fs/afs/flock.c

   1 /* AFS file locking support
   2  *
   3  * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, or (at your option) any later version.
  10  */
  11
  12 #include <linux/smp_lock.h>
  13 #include "internal.h"
  14
  15 #define AFS_LOCK_GRANTED        0
  16 #define AFS_LOCK_PENDING        1
  17
  18 static void afs_fl_copy_lock(struct file_lock *new, struct file_lock *fl);
  19 static void afs_fl_release_private(struct file_lock *fl);
  20
  21 static struct workqueue_struct *afs_lock_manager;
  22 static DEFINE_MUTEX(afs_lock_manager_mutex);
  23
  24 static struct file_lock_operations afs_lock_ops = {
  25         .fl_copy_lock           = afs_fl_copy_lock,
  26         .fl_release_private     = afs_fl_release_private,
  27 };
  28
  29 /*
  30  * initialise the lock manager thread if it isn't already running
  31  */
  32 static int afs_init_lock_manager(void)
  33 {
  34         int ret;
  35
  36         ret = 0;
  37         if (!afs_lock_manager) {
  38                 mutex_lock(&afs_lock_manager_mutex);
  39                 if (!afs_lock_manager) {
  40                         afs_lock_manager =
  41                                 create_singlethread_workqueue("kafs_lockd");
  42                         if (!afs_lock_manager)
  43                                 ret = -ENOMEM;
  44                 }
  45                 mutex_unlock(&afs_lock_manager_mutex);
  46         }
  47         return ret;
  48 }
  49
  50 /*
  51  * destroy the lock manager thread if it's running
  52  */
  53 void __exit afs_kill_lock_manager(void)
  54 {
  55         if (afs_lock_manager)
  56                 destroy_workqueue(afs_lock_manager);
  57 }
  58
  59 /*
  60  * if the callback is broken on this vnode, then the lock may now be available
  61  */
  62 void afs_lock_may_be_available(struct afs_vnode *vnode)
  63 {
  64         _enter("{%x:%u}", vnode->fid.vid, vnode->fid.vnode);
  65
  66         queue_delayed_work(afs_lock_manager, &vnode->lock_work, 0);
  67 }
  68
  69 /*
  70  * the lock will time out in 5 minutes unless we extend it, so schedule
  71  * extension in a bit less than that time
  72  */
  73 static void afs_schedule_lock_extension(struct afs_vnode *vnode)
  74 {
  75         queue_delayed_work(afs_lock_manager, &vnode->lock_work,
  76                            AFS_LOCKWAIT * HZ / 2);
  77 }
  78
  79 /*
  80  * grant one or more locks (readlocks are allowed to jump the queue if the
  81  * first lock in the queue is itself a readlock)
  82  * - the caller must hold the vnode lock
  83  */
  84 static void afs_grant_locks(struct afs_vnode *vnode, struct file_lock *fl)
  85 {
  86         struct file_lock *p, *_p;
  87
  88         list_move_tail(&fl->fl_u.afs.link, &vnode->granted_locks);
  89         if (fl->fl_type == F_RDLCK) {
  90                 list_for_each_entry_safe(p, _p, &vnode->pending_locks,
  91                                          fl_u.afs.link) {
  92                         if (p->fl_type == F_RDLCK) {
  93                                 p->fl_u.afs.state = AFS_LOCK_GRANTED;
  94                                 list_move_tail(&p->fl_u.afs.link,
  95                                                &vnode->granted_locks);
  96                                 wake_up(&p->fl_wait);
  97                         }
  98                 }
  99         }
 100 }
 101
 102 /*
 103  * do work for a lock, including:
 104  * - probing for a lock we're waiting on but didn't get immediately
 105  * - extending a lock that's close to timing out
 106  */
 107 void afs_lock_work(struct work_struct *work)
 108 {
 109         struct afs_vnode *vnode =
 110                 container_of(work, struct afs_vnode, lock_work.work);
 111         struct file_lock *fl;
 112         afs_lock_type_t type;
 113         struct key *key;
 114         int ret;
 115
 116         _enter("{%x:%u}", vnode->fid.vid, vnode->fid.vnode);
 117
 118         spin_lock(&vnode->lock);
 119
 120         if (test_bit(AFS_VNODE_UNLOCKING, &vnode->flags)) {
 121                 _debug("unlock");
 122                 spin_unlock(&vnode->lock);
 123
 124                 /* attempt to release the server lock; if it fails, we just
 125                  * wait 5 minutes and it'll time out anyway */
 126                 ret = afs_vnode_release_lock(vnode, vnode->unlock_key);
 127                 if (ret < 0)
 128                         printk(KERN_WARNING "AFS:"
 129                                " Failed to release lock on {%x:%x} error %d\n",
 130                                vnode->fid.vid, vnode->fid.vnode, ret);
 131
 132                 spin_lock(&vnode->lock);
 133                 key_put(vnode->unlock_key);
 134                 vnode->unlock_key = NULL;
 135                 clear_bit(AFS_VNODE_UNLOCKING, &vnode->flags);
 136         }
 137
 138         /* if we've got a lock, then it must be time to extend that lock as AFS
 139          * locks time out after 5 minutes */
 140         if (!list_empty(&vnode->granted_locks)) {
 141                 _debug("extend");
 142
 143                 if (test_and_set_bit(AFS_VNODE_LOCKING, &vnode->flags))
 144                         BUG();
 145                 fl = list_entry(vnode->granted_locks.next,
 146                                 struct file_lock, fl_u.afs.link);
 147                 key = key_get(fl->fl_file->private_data);
 148                 spin_unlock(&vnode->lock);
 149
 150                 ret = afs_vnode_extend_lock(vnode, key);
 151                 clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
 152                 key_put(key);
 153                 switch (ret) {
 154                 case 0:
 155                         afs_schedule_lock_extension(vnode);
 156                         break;
 157                 default:
 158                         /* ummm... we failed to extend the lock - retry
 159                          * extension shortly */
 160                         printk(KERN_WARNING "AFS:"
 161                                " Failed to extend lock on {%x:%x} error %d\n",
 162                                vnode->fid.vid, vnode->fid.vnode, ret);
 163                         queue_delayed_work(afs_lock_manager, &vnode->lock_work,
 164                                            HZ * 10);
 165                         break;
 166                 }
 167                 _leave(" [extend]");
 168                 return;
 169         }
 170
 171         /* if we don't have a granted lock, then we must've been called back by
 172          * the server, and so if might be possible to get a lock we're
 173          * currently waiting for */
 174         if (!list_empty(&vnode->pending_locks)) {
 175                 _debug("get");
 176
 177                 if (test_and_set_bit(AFS_VNODE_LOCKING, &vnode->flags))
 178                         BUG();
 179                 fl = list_entry(vnode->pending_locks.next,
 180                                 struct file_lock, fl_u.afs.link);
 181                 key = key_get(fl->fl_file->private_data);
 182                 type = (fl->fl_type == F_RDLCK) ?
 183                         AFS_LOCK_READ : AFS_LOCK_WRITE;
 184                 spin_unlock(&vnode->lock);
 185
 186                 ret = afs_vnode_set_lock(vnode, key, type);
 187                 clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
 188                 switch (ret) {
 189                 case -EWOULDBLOCK:
 190                         _debug("blocked");
 191                         break;
 192                 case 0:
 193                         _debug("acquired");
 194                         if (type == AFS_LOCK_READ)
 195                                 set_bit(AFS_VNODE_READLOCKED, &vnode->flags);
 196                         else
 197                                 set_bit(AFS_VNODE_WRITELOCKED, &vnode->flags);
 198                         ret = AFS_LOCK_GRANTED;
 199                 default:
 200                         spin_lock(&vnode->lock);
 201                         /* the pending lock may have been withdrawn due to a
 202                          * signal */
 203                         if (list_entry(vnode->pending_locks.next,
 204                                        struct file_lock, fl_u.afs.link) == fl) {
 205                                 fl->fl_u.afs.state = ret;
 206                                 if (ret == AFS_LOCK_GRANTED)
 207                                         afs_grant_locks(vnode, fl);
 208                                 else
 209                                         list_del_init(&fl->fl_u.afs.link);
 210                                 wake_up(&fl->fl_wait);
 211                                 spin_unlock(&vnode->lock);
 212                         } else {
 213                                 _debug("withdrawn");
 214                                 clear_bit(AFS_VNODE_READLOCKED, &vnode->flags);
 215                                 clear_bit(AFS_VNODE_WRITELOCKED, &vnode->flags);
 216                                 spin_unlock(&vnode->lock);
 217                                 afs_vnode_release_lock(vnode, key);
 218                                 if (!list_empty(&vnode->pending_locks))
 219                                         afs_lock_may_be_available(vnode);
 220                         }
 221                         break;
 222                 }
 223                 key_put(key);
 224                 _leave(" [pend]");
 225                 return;
 226         }
 227
 228         /* looks like the lock request was withdrawn on a signal */
 229         spin_unlock(&vnode->lock);
 230         _leave(" [no locks]");
 231 }
 232
 233 /*
 234  * pass responsibility for the unlocking of a vnode on the server to the
 235  * manager thread, lest a pending signal in the calling thread interrupt
 236  * AF_RXRPC
 237  * - the caller must hold the vnode lock
 238  */
 239 static void afs_defer_unlock(struct afs_vnode *vnode, struct key *key)
 240 {
 241         cancel_delayed_work(&vnode->lock_work);
 242         if (!test_and_clear_bit(AFS_VNODE_READLOCKED, &vnode->flags) &&
 243             !test_and_clear_bit(AFS_VNODE_WRITELOCKED, &vnode->flags))
 244                 BUG();
 245         if (test_and_set_bit(AFS_VNODE_UNLOCKING, &vnode->flags))
 246                 BUG();
 247         vnode->unlock_key = key_get(key);
 248         afs_lock_may_be_available(vnode);
 249 }
 250
 251 /*
 252  * request a lock on a file on the server
 253  */
 254 static int afs_do_setlk(struct file *file, struct file_lock *fl)
 255 {
 256         struct afs_vnode *vnode = AFS_FS_I(file->f_mapping->host);
 257         afs_lock_type_t type;
 258         struct key *key = file->private_data;
 259         int ret;
 260
 261         _enter("{%x:%u},%u", vnode->fid.vid, vnode->fid.vnode, fl->fl_type);
 262
 263         /* only whole-file locks are supported */
 264         if (fl->fl_start != 0 || fl->fl_end != OFFSET_MAX)
 265                 return -EINVAL;
 266
 267         ret = afs_init_lock_manager();
 268         if (ret < 0)
 269                 return ret;
 270
 271         fl->fl_ops = &afs_lock_ops;
 272         INIT_LIST_HEAD(&fl->fl_u.afs.link);
 273         fl->fl_u.afs.state = AFS_LOCK_PENDING;
 274
 275         type = (fl->fl_type == F_RDLCK) ? AFS_LOCK_READ : AFS_LOCK_WRITE;
 276
 277         lock_kernel();
 278
 279         /* make sure we've got a callback on this file and that our view of the
 280          * data version is up to date */
 281         ret = afs_vnode_fetch_status(vnode, NULL, key);
 282         if (ret < 0)
 283                 goto error;
 284
 285         if (vnode->status.lock_count != 0 && !(fl->fl_flags & FL_SLEEP)) {
 286                 ret = -EAGAIN;
 287                 goto error;
 288         }
 289
 290         spin_lock(&vnode->lock);
 291
 292         /* if we've already got a readlock on the server then we can instantly
 293          * grant another readlock, irrespective of whether there are any
 294          * pending writelocks */
 295         if (type == AFS_LOCK_READ &&
 296             vnode->flags & (1 << AFS_VNODE_READLOCKED)) {
 297                 _debug("instant readlock");
 298                 ASSERTCMP(vnode->flags &
 299                           ((1 << AFS_VNODE_LOCKING) |
 300                            (1 << AFS_VNODE_WRITELOCKED)), ==, 0);
 301                 ASSERT(!list_empty(&vnode->granted_locks));
 302                 goto sharing_existing_lock;
 303         }
 304
 305         /* if there's no-one else with a lock on this vnode, then we need to
 306          * ask the server for a lock */
 307         if (list_empty(&vnode->pending_locks) &&
 308             list_empty(&vnode->granted_locks)) {
 309                 _debug("not locked");
 310                 ASSERTCMP(vnode->flags &
 311                           ((1 << AFS_VNODE_LOCKING) |
 312                            (1 << AFS_VNODE_READLOCKED) |
 313                            (1 << AFS_VNODE_WRITELOCKED)), ==, 0);
 314                 list_add_tail(&fl->fl_u.afs.link, &vnode->pending_locks);
 315                 set_bit(AFS_VNODE_LOCKING, &vnode->flags);
 316                 spin_unlock(&vnode->lock);
 317
 318                 ret = afs_vnode_set_lock(vnode, key, type);
 319                 clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
 320                 switch (ret) {
 321                 case 0:
 322                         _debug("acquired");
 323                         goto acquired_server_lock;
 324                 case -EWOULDBLOCK:
 325                         _debug("would block");
 326                         spin_lock(&vnode->lock);
 327                         ASSERT(list_empty(&vnode->granted_locks));
 328                         ASSERTCMP(vnode->pending_locks.next, ==,
 329                                   &fl->fl_u.afs.link);
 330                         goto wait;
 331                 default:
 332                         spin_lock(&vnode->lock);
 333                         list_del_init(&fl->fl_u.afs.link);
 334                         spin_unlock(&vnode->lock);
 335                         goto error;
 336                 }
 337         }
 338
 339         /* otherwise, we need to wait for a local lock to become available */
 340         _debug("wait local");
 341         list_add_tail(&fl->fl_u.afs.link, &vnode->pending_locks);
 342 wait:
 343         if (!(fl->fl_flags & FL_SLEEP)) {
 344                 _debug("noblock");
 345                 ret = -EAGAIN;
 346                 goto abort_attempt;
 347         }
 348         spin_unlock(&vnode->lock);
 349
 350         /* now we need to sleep and wait for the lock manager thread to get the
 351          * lock from the server */
 352         _debug("sleep");
 353         ret = wait_event_interruptible(fl->fl_wait,
 354                                        fl->fl_u.afs.state <= AFS_LOCK_GRANTED);
 355         if (fl->fl_u.afs.state <= AFS_LOCK_GRANTED) {
 356                 ret = fl->fl_u.afs.state;
 357                 if (ret < 0)
 358                         goto error;
 359                 spin_lock(&vnode->lock);
 360                 goto given_lock;
 361         }
 362
 363         /* we were interrupted, but someone may still be in the throes of
 364          * giving us the lock */
 365         _debug("intr");
 366         ASSERTCMP(ret, ==, -ERESTARTSYS);
 367
 368         spin_lock(&vnode->lock);
 369         if (fl->fl_u.afs.state <= AFS_LOCK_GRANTED) {
 370                 ret = fl->fl_u.afs.state;
 371                 if (ret < 0) {
 372                         spin_unlock(&vnode->lock);
 373                         goto error;
 374                 }
 375                 goto given_lock;
 376         }
 377
 378 abort_attempt:
 379         /* we aren't going to get the lock, either because we're unwilling to
 380          * wait, or because some signal happened */
 381         _debug("abort");
 382         if (list_empty(&vnode->granted_locks) &&
 383             vnode->pending_locks.next == &fl->fl_u.afs.link) {
 384                 if (vnode->pending_locks.prev != &fl->fl_u.afs.link) {
 385                         /* kick the next pending lock into having a go */
 386                         list_del_init(&fl->fl_u.afs.link);
 387                         afs_lock_may_be_available(vnode);
 388                 }
 389         } else {
 390                 list_del_init(&fl->fl_u.afs.link);
 391         }
 392         spin_unlock(&vnode->lock);
 393         goto error;
 394
 395 acquired_server_lock:
 396         /* we've acquired a server lock, but it needs to be renewed after 5
 397          * mins */
 398         spin_lock(&vnode->lock);
 399         afs_schedule_lock_extension(vnode);
 400         if (type == AFS_LOCK_READ)
 401                 set_bit(AFS_VNODE_READLOCKED, &vnode->flags);
 402         else
 403                 set_bit(AFS_VNODE_WRITELOCKED, &vnode->flags);
 404 sharing_existing_lock:
 405         /* the lock has been granted as far as we're concerned... */
 406         fl->fl_u.afs.state = AFS_LOCK_GRANTED;
 407         list_move_tail(&fl->fl_u.afs.link, &vnode->granted_locks);
 408 given_lock:
 409         /* ... but we do still need to get the VFS's blessing */
 410         ASSERT(!(vnode->flags & (1 << AFS_VNODE_LOCKING)));
 411         ASSERT((vnode->flags & ((1 << AFS_VNODE_READLOCKED) |
 412                                 (1 << AFS_VNODE_WRITELOCKED))) != 0);
 413         ret = posix_lock_file(file, fl, NULL);
 414         if (ret < 0)
 415                 goto vfs_rejected_lock;
 416         spin_unlock(&vnode->lock);
 417
 418         /* again, make sure we've got a callback on this file and, again, make
 419          * sure that our view of the data version is up to date (we ignore
 420          * errors incurred here and deal with the consequences elsewhere) */
 421         afs_vnode_fetch_status(vnode, NULL, key);
 422
 423 error:
 424         unlock_kernel();
 425         _leave(" = %d", ret);
 426         return ret;
 427
 428 vfs_rejected_lock:
 429         /* the VFS rejected the lock we just obtained, so we have to discard
 430          * what we just got */
 431         _debug("vfs refused %d", ret);
 432         list_del_init(&fl->fl_u.afs.link);
 433         if (list_empty(&vnode->granted_locks))
 434                 afs_defer_unlock(vnode, key);
 435         spin_unlock(&vnode->lock);
 436         goto abort_attempt;
 437 }
 438
 439 /*
 440  * unlock on a file on the server
 441  */
 442 static int afs_do_unlk(struct file *file, struct file_lock *fl)
 443 {
 444         struct afs_vnode *vnode = AFS_FS_I(file->f_mapping->host);
 445         struct key *key = file->private_data;
 446         int ret;
 447
 448         _enter("{%x:%u},%u", vnode->fid.vid, vnode->fid.vnode, fl->fl_type);
 449
 450         /* only whole-file unlocks are supported */
 451         if (fl->fl_start != 0 || fl->fl_end != OFFSET_MAX)
 452                 return -EINVAL;
 453
 454         fl->fl_ops = &afs_lock_ops;
 455         INIT_LIST_HEAD(&fl->fl_u.afs.link);
 456         fl->fl_u.afs.state = AFS_LOCK_PENDING;
 457
 458         spin_lock(&vnode->lock);
 459         ret = posix_lock_file(file, fl, NULL);
 460         if (ret < 0) {
 461                 spin_unlock(&vnode->lock);
 462                 _leave(" = %d [vfs]", ret);
 463                 return ret;
 464         }
 465
 466         /* discard the server lock only if all granted locks are gone */
 467         if (list_empty(&vnode->granted_locks))
 468                 afs_defer_unlock(vnode, key);
 469         spin_unlock(&vnode->lock);
 470         _leave(" = 0");
 471         return 0;
 472 }
 473
 474 /*
 475  * return information about a lock we currently hold, if indeed we hold one
 476  */
 477 static int afs_do_getlk(struct file *file, struct file_lock *fl)
 478 {
 479         struct afs_vnode *vnode = AFS_FS_I(file->f_mapping->host);
 480         struct key *key = file->private_data;
 481         int ret, lock_count;
 482
 483         _enter("");
 484
 485         fl->fl_type = F_UNLCK;
 486
 487         mutex_lock(&vnode->vfs_inode.i_mutex);
 488
 489         /* check local lock records first */
 490         ret = 0;
 491         posix_test_lock(file, fl);
 492         if (fl->fl_type == F_UNLCK) {
 493                 /* no local locks; consult the server */
 494                 ret = afs_vnode_fetch_status(vnode, NULL, key);
 495                 if (ret < 0)
 496                         goto error;
 497                 lock_count = vnode->status.lock_count;
 498                 if (lock_count) {
 499                         if (lock_count > 0)
 500                                 fl->fl_type = F_RDLCK;
 501                         else
 502                                 fl->fl_type = F_WRLCK;
 503                         fl->fl_start = 0;
 504                         fl->fl_end = OFFSET_MAX;
 505                 }
 506         }
 507
 508 error:
 509         mutex_unlock(&vnode->vfs_inode.i_mutex);
 510         _leave(" = %d [%hd]", ret, fl->fl_type);
 511         return ret;
 512 }
 513
 514 /*
 515  * manage POSIX locks on a file
 516  */
 517 int afs_lock(struct file *file, int cmd, struct file_lock *fl)
 518 {
 519         struct afs_vnode *vnode = AFS_FS_I(file->f_dentry->d_inode);
 520
 521         _enter("{%x:%u},%d,{t=%x,fl=%x,r=%Ld:%Ld}",
 522                vnode->fid.vid, vnode->fid.vnode, cmd,
 523                fl->fl_type, fl->fl_flags,
 524                (long long) fl->fl_start, (long long) fl->fl_end);
 525
 526         /* AFS doesn't support mandatory locks */
 527         if (__mandatory_lock(&vnode->vfs_inode) && fl->fl_type != F_UNLCK)
 528                 return -ENOLCK;
 529
 530         if (IS_GETLK(cmd))
 531                 return afs_do_getlk(file, fl);
 532         if (fl->fl_type == F_UNLCK)
 533                 return afs_do_unlk(file, fl);
 534         return afs_do_setlk(file, fl);
 535 }
 536
 537 /*
 538  * manage FLOCK locks on a file
 539  */
 540 int afs_flock(struct file *file, int cmd, struct file_lock *fl)
 541 {
 542         struct afs_vnode *vnode = AFS_FS_I(file->f_dentry->d_inode);
 543
 544         _enter("{%x:%u},%d,{t=%x,fl=%x}",
 545                vnode->fid.vid, vnode->fid.vnode, cmd,
 546                fl->fl_type, fl->fl_flags);
 547
 548         /*
 549          * No BSD flocks over NFS allowed.
 550          * Note: we could try to fake a POSIX lock request here by
 551          * using ((u32) filp | 0x80000000) or some such as the pid.
 552          * Not sure whether that would be unique, though, or whether
 553          * that would break in other places.
 554          */
 555         if (!(fl->fl_flags & FL_FLOCK))
 556                 return -ENOLCK;
 557
 558         /* we're simulating flock() locks using posix locks on the server */
 559         fl->fl_owner = (fl_owner_t) file;
 560         fl->fl_start = 0;
 561         fl->fl_end = OFFSET_MAX;
 562
 563         if (fl->fl_type == F_UNLCK)
 564                 return afs_do_unlk(file, fl);
 565         return afs_do_setlk(file, fl);
 566 }
 567
 568 /*
 569  * the POSIX lock management core VFS code copies the lock record and adds the
 570  * copy into its own list, so we need to add that copy to the vnode's lock
 571  * queue in the same place as the original (which will be deleted shortly
 572  * after)
 573  */
 574 static void afs_fl_copy_lock(struct file_lock *new, struct file_lock *fl)
 575 {
 576         _enter("");
 577
 578         list_add(&new->fl_u.afs.link, &fl->fl_u.afs.link);
 579 }
 580
 581 /*
 582  * need to remove this lock from the vnode queue when it's removed from the
 583  * VFS's list
 584  */
 585 static void afs_fl_release_private(struct file_lock *fl)
 586 {
 587         _enter("");
 588
 589         list_del_init(&fl->fl_u.afs.link);
 590 }