.elm.net>
   7  *
   8  *  Some code based on ideas and code from:
   9  *  Thomas K. Dyas <tdyas@eden.rutgers.edu>
  10  *
  11  *  This file implements BSD-style process accounting. Whenever any
  12  *  process exits, an accounting record of type "struct acct" is
  13  *  written to the file specified with the acct() system call. It is
  14  *  up to user-level programs to do useful things with the accounting
  15  *  log. The kernel just provides the raw accounting information.
  16  *
  17  * (C) Copyright 1995 - 1997 Marco van Wieringen - ELM Consultancy B.V.
  18  *
  19  *  Plugged two leaks. 1) It didn't return acct_file into the free_filps if
  20  *  the file happened to be read-only. 2) If the accounting was suspended
  21  *  due to the lack of space it happily allowed to reopen it and completely
  22  *  lost the old acct_file. 3/10/98, Al Viro.
  23  *
  24  *  Now we silently close acct_file on attempt to reopen. Cleaned sys_acct().
  25  *  XTerms and EMACS are manifestations of pure evil. 21/10/98, AV.
  26  *
  27  *  Fixed a nasty interaction with with sys_umount(). If the accointing
  28  *  was suspeneded we failed to stop it on umount(). Messy.
  29  *  Another one: remount to readonly didn't stop accounting.
  30  *      Question: what should we do if we have CAP_SYS_ADMIN but not
  31  *  CAP_SYS_PACCT? Current code does the following: umount returns -EBUSY
  32  *  unless we are messing with the root. In that case we are getting a
  33  *  real mess with do_remount_sb(). 9/11/98, AV.
  34  *
  35  *  Fixed a bunch of races (and pair of leaks). Probably not the best way,
  36  *  but this one obviously doesn't introduce deadlocks. Later. BTW, found
  37  *  one race (and leak) in BSD implementation.
  38  *  OK, that's better. ANOTHER race and leak in BSD variant. There always
  39  *  is one more bug... 10/11/98, AV.
  40  *
  41  *      Oh, fsck... Oopsable SMP race in do_process_acct() - we must hold
  42  * ->mmap_sem to walk the vma list of current->mm. Nasty, since it leaks
  43  * a struct file opened for write. Fixed. 2/6/2000, AV.
  44  */
  45
  46 #include <linux/mm.h>
  47 #include <linux/slab.h>
  48 #include <linux/acct.h>
  49 #include <linux/capability.h>
  50 #include <linux/file.h>
  51 #include <linux/tty.h>
  52 #include <linux/security.h>
  53 #include <linux/vfs.h>
  54 #include <linux/jiffies.h>
  55 #include <linux/times.h>
  56 #include <linux/syscalls.h>
  57 #include <linux/mount.h>
  58 #include <asm/uaccess.h>
  59 #include <asm/div64.h>
  60 #include <linux/blkdev.h> /* sector_div */
  61 #include <linux/pid_namespace.h>
  62
  63 /*
  64  * These constants control the amount of freespace that suspend and
  65  * resume the process accounting system, and the time delay between
  66  * each check.
  67  * Turned into sysctl-controllable parameters. AV, 12/11/98
  68  */
  69
  70 int acct_parm[3] = {4, 2, 30};
  71 #define RESUME          (acct_parm[0])  /* >foo% free space - resume */
  72 #define SUSPEND         (acct_parm[1])  /* <foo% free space - suspend */
  73 #define ACCT_TIMEOUT    (acct_parm[2])  /* foo second timeout between checks */
  74
  75 /*
  76  * External references and all of the globals.
  77  */
  78 static void do_acct_process(struct bsd_acct_struct *acct,
  79                 struct pid_namespace *ns, struct file *);
  80
  81 /*
  82  * This structure is used so that all the data protected by lock
  83  * can be placed in the same cache line as the lock.  This primes
  84  * the cache line to have the data after getting the lock.
  85  */
  86 struct bsd_acct_struct {
  87         volatile int            active;
  88         volatile int            needcheck;
  89         struct file             *file;
  90         struct pid_namespace    *ns;
  91         struct timer_list       timer;
  92         struct list_head        list;
  93 };
  94
  95 static DEFINE_SPINLOCK(acct_lock);
  96 static LIST_HEAD(acct_list);
  97
  98 /*
  99  * Called whenever the timer says to check the free space.
 100  */
 101 static void acct_timeout(unsigned long x)
 102 {
 103         struct bsd_acct_struct *acct = (struct bsd_acct_struct *)x;
 104         acct->needcheck = 1;
 105 }
 106
 107 /*
 108  * Check the amount of free space and suspend/resume accordingly.
 109  */
 110 static int check_free_space(struct bsd_acct_struct *acct, struct file *file)
 111 {
 112         struct kstatfs sbuf;
 113         int res;
 114         int act;
 115         sector_t resume;
 116         sector_t suspend;
 117
 118         spin_lock(&acct_lock);
 119         res = acct->active;
 120         if (!file || !acct->needcheck)
 121                 goto out;
 122         spin_unlock(&acct_lock);
 123
 124         /* May block */
 125         if (vfs_statfs(&file->f_path, &sbuf))
 126                 return res;
 127         suspend = sbuf.f_blocks * SUSPEND;
 128         resume = sbuf.f_blocks * RESUME;
 129
 130         sector_div(suspend, 100);
 131         sector_div(resume, 100);
 132
 133         if (sbuf.f_bavail <= suspend)
 134                 act = -1;
 135         else if (sbuf.f_bavail >= resume)
 136                 act = 1;
 137         else
 138                 act = 0;
 139
 140         /*
 141          * If some joker switched acct->file under us we'ld better be
 142          * silent and _not_ touch anything.
 143          */
 144         spin_lock(&acct_lock);
 145         if (file != acct->file) {
 146                 if (act)
 147                         res = act>0;
 148                 goto out;
 149         }
 150
 151         if (acct->active) {
 152                 if (act < 0) {
 153                         acct->active = 0;
 154                         printk(KERN_INFO "Process accounting paused\n");
 155                 }
 156         } else {
 157                 if (act > 0) {
 158                         acct->active = 1;
 159                         printk(KERN_INFO "Process accounting resumed\n");
 160                 }
 161         }
 162
 163         del_timer(&acct->timer);
 164         acct->needcheck = 0;
 165         acct->timer.expires = jiffies + ACCT_TIMEOUT*HZ;
 166         add_timer(&acct->timer);
 167         res = acct->active;
 168 out:
 169         spin_unlock(&acct_lock);
 170         return res;
 171 }
 172
 173 /*
 174  * Close the old accounting file (if currently open) and then replace
 175  * it with file (if non-NULL).
 176  *
 177  * NOTE: acct_lock MUST be held on entry and exit.
 178  */
 179 static void acct_file_reopen(struct bsd_acct_struct *acct, struct file *file,
 180                 struct pid_namespace *ns)
 181 {
 182         struct file *old_acct = NULL;
 183         struct pid_namespace *old_ns = NULL;
 184
 185         if (acct->file) {
 186                 old_acct = acct->file;
 187                 old_ns = acct->ns;
 188                 del_timer(&acct->timer);
 189                 acct->active = 0;
 190                 acct->needcheck = 0;
 191                 acct->file = NULL;
 192                 acct->ns = NULL;
 193                 list_del(&acct->list);
 194         }
 195         if (file) {
 196                 acct->file = file;
 197                 acct->ns = ns;
 198                 acct->needcheck = 0;
 199                 acct->active = 1;
 200                 list_add(&acct->list, &acct_list);
 201                 /* It's been deleted if it was used before so this is safe */
 202                 setup_timer(&acct->timer, acct_timeout, (unsigned long)acct);
 203                 acct->timer.expires = jiffies + ACCT_TIMEOUT*HZ;
 204                 add_timer(&acct->timer);
 205         }
 206         if (old_acct) {
 207                 mnt_unpin(old_acct->f_path.mnt);
 208                 spin_unlock(&acct_lock);
 209                 do_acct_process(acct, old_ns, old_acct);
 210                 filp_close(old_acct, NULL);
 211                 spin_lock(&acct_lock);
 212         }
 213 }
 214
 215 static int acct_on(char *name)
 216 {
 217         struct file *file;
 218         struct vfsmount *mnt;
 219         struct pid_namespace *ns;
 220         struct bsd_acct_struct *acct = NULL;
 221
 222         /* Difference from BSD - they don't do O_APPEND */
 223         file = filp_open(name, O_WRONLY|O_APPEND|O_LARGEFILE, 0);
 224         if (IS_ERR(file))
 225                 return PTR_ERR(file);
 226
 227         if (!S_ISREG(file->f_path.dentry->d_inode->i_mode)) {
 228                 filp_close(file, NULL);
 229                 return -EACCES;
 230         }
 231
 232         if (!file->f_op->write) {
 233                 filp_close(file, NULL);
 234                 return -EIO;
 235         }
 236
 237         ns = task_active_pid_ns(current);
 238         if (ns->bacct == NULL) {
 239                 acct = kzalloc(sizeof(struct bsd_acct_struct), GFP_KERNEL);
 240                 if (acct == NULL) {
 241                         filp_close(file, NULL);
 242                         return -ENOMEM;
 243                 }
 244         }
 245
 246         spin_lock(&acct_lock);
 247         if (ns->bacct == NULL) {
 248                 ns->bacct = acct;
 249                 acct = NULL;
 250         }
 251
 252         mnt = file->f_path.mnt;
 253         mnt_pin(mnt);
 254         acct_file_reopen(ns->bacct, file, ns);
 255         spin_unlock(&acct_lock);
 256
 257         mntput(mnt); /* it's pinned, now give up active reference */
 258         kfree(acct);
 259
 260         return 0;
 261 }
 262
 263 /**
 264  * sys_acct - enable/disable process accounting
 265  * @name: file name for accounting records or NULL to shutdown accounting
 266  *
 267  * Returns 0 for success or negative errno values for failure.
 268  *
 269  * sys_acct() is the only system call needed to implement process
 270  * accounting. It takes the name of the file where accounting records
 271  * should be written. If the filename is NULL, accounting will be
 272  * shutdown.
 273  */
 274 SYSCALL_DEFINE1(acct, const char __user *, name)
 275 {
 276         int error = 0;
 277
 278         if (!capable(CAP_SYS_PACCT))
 279                 return -EPERM;
 280
 281         if (name) {
 282                 char *tmp = getname(name);
 283                 if (IS_ERR(tmp))
 284                         return (PTR_ERR(tmp));
 285                 error = acct_on(tmp);
 286                 putname(tmp);
 287         } else {
 288                 struct bsd_acct_struct *acct;
 289
 290                 acct = task_active_pid_ns(current)->bacct;
 291                 if (acct == NULL)
 292                         return 0;
 293
 294                 spin_lock(&acct_lock);
 295                 acct_file_reopen(acct, NULL, NULL);
 296                 spin_unlock(&acct_lock);
 297         }
 298
 299         return error;
 300 }
 301
 302 /**
 303  * acct_auto_close - turn off a filesystem's accounting if it is on
 304  * @m: vfsmount being shut down
 305  *
 306  * If the accounting is turned on for a file in the subtree pointed to
 307  * to by m, turn accounting off.  Done when m is about to die.
 308  */
 309 void acct_auto_close_mnt(struct vfsmount *m)
 310 {
 311         struct bsd_acct_struct *acct;
 312
 313         spin_lock(&acct_lock);
 314 restart:
 315         list_for_each_entry(acct, &acct_list, list)
 316                 if (acct->file && acct->file->f_path.mnt == m) {
 317                         acct_file_reopen(acct, NULL, NULL);
 318                         goto restart;
 319                 }
 320         spin_unlock(&acct_lock);
 321 }
 322
 323 /**
 324  * acct_auto_close - turn off a filesystem's accounting if it is on
 325  * @sb: super block for the filesystem
 326  *
 327  * If the accounting is turned on for a file in the filesystem pointed
 328  * to by sb, turn accounting off.
 329  */
 330 void acct_auto_close(struct super_block *sb)
 331 {
 332         struct bsd_acct_struct *acct;
 333
 334         spin_lock(&acct_lock);
 335 restart:
 336         list_for_each_entry(acct, &acct_list, list)
 337                 if (acct->file && acct->file->f_path.mnt->mnt_sb == sb) {
 338                         acct_file_reopen(acct, NULL, NULL);
 339                         goto restart;
 340                 }
 341         spin_unlock(&acct_lock);
 342 }
 343
 344 void acct_exit_ns(struct pid_namespace *ns)
 345 {
 346         struct bsd_acct_struct *acct = ns->bacct;
 347
 348         if (acct == NULL)
 349                 return;
 350
 351         del_timer_sync(&acct->timer);
 352         spin_lock(&acct_lock);
 353         if (acct->file != NULL)
 354                 acct_file_reopen(acct, NULL, NULL);
 355         spin_unlock(&acct_lock);
 356
 357         kfree(acct);
 358 }
 359
 360 /*
 361  *  encode an unsigned long into a comp_t
 362  *
 363  *  This routine has been adopted from the encode_comp_t() function in
 364  *  the kern_acct.c file of the FreeBSD operating system. The encoding
 365  *  is a 13-bit fraction with a 3-bit (base 8) exponent.
 366  */
 367
 368 #define MANTSIZE        13                      /* 13 bit mantissa. */
 369 #define EXPSIZE         3                       /* Base 8 (3 bit) exponent. */
 370 #define MAXFRACT        ((1 << MANTSIZE) - 1)   /* Maximum fractional value. */
 371
 372 static comp_t encode_comp_t(unsigned long value)
 373 {
 374         int exp, rnd;
 375
 376         exp = rnd = 0;
 377         while (value > MAXFRACT) {
 378                 rnd = value & (1 << (EXPSIZE - 1));     /* Round up? */
 379                 value >>= EXPSIZE;      /* Base 8 exponent == 3 bit shift. */
 380                 exp++;
 381         }
 382
 383         /*
 384          * If we need to round up, do it (and handle overflow correctly).
 385          */
 386         if (rnd && (++value > MAXFRACT)) {
 387                 value >>= EXPSIZE;
 388                 exp++;
 389         }
 390
 391         /*
 392          * Clean it up and polish it off.
 393          */
 394         exp <<= MANTSIZE;               /* Shift the exponent into place */
 395         exp += value;                   /* and add on the mantissa. */
 396         return exp;
 397 }
 398
 399 #if ACCT_VERSION==1 || ACCT_VERSION==2
 400 /*
 401  * encode an u64 into a comp2_t (24 bits)
 402  *
 403  * Format: 5 bit base 2 exponent, 20 bits mantissa.
 404  * The leading bit of the mantissa is not stored, but implied for
 405  * non-zero exponents.
 406  * Largest encodable value is 50 bits.
 407  */
 408
 409 #define MANTSIZE2       20                      /* 20 bit mantissa. */
 410 #define EXPSIZE2        5                       /* 5 bit base 2 exponent. */
 411 #define MAXFRACT2       ((1ul << MANTSIZE2) - 1) /* Maximum fractional value. */
 412 #define MAXEXP2         ((1 <<EXPSIZE2) - 1)    /* Maximum exponent. */
 413
 414 static comp2_t encode_comp2_t(u64 value)
 415 {
 416         int exp, rnd;
 417
 418         exp = (value > (MAXFRACT2>>1));
 419         rnd = 0;
 420         while (value > MAXFRACT2) {
 421                 rnd = value & 1;
 422                 value >>= 1;
 423                 exp++;
 424         }
 425
 426         /*
 427          * If we need to round up, do it (and handle overflow correctly).
 428          */
 429         if (rnd && (++value > MAXFRACT2)) {
 430                 value >>= 1;
 431                 exp++;
 432         }
 433
 434         if (exp > MAXEXP2) {
 435                 /* Overflow. Return largest representable number instead. */
 436                 return (1ul << (MANTSIZE2+EXPSIZE2-1)) - 1;
 437         } else {
 438                 return (value & (MAXFRACT2>>1)) | (exp << (MANTSIZE2-1));
 439         }
 440 }
 441 #endif
 442
 443 #if ACCT_VERSION==3
 444 /*
 445  * encode an u64 into a 32 bit IEEE float
 446  */
 447 static u32 encode_float(u64 value)
 448 {
 449         unsigned exp = 190;
 450         unsigned u;
 451
 452         if (value==0) return 0;
 453         while ((s64)value > 0){
 454                 value <<= 1;
 455                 exp--;
 456         }
 457         u = (u32)(value >> 40) & 0x7fffffu;
 458         return u | (exp << 23);
 459 }
 460 #endif
 461
 462 /*
 463  *  Write an accounting entry for an exiting process
 464  *
 465  *  The acct_process() call is the workhorse of the process
 466  *  accounting system. The struct acct is built here and then written
 467  *  into the accounting file. This function should only be called from
 468  *  do_exit() or when switching to a different output file.
 469  */
 470
 471 /*
 472  *  do_acct_process does all actual work. Caller holds the reference to file.
 473  */
 474 static void do_acct_process(struct bsd_acct_struct *acct,
 475                 struct pid_namespace *ns, struct file *file)
 476 {
 477         struct pacct_struct *pacct = &current->signal->pacct;
 478         acct_t ac;
 479         mm_segment_t fs;
 480         unsigned long flim;
 481         u64 elapsed;
 482         u64 run_time;
 483         struct timespec uptime;
 484         struct tty_struct *tty;
 485         const struct cred *orig_cred;
 486
 487         /* Perform file operations on behalf of whoever enabled accounting */
 488         orig_cred = override_creds(file->f_cred);
 489
 490         /*
 491          * First check to see if there is enough free_space to continue
 492          * the process accounting system.
 493          */
 494         if (!check_free_space(acct, file))
 495                 goto out;
 496
 497         /*
 498          * Fill the accounting struct with the needed info as recorded
 499          * by the different kernel functions.
 500          */
 501         memset((caddr_t)&ac, 0, sizeof(acct_t));
 502
 503         ac.ac_version = ACCT_VERSION | ACCT_BYTEORDER;
 504         strlcpy(ac.ac_comm, current->comm, sizeof(ac.ac_comm));
 505
 506         /* calculate run_time in nsec*/
 507         do_posix_clock_monotonic_gettime(&uptime);
 508         run_time = (u64)uptime.tv_sec*NSEC_PER_SEC + uptime.tv_nsec;
 509         run_time -= (u64)current->group_leader->start_time.tv_sec * NSEC_PER_SEC
 510                        + current->group_leader->start_time.tv_nsec;
 511         /* convert nsec -> AHZ */
 512         elapsed = nsec_to_AHZ(run_time);
 513 #if ACCT_VERSION==3
 514         ac.ac_etime = encode_float(elapsed);
 515 #else
 516         ac.ac_etime = encode_comp_t(elapsed < (unsigned long) -1l ?
 517                                (unsigned long) elapsed : (unsigned long) -1l);
 518 #endif
 519 #if ACCT_VERSION==1 || ACCT_VERSION==2
 520         {
 521                 /* new enlarged etime field */
 522                 comp2_t etime = encode_comp2_t(elapsed);
 523                 ac.ac_etime_hi = etime >> 16;
 524                 ac.ac_etime_lo = (u16) etime;
 525         }
 526 #endif
 527         do_div(elapsed, AHZ);
 528         ac.ac_btime = get_seconds() - elapsed;
 529         /* we really need to bite the bullet and change layout */
 530         ac.ac_uid = orig_cred->uid;
 531         ac.ac_gid = orig_cred->gid;
 532 #if ACCT_VERSION==2
 533         ac.ac_ahz = AHZ;
 534 #endif
 535 #if ACCT_VERSION==1 || ACCT_VERSION==2
 536         /* backward-compatible 16 bit fields */
 537         ac.ac_uid16 = ac.ac_uid;
 538         ac.ac_gid16 = ac.ac_gid;
 539 #endif
 540 #if ACCT_VERSION==3
 541         ac.ac_pid = task_tgid_nr_ns(current, ns);
 542         rcu_read_lock();
 543         ac.ac_ppid = task_tgid_nr_ns(rcu_dereference(current->real_parent), ns);
 544         rcu_read_unlock();
 545 #endif
 546
 547         spin_lock_irq(&current->sighand->siglock);
 548         tty = current->signal->tty;     /* Safe as we hold the siglock */
 549         ac.ac_tty = tty ? old_encode_dev(tty_devnum(tty)) : 0;
 550         ac.ac_utime = encode_comp_t(jiffies_to_AHZ(cputime_to_jiffies(pacct->ac_utime)));
 551         ac.ac_stime = encode_comp_t(jiffies_to_AHZ(cputime_to_jiffies(pacct->ac_stime)));
 552         ac.ac_flag = pacct->ac_flag;
 553         ac.ac_mem = encode_comp_t(pacct->ac_mem);
 554         ac.ac_minflt = encode_comp_t(pacct->ac_minflt);
 555         ac.ac_majflt = encode_comp_t(pacct->ac_majflt);
 556         ac.ac_exitcode = pacct->ac_exitcode;
 557         spin_unlock_irq(&current->sighand->siglock);
 558         ac.ac_io = encode_comp_t(0 /* current->io_usage */);    /* %% */
 559         ac.ac_rw = encode_comp_t(ac.ac_io / 1024);
 560         ac.ac_swaps = encode_comp_t(0);
 561
 562         /*
 563          * Kernel segment override to datasegment and write it
 564          * to the accounting file.
 565          */
 566         fs = get_fs();
 567         set_fs(KERNEL_DS);
 568         /*
 569          * Accounting records are not subject to resource limits.
 570          */
 571         flim = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
 572         current->signal->rlim[RLIMIT_FSIZE].rlim_cur = RLIM_INFINITY;
 573         file->f_op->write(file, (char *)&ac,
 574                                sizeof(acct_t), &file->f_pos);
 575         current->signal->rlim[RLIMIT_FSIZE].rlim_cur = flim;
 576         set_fs(fs);
 577 out:
 578         revert_creds(orig_cred);
 579 }
 580
 581 /**
 582  * acct_collect - collect accounting information into pacct_struct
 583  * @exitcode: task exit code
 584  * @group_dead: not 0, if this thread is the last one in the process.
 585  */
 586 void acct_collect(long exitcode, int group_dead)
 587 {
 588         struct pacct_struct *pacct = &current->signal->pacct;
 589         unsigned long vsize = 0;
 590
 591         if (group_dead && current->mm) {
 592                 struct vm_area_struct *vma;
 593                 down_read(&current->mm->mmap_sem);
 594                 vma = current->mm->mmap;
 595                 while (vma) {
 596                         vsize += vma->vm_end - vma->vm_start;
 597                         vma = vma->vm_next;
 598                 }
 599                 up_read(&current->mm->mmap_sem);
 600         }
 601
 602         spin_lock_irq(&current->sighand->siglock);
 603         if (group_dead)
 604                 pacct->ac_mem = vsize / 1024;
 605         if (thread_group_leader(current)) {
 606                 pacct->ac_exitcode = exitcode;
 607                 if (current->flags & PF_FORKNOEXEC)
 608                         pacct->ac_flag |= AFORK;
 609         }
 610         if (current->flags & PF_SUPERPRIV)
 611                 pacct->ac_flag |= ASU;
 612         if (current->flags & PF_DUMPCORE)
 613                 pacct->ac_flag |= ACORE;
 614         if (current->flags & PF_SIGNALED)
 615                 pacct->ac_flag |= AXSIG;
 616         pacct->ac_utime = cputime_add(pacct->ac_utime, current->utime);
 617         pacct->ac_stime = cputime_add(pacct->ac_stime, current->stime);
 618         pacct->ac_minflt += current->min_flt;
 619         pacct->ac_majflt += current->maj_flt;
 620         spin_unlock_irq(&current->sighand->siglock);
 621 }
 622
 623 static void acct_process_in_ns(struct pid_namespace *ns)
 624 {
 625         struct file *file = NULL;
 626         struct bsd_acct_struct *acct;
 627
 628         acct = ns->bacct;
 629         /*
 630          * accelerate the common fastpath:
 631          */
 632         if (!acct || !acct->file)
 633                 return;
 634
 635         spin_lock(&acct_lock);
 636         file = acct->file;
 637         if (unlikely(!file)) {
 638                 spin_unlock(&acct_lock);
 639                 return;
 640         }
 641         get_file(file);
 642         spin_unlock(&acct_lock);
 643
 644         do_acct_process(acct, ns, file);
 645         fput(file);
 646 }
 647
 648 /**
 649  * acct_process - now just a wrapper around acct_process_in_ns,
 650  * which in turn is a wrapper around do_acct_process.
 651  *
 652  * handles process accounting for an exiting task
 653  */
 654 void acct_process(void)
 655 {
 656         struct pid_namespace *ns;
 657
 658         /*
 659          * This loop is safe lockless, since current is still
 660          * alive and holds its namespace, which in turn holds
 661          * its parent.
 662          */
 663         for (ns = task_active_pid_ns(current); ns != NULL; ns = ns->parent)
 664                 acct_process_in_ns(ns);
 665 }