fs/autofs/expire.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright 1997-1998 Transmeta Corporation -- All Rights Reserved
   4  * Copyright 1999-2000 Jeremy Fitzhardinge <jeremy@goop.org>
   5  * Copyright 2001-2006 Ian Kent <raven@themaw.net>
   6  */
   7
   8 #include "autofs_i.h"
   9
  10 /* Check if a dentry can be expired */
  11 static inline int autofs_can_expire(struct dentry *dentry,
  12                                     unsigned long timeout, unsigned int how)
  13 {
  14         struct autofs_info *ino = autofs_dentry_ino(dentry);
  15
  16         /* dentry in the process of being deleted */
  17         if (ino == NULL)
  18                 return 0;
  19
  20         if (!(how & AUTOFS_EXP_IMMEDIATE)) {
  21                 /* Too young to die */
  22                 if (!timeout || time_after(ino->last_used + timeout, jiffies))
  23                         return 0;
  24         }
  25         return 1;
  26 }
  27
  28 /* Check a mount point for busyness */
  29 static int autofs_mount_busy(struct vfsmount *mnt,
  30                              struct dentry *dentry, unsigned int how)
  31 {
  32         struct dentry *top = dentry;
  33         struct path path = {.mnt = mnt, .dentry = dentry};
  34         int status = 1;
  35
  36         pr_debug("dentry %p %pd\n", dentry, dentry);
  37
  38         path_get(&path);
  39
  40         if (!follow_down_one(&path))
  41                 goto done;
  42
  43         if (is_autofs_dentry(path.dentry)) {
  44                 struct autofs_sb_info *sbi = autofs_sbi(path.dentry->d_sb);
  45
  46                 /* This is an autofs submount, we can't expire it */
  47                 if (autofs_type_indirect(sbi->type))
  48                         goto done;
  49         }
  50
  51         /* Not a submount, has a forced expire been requested */
  52         if (how & AUTOFS_EXP_FORCED) {
  53                 status = 0;
  54                 goto done;
  55         }
  56
  57         /* Update the expiry counter if fs is busy */
  58         if (!may_umount_tree(path.mnt)) {
  59                 struct autofs_info *ino;
  60
  61                 ino = autofs_dentry_ino(top);
  62                 ino->last_used = jiffies;
  63                 goto done;
  64         }
  65
  66         status = 0;
  67 done:
  68         pr_debug("returning = %d\n", status);
  69         path_put(&path);
  70         return status;
  71 }
  72
  73 /* p->d_lock held */
  74 static struct dentry *positive_after(struct dentry *p, struct dentry *child)
  75 {
  76         if (child)
  77                 child = list_next_entry(child, d_child);
  78         else
  79                 child = list_first_entry(&p->d_subdirs, struct dentry, d_child);
  80
  81         list_for_each_entry_from(child, &p->d_subdirs, d_child) {
  82                 spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
  83                 if (simple_positive(child)) {
  84                         dget_dlock(child);
  85                         spin_unlock(&child->d_lock);
  86                         return child;
  87                 }
  88                 spin_unlock(&child->d_lock);
  89         }
  90
  91         return NULL;
  92 }
  93
  94 /*
  95  * Calculate and dget next entry in the subdirs list under root.
  96  */
  97 static struct dentry *get_next_positive_subdir(struct dentry *prev,
  98                                                struct dentry *root)
  99 {
 100         struct autofs_sb_info *sbi = autofs_sbi(root->d_sb);
 101         struct dentry *q;
 102
 103         spin_lock(&sbi->lookup_lock);
 104         spin_lock(&root->d_lock);
 105         q = positive_after(root, prev);
 106         spin_unlock(&root->d_lock);
 107         spin_unlock(&sbi->lookup_lock);
 108         dput(prev);
 109         return q;
 110 }
 111
 112 /*
 113  * Calculate and dget next entry in top down tree traversal.
 114  */
 115 static struct dentry *get_next_positive_dentry(struct dentry *prev,
 116                                                struct dentry *root)
 117 {
 118         struct autofs_sb_info *sbi = autofs_sbi(root->d_sb);
 119         struct dentry *p = prev, *ret = NULL, *d = NULL;
 120
 121         if (prev == NULL)
 122                 return dget(root);
 123
 124         spin_lock(&sbi->lookup_lock);
 125         spin_lock(&p->d_lock);
 126         while (1) {
 127                 struct dentry *parent;
 128
 129                 ret = positive_after(p, d);
 130                 if (ret || p == root)
 131                         break;
 132                 parent = p->d_parent;
 133                 spin_unlock(&p->d_lock);
 134                 spin_lock(&parent->d_lock);
 135                 d = p;
 136                 p = parent;
 137         }
 138         spin_unlock(&p->d_lock);
 139         spin_unlock(&sbi->lookup_lock);
 140         dput(prev);
 141         return ret;
 142 }
 143
 144 /*
 145  * Check a direct mount point for busyness.
 146  * Direct mounts have similar expiry semantics to tree mounts.
 147  * The tree is not busy iff no mountpoints are busy and there are no
 148  * autofs submounts.
 149  */
 150 static int autofs_direct_busy(struct vfsmount *mnt,
 151                               struct dentry *top,
 152                               unsigned long timeout,
 153                               unsigned int how)
 154 {
 155         pr_debug("top %p %pd\n", top, top);
 156
 157         /* Forced expire, user space handles busy mounts */
 158         if (how & AUTOFS_EXP_FORCED)
 159                 return 0;
 160
 161         /* If it's busy update the expiry counters */
 162         if (!may_umount_tree(mnt)) {
 163                 struct autofs_info *ino;
 164
 165                 ino = autofs_dentry_ino(top);
 166                 if (ino)
 167                         ino->last_used = jiffies;
 168                 return 1;
 169         }
 170
 171         /* Timeout of a direct mount is determined by its top dentry */
 172         if (!autofs_can_expire(top, timeout, how))
 173                 return 1;
 174
 175         return 0;
 176 }
 177
 178 /*
 179  * Check a directory tree of mount points for busyness
 180  * The tree is not busy iff no mountpoints are busy
 181  */
 182 static int autofs_tree_busy(struct vfsmount *mnt,
 183                             struct dentry *top,
 184                             unsigned long timeout,
 185                             unsigned int how)
 186 {
 187         struct autofs_info *top_ino = autofs_dentry_ino(top);
 188         struct dentry *p;
 189
 190         pr_debug("top %p %pd\n", top, top);
 191
 192         /* Negative dentry - give up */
 193         if (!simple_positive(top))
 194                 return 1;
 195
 196         p = NULL;
 197         while ((p = get_next_positive_dentry(p, top))) {
 198                 pr_debug("dentry %p %pd\n", p, p);
 199
 200                 /*
 201                  * Is someone visiting anywhere in the subtree ?
 202                  * If there's no mount we need to check the usage
 203                  * count for the autofs dentry.
 204                  * If the fs is busy update the expiry counter.
 205                  */
 206                 if (d_mountpoint(p)) {
 207                         if (autofs_mount_busy(mnt, p, how)) {
 208                                 top_ino->last_used = jiffies;
 209                                 dput(p);
 210                                 return 1;
 211                         }
 212                 } else {
 213                         struct autofs_info *ino = autofs_dentry_ino(p);
 214                         unsigned int ino_count = READ_ONCE(ino->count);
 215
 216                         /* allow for dget above and top is already dgot */
 217                         if (p == top)
 218                                 ino_count += 2;
 219                         else
 220                                 ino_count++;
 221
 222                         if (d_count(p) > ino_count) {
 223                                 top_ino->last_used = jiffies;
 224                                 dput(p);
 225                                 return 1;
 226                         }
 227                 }
 228         }
 229
 230         /* Forced expire, user space handles busy mounts */
 231         if (how & AUTOFS_EXP_FORCED)
 232                 return 0;
 233
 234         /* Timeout of a tree mount is ultimately determined by its top dentry */
 235         if (!autofs_can_expire(top, timeout, how))
 236                 return 1;
 237
 238         return 0;
 239 }
 240
 241 static struct dentry *autofs_check_leaves(struct vfsmount *mnt,
 242                                           struct dentry *parent,
 243                                           unsigned long timeout,
 244                                           unsigned int how)
 245 {
 246         struct dentry *p;
 247
 248         pr_debug("parent %p %pd\n", parent, parent);
 249
 250         p = NULL;
 251         while ((p = get_next_positive_dentry(p, parent))) {
 252                 pr_debug("dentry %p %pd\n", p, p);
 253
 254                 if (d_mountpoint(p)) {
 255                         /* Can we umount this guy */
 256                         if (autofs_mount_busy(mnt, p, how))
 257                                 continue;
 258
 259                         /* This isn't a submount so if a forced expire
 260                          * has been requested, user space handles busy
 261                          * mounts */
 262                         if (how & AUTOFS_EXP_FORCED)
 263                                 return p;
 264
 265                         /* Can we expire this guy */
 266                         if (autofs_can_expire(p, timeout, how))
 267                                 return p;
 268                 }
 269         }
 270         return NULL;
 271 }
 272
 273 /* Check if we can expire a direct mount (possibly a tree) */
 274 static struct dentry *autofs_expire_direct(struct super_block *sb,
 275                                            struct vfsmount *mnt,
 276                                            struct autofs_sb_info *sbi,
 277                                            unsigned int how)
 278 {
 279         struct dentry *root = dget(sb->s_root);
 280         struct autofs_info *ino;
 281         unsigned long timeout;
 282
 283         if (!root)
 284                 return NULL;
 285
 286         timeout = sbi->exp_timeout;
 287
 288         if (!autofs_direct_busy(mnt, root, timeout, how)) {
 289                 spin_lock(&sbi->fs_lock);
 290                 ino = autofs_dentry_ino(root);
 291                 /* No point expiring a pending mount */
 292                 if (ino->flags & AUTOFS_INF_PENDING) {
 293                         spin_unlock(&sbi->fs_lock);
 294                         goto out;
 295                 }
 296                 ino->flags |= AUTOFS_INF_WANT_EXPIRE;
 297                 spin_unlock(&sbi->fs_lock);
 298                 synchronize_rcu();
 299                 if (!autofs_direct_busy(mnt, root, timeout, how)) {
 300                         spin_lock(&sbi->fs_lock);
 301                         ino->flags |= AUTOFS_INF_EXPIRING;
 302                         init_completion(&ino->expire_complete);
 303                         spin_unlock(&sbi->fs_lock);
 304                         return root;
 305                 }
 306                 spin_lock(&sbi->fs_lock);
 307                 ino->flags &= ~AUTOFS_INF_WANT_EXPIRE;
 308                 spin_unlock(&sbi->fs_lock);
 309         }
 310 out:
 311         dput(root);
 312
 313         return NULL;
 314 }
 315
 316 /* Check if 'dentry' should expire, or return a nearby
 317  * dentry that is suitable.
 318  * If returned dentry is different from arg dentry,
 319  * then a dget() reference was taken, else not.
 320  */
 321 static struct dentry *should_expire(struct dentry *dentry,
 322                                     struct vfsmount *mnt,
 323                                     unsigned long timeout,
 324                                     unsigned int how)
 325 {
 326         struct autofs_info *ino = autofs_dentry_ino(dentry);
 327         unsigned int ino_count;
 328
 329         /* No point expiring a pending mount */
 330         if (ino->flags & AUTOFS_INF_PENDING)
 331                 return NULL;
 332
 333         /*
 334          * Case 1: (i) indirect mount or top level pseudo direct mount
 335          *         (autofs-4.1).
 336          *         (ii) indirect mount with offset mount, check the "/"
 337          *         offset (autofs-5.0+).
 338          */
 339         if (d_mountpoint(dentry)) {
 340                 pr_debug("checking mountpoint %p %pd\n", dentry, dentry);
 341
 342                 /* Can we umount this guy */
 343                 if (autofs_mount_busy(mnt, dentry, how))
 344                         return NULL;
 345
 346                 /* This isn't a submount so if a forced expire
 347                  * has been requested, user space handles busy
 348                  * mounts */
 349                 if (how & AUTOFS_EXP_FORCED)
 350                         return dentry;
 351
 352                 /* Can we expire this guy */
 353                 if (autofs_can_expire(dentry, timeout, how))
 354                         return dentry;
 355                 return NULL;
 356         }
 357
 358         if (d_is_symlink(dentry)) {
 359                 pr_debug("checking symlink %p %pd\n", dentry, dentry);
 360
 361                 /* Forced expire, user space handles busy mounts */
 362                 if (how & AUTOFS_EXP_FORCED)
 363                         return dentry;
 364
 365                 /*
 366                  * A symlink can't be "busy" in the usual sense so
 367                  * just check last used for expire timeout.
 368                  */
 369                 if (autofs_can_expire(dentry, timeout, how))
 370                         return dentry;
 371                 return NULL;
 372         }
 373
 374         if (simple_empty(dentry))
 375                 return NULL;
 376
 377         /* Case 2: tree mount, expire iff entire tree is not busy */
 378         if (!(how & AUTOFS_EXP_LEAVES)) {
 379                 /* Not a forced expire? */
 380                 if (!(how & AUTOFS_EXP_FORCED)) {
 381                         /* ref-walk currently on this dentry? */
 382                         ino_count = READ_ONCE(ino->count) + 1;
 383                         if (d_count(dentry) > ino_count)
 384                                 return NULL;
 385                 }
 386
 387                 if (!autofs_tree_busy(mnt, dentry, timeout, how))
 388                         return dentry;
 389         /*
 390          * Case 3: pseudo direct mount, expire individual leaves
 391          *         (autofs-4.1).
 392          */
 393         } else {
 394                 struct dentry *expired;
 395
 396                 /* Not a forced expire? */
 397                 if (!(how & AUTOFS_EXP_FORCED)) {
 398                         /* ref-walk currently on this dentry? */
 399                         ino_count = READ_ONCE(ino->count) + 1;
 400                         if (d_count(dentry) > ino_count)
 401                                 return NULL;
 402                 }
 403
 404                 expired = autofs_check_leaves(mnt, dentry, timeout, how);
 405                 if (expired) {
 406                         if (expired == dentry)
 407                                 dput(dentry);
 408                         return expired;
 409                 }
 410         }
 411         return NULL;
 412 }
 413
 414 /*
 415  * Find an eligible tree to time-out
 416  * A tree is eligible if :-
 417  *  - it is unused by any user process
 418  *  - it has been unused for exp_timeout time
 419  */
 420 static struct dentry *autofs_expire_indirect(struct super_block *sb,
 421                                              struct vfsmount *mnt,
 422                                              struct autofs_sb_info *sbi,
 423                                              unsigned int how)
 424 {
 425         unsigned long timeout;
 426         struct dentry *root = sb->s_root;
 427         struct dentry *dentry;
 428         struct dentry *expired;
 429         struct dentry *found;
 430         struct autofs_info *ino;
 431
 432         if (!root)
 433                 return NULL;
 434
 435         timeout = sbi->exp_timeout;
 436
 437         dentry = NULL;
 438         while ((dentry = get_next_positive_subdir(dentry, root))) {
 439                 spin_lock(&sbi->fs_lock);
 440                 ino = autofs_dentry_ino(dentry);
 441                 if (ino->flags & AUTOFS_INF_WANT_EXPIRE) {
 442                         spin_unlock(&sbi->fs_lock);
 443                         continue;
 444                 }
 445                 spin_unlock(&sbi->fs_lock);
 446
 447                 expired = should_expire(dentry, mnt, timeout, how);
 448                 if (!expired)
 449                         continue;
 450
 451                 spin_lock(&sbi->fs_lock);
 452                 ino = autofs_dentry_ino(expired);
 453                 ino->flags |= AUTOFS_INF_WANT_EXPIRE;
 454                 spin_unlock(&sbi->fs_lock);
 455                 synchronize_rcu();
 456
 457                 /* Make sure a reference is not taken on found if
 458                  * things have changed.
 459                  */
 460                 how &= ~AUTOFS_EXP_LEAVES;
 461                 found = should_expire(expired, mnt, timeout, how);
 462                 if (found != expired) { // something has changed, continue
 463                         dput(found);
 464                         goto next;
 465                 }
 466
 467                 if (expired != dentry)
 468                         dput(dentry);
 469
 470                 spin_lock(&sbi->fs_lock);
 471                 goto found;
 472 next:
 473                 spin_lock(&sbi->fs_lock);
 474                 ino->flags &= ~AUTOFS_INF_WANT_EXPIRE;
 475                 spin_unlock(&sbi->fs_lock);
 476                 if (expired != dentry)
 477                         dput(expired);
 478         }
 479         return NULL;
 480
 481 found:
 482         pr_debug("returning %p %pd\n", expired, expired);
 483         ino->flags |= AUTOFS_INF_EXPIRING;
 484         init_completion(&ino->expire_complete);
 485         spin_unlock(&sbi->fs_lock);
 486         return expired;
 487 }
 488
 489 int autofs_expire_wait(const struct path *path, int rcu_walk)
 490 {
 491         struct dentry *dentry = path->dentry;
 492         struct autofs_sb_info *sbi = autofs_sbi(dentry->d_sb);
 493         struct autofs_info *ino = autofs_dentry_ino(dentry);
 494         int status;
 495         int state;
 496
 497         /* Block on any pending expire */
 498         if (!(ino->flags & AUTOFS_INF_WANT_EXPIRE))
 499                 return 0;
 500         if (rcu_walk)
 501                 return -ECHILD;
 502
 503 retry:
 504         spin_lock(&sbi->fs_lock);
 505         state = ino->flags & (AUTOFS_INF_WANT_EXPIRE | AUTOFS_INF_EXPIRING);
 506         if (state == AUTOFS_INF_WANT_EXPIRE) {
 507                 spin_unlock(&sbi->fs_lock);
 508                 /*
 509                  * Possibly being selected for expire, wait until
 510                  * it's selected or not.
 511                  */
 512                 schedule_timeout_uninterruptible(HZ/10);
 513                 goto retry;
 514         }
 515         if (state & AUTOFS_INF_EXPIRING) {
 516                 spin_unlock(&sbi->fs_lock);
 517
 518                 pr_debug("waiting for expire %p name=%pd\n", dentry, dentry);
 519
 520                 status = autofs_wait(sbi, path, NFY_NONE);
 521                 wait_for_completion(&ino->expire_complete);
 522
 523                 pr_debug("expire done status=%d\n", status);
 524
 525                 if (d_unhashed(dentry))
 526                         return -EAGAIN;
 527
 528                 return status;
 529         }
 530         spin_unlock(&sbi->fs_lock);
 531
 532         return 0;
 533 }
 534
 535 /* Perform an expiry operation */
 536 int autofs_expire_run(struct super_block *sb,
 537                       struct vfsmount *mnt,
 538                       struct autofs_sb_info *sbi,
 539                       struct autofs_packet_expire __user *pkt_p)
 540 {
 541         struct autofs_packet_expire pkt;
 542         struct autofs_info *ino;
 543         struct dentry *dentry;
 544         int ret = 0;
 545
 546         memset(&pkt, 0, sizeof(pkt));
 547
 548         pkt.hdr.proto_version = sbi->version;
 549         pkt.hdr.type = autofs_ptype_expire;
 550
 551         dentry = autofs_expire_indirect(sb, mnt, sbi, 0);
 552         if (!dentry)
 553                 return -EAGAIN;
 554
 555         pkt.len = dentry->d_name.len;
 556         memcpy(pkt.name, dentry->d_name.name, pkt.len);
 557         pkt.name[pkt.len] = '\0';
 558
 559         if (copy_to_user(pkt_p, &pkt, sizeof(struct autofs_packet_expire)))
 560                 ret = -EFAULT;
 561
 562         spin_lock(&sbi->fs_lock);
 563         ino = autofs_dentry_ino(dentry);
 564         /* avoid rapid-fire expire attempts if expiry fails */
 565         ino->last_used = jiffies;
 566         ino->flags &= ~(AUTOFS_INF_EXPIRING|AUTOFS_INF_WANT_EXPIRE);
 567         complete_all(&ino->expire_complete);
 568         spin_unlock(&sbi->fs_lock);
 569
 570         dput(dentry);
 571
 572         return ret;
 573 }
 574
 575 int autofs_do_expire_multi(struct super_block *sb, struct vfsmount *mnt,
 576                            struct autofs_sb_info *sbi, unsigned int how)
 577 {
 578         struct dentry *dentry;
 579         int ret = -EAGAIN;
 580
 581         if (autofs_type_trigger(sbi->type))
 582                 dentry = autofs_expire_direct(sb, mnt, sbi, how);
 583         else
 584                 dentry = autofs_expire_indirect(sb, mnt, sbi, how);
 585
 586         if (dentry) {
 587                 struct autofs_info *ino = autofs_dentry_ino(dentry);
 588                 const struct path path = { .mnt = mnt, .dentry = dentry };
 589
 590                 /* This is synchronous because it makes the daemon a
 591                  * little easier
 592                  */
 593                 ret = autofs_wait(sbi, &path, NFY_EXPIRE);
 594
 595                 spin_lock(&sbi->fs_lock);
 596                 /* avoid rapid-fire expire attempts if expiry fails */
 597                 ino->last_used = jiffies;
 598                 ino->flags &= ~(AUTOFS_INF_EXPIRING|AUTOFS_INF_WANT_EXPIRE);
 599                 complete_all(&ino->expire_complete);
 600                 spin_unlock(&sbi->fs_lock);
 601                 dput(dentry);
 602         }
 603
 604         return ret;
 605 }
 606
 607 /*
 608  * Call repeatedly until it returns -EAGAIN, meaning there's nothing
 609  * more to be done.
 610  */
 611 int autofs_expire_multi(struct super_block *sb, struct vfsmount *mnt,
 612                         struct autofs_sb_info *sbi, int __user *arg)
 613 {
 614         unsigned int how = 0;
 615
 616         if (arg && get_user(how, arg))
 617                 return -EFAULT;
 618
 619         return autofs_do_expire_multi(sb, mnt, sbi, how);
 620 }