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