fs/lockd/svclock.c

   1 /*
   2  * linux/fs/lockd/svclock.c
   3  *
   4  * Handling of server-side locks, mostly of the blocked variety.
   5  * This is the ugliest part of lockd because we tread on very thin ice.
   6  * GRANT and CANCEL calls may get stuck, meet in mid-flight, etc.
   7  * IMNSHO introducing the grant callback into the NLM protocol was one
   8  * of the worst ideas Sun ever had. Except maybe for the idea of doing
   9  * NFS file locking at all.
  10  *
  11  * I'm trying hard to avoid race conditions by protecting most accesses
  12  * to a file's list of blocked locks through a semaphore. The global
  13  * list of blocked locks is not protected in this fashion however.
  14  * Therefore, some functions (such as the RPC callback for the async grant
  15  * call) move blocked locks towards the head of the list *while some other
  16  * process might be traversing it*. This should not be a problem in
  17  * practice, because this will only cause functions traversing the list
  18  * to visit some blocks twice.
  19  *
  20  * Copyright (C) 1996, Olaf Kirch <okir@monad.swb.de>
  21  */
  22
  23 #include <linux/config.h>
  24 #include <linux/types.h>
  25 #include <linux/errno.h>
  26 #include <linux/kernel.h>
  27 #include <linux/sched.h>
  28 #include <linux/smp_lock.h>
  29 #include <linux/sunrpc/clnt.h>
  30 #include <linux/sunrpc/svc.h>
  31 #include <linux/lockd/nlm.h>
  32 #include <linux/lockd/lockd.h>
  33
  34 #define NLMDBG_FACILITY         NLMDBG_SVCLOCK
  35
  36 #ifdef CONFIG_LOCKD_V4
  37 #define nlm_deadlock    nlm4_deadlock
  38 #else
  39 #define nlm_deadlock    nlm_lck_denied
  40 #endif
  41
  42 static void     nlmsvc_insert_block(struct nlm_block *block, unsigned long);
  43 static int      nlmsvc_remove_block(struct nlm_block *block);
  44 static void     nlmsvc_grant_callback(struct rpc_task *task);
  45 static void     nlmsvc_notify_blocked(struct file_lock *);
  46
  47 /*
  48  * The list of blocked locks to retry
  49  */
  50 static struct nlm_block *       nlm_blocked;
  51
  52 /*
  53  * Insert a blocked lock into the global list
  54  */
  55 static void
  56 nlmsvc_insert_block(struct nlm_block *block, unsigned long when)
  57 {
  58         struct nlm_block **bp, *b;
  59
  60         dprintk("lockd: nlmsvc_insert_block(%p, %ld)\n", block, when);
  61         if (block->b_queued)
  62                 nlmsvc_remove_block(block);
  63         bp = &nlm_blocked;
  64         if (when != NLM_NEVER) {
  65                 if ((when += jiffies) == NLM_NEVER)
  66                         when ++;
  67                 while ((b = *bp) && time_before_eq(b->b_when,when))
  68                         bp = &b->b_next;
  69         } else
  70                 while ((b = *bp))
  71                         bp = &b->b_next;
  72
  73         block->b_queued = 1;
  74         block->b_when = when;
  75         block->b_next = b;
  76         *bp = block;
  77 }
  78
  79 /*
  80  * Remove a block from the global list
  81  */
  82 static int
  83 nlmsvc_remove_block(struct nlm_block *block)
  84 {
  85         struct nlm_block **bp, *b;
  86
  87         if (!block->b_queued)
  88                 return 1;
  89         for (bp = &nlm_blocked; (b = *bp); bp = &b->b_next) {
  90                 if (b == block) {
  91                         *bp = block->b_next;
  92                         block->b_queued = 0;
  93                         return 1;
  94                 }
  95         }
  96
  97         return 0;
  98 }
  99
 100 /*
 101  * Find a block for a given lock and optionally remove it from
 102  * the list.
 103  */
 104 static struct nlm_block *
 105 nlmsvc_lookup_block(struct nlm_file *file, struct nlm_lock *lock, int remove)
 106 {
 107         struct nlm_block        **head, *block;
 108         struct file_lock        *fl;
 109
 110         dprintk("lockd: nlmsvc_lookup_block f=%p pd=%d %Ld-%Ld ty=%d\n",
 111                                 file, lock->fl.fl_pid,
 112                                 (long long)lock->fl.fl_start,
 113                                 (long long)lock->fl.fl_end, lock->fl.fl_type);
 114         for (head = &nlm_blocked; (block = *head); head = &block->b_next) {
 115                 fl = &block->b_call.a_args.lock.fl;
 116                 dprintk("lockd: check f=%p pd=%d %Ld-%Ld ty=%d cookie=%x\n",
 117                                 block->b_file, fl->fl_pid,
 118                                 (long long)fl->fl_start,
 119                                 (long long)fl->fl_end, fl->fl_type,
 120                                 *(unsigned int*)(block->b_call.a_args.cookie.data));
 121                 if (block->b_file == file && nlm_compare_locks(fl, &lock->fl)) {
 122                         if (remove) {
 123                                 *head = block->b_next;
 124                                 block->b_queued = 0;
 125                         }
 126                         return block;
 127                 }
 128         }
 129
 130         return NULL;
 131 }
 132
 133 static inline int nlm_cookie_match(struct nlm_cookie *a, struct nlm_cookie *b)
 134 {
 135         if(a->len != b->len)
 136                 return 0;
 137         if(memcmp(a->data,b->data,a->len))
 138                 return 0;
 139         return 1;
 140 }
 141
 142 /*
 143  * Find a block with a given NLM cookie.
 144  */
 145 static inline struct nlm_block *
 146 nlmsvc_find_block(struct nlm_cookie *cookie)
 147 {
 148         struct nlm_block *block;
 149
 150         for (block = nlm_blocked; block; block = block->b_next) {
 151                 dprintk("cookie: head of blocked queue %p, block %p\n",
 152                         nlm_blocked, block);
 153                 if (nlm_cookie_match(&block->b_call.a_args.cookie,cookie))
 154                         break;
 155         }
 156
 157         return block;
 158 }
 159
 160 /*
 161  * Create a block and initialize it.
 162  *
 163  * Note: we explicitly set the cookie of the grant reply to that of
 164  * the blocked lock request. The spec explicitly mentions that the client
 165  * should _not_ rely on the callback containing the same cookie as the
 166  * request, but (as I found out later) that's because some implementations
 167  * do just this. Never mind the standards comittees, they support our
 168  * logging industries.
 169  */
 170 static inline struct nlm_block *
 171 nlmsvc_create_block(struct svc_rqst *rqstp, struct nlm_file *file,
 172                                 struct nlm_lock *lock, struct nlm_cookie *cookie)
 173 {
 174         struct nlm_block        *block;
 175         struct nlm_host         *host;
 176         struct nlm_rqst         *call;
 177
 178         /* Create host handle for callback */
 179         host = nlmclnt_lookup_host(&rqstp->rq_addr,
 180                                 rqstp->rq_prot, rqstp->rq_vers);
 181         if (host == NULL)
 182                 return NULL;
 183
 184         /* Allocate memory for block, and initialize arguments */
 185         if (!(block = (struct nlm_block *) kmalloc(sizeof(*block), GFP_KERNEL)))
 186                 goto failed;
 187         memset(block, 0, sizeof(*block));
 188         locks_init_lock(&block->b_call.a_args.lock.fl);
 189         locks_init_lock(&block->b_call.a_res.lock.fl);
 190
 191         if (!nlmclnt_setgrantargs(&block->b_call, lock))
 192                 goto failed_free;
 193
 194         /* Set notifier function for VFS, and init args */
 195         block->b_call.a_args.lock.fl.fl_notify = nlmsvc_notify_blocked;
 196         block->b_call.a_args.cookie = *cookie;  /* see above */
 197
 198         dprintk("lockd: created block %p...\n", block);
 199
 200         /* Create and initialize the block */
 201         block->b_daemon = rqstp->rq_server;
 202         block->b_host   = host;
 203         block->b_file   = file;
 204
 205         /* Add to file's list of blocks */
 206         block->b_fnext  = file->f_blocks;
 207         file->f_blocks  = block;
 208
 209         /* Set up RPC arguments for callback */
 210         call = &block->b_call;
 211         call->a_host    = host;
 212         call->a_flags   = RPC_TASK_ASYNC;
 213
 214         return block;
 215
 216 failed_free:
 217         kfree(block);
 218 failed:
 219         nlm_release_host(host);
 220         return NULL;
 221 }
 222
 223 /*
 224  * Delete a block. If the lock was cancelled or the grant callback
 225  * failed, unlock is set to 1.
 226  * It is the caller's responsibility to check whether the file
 227  * can be closed hereafter.
 228  */
 229 static void
 230 nlmsvc_delete_block(struct nlm_block *block, int unlock)
 231 {
 232         struct file_lock        *fl = &block->b_call.a_args.lock.fl;
 233         struct nlm_file         *file = block->b_file;
 234         struct nlm_block        **bp;
 235
 236         dprintk("lockd: deleting block %p...\n", block);
 237
 238         /* Remove block from list */
 239         nlmsvc_remove_block(block);
 240
 241         /* If granted, unlock it, else remove from inode block list */
 242         if (unlock && block->b_granted) {
 243                 dprintk("lockd: deleting granted lock\n");
 244                 fl->fl_type = F_UNLCK;
 245                 posix_lock_file(&block->b_file->f_file, fl, 0);
 246                 block->b_granted = 0;
 247         } else {
 248                 dprintk("lockd: unblocking blocked lock\n");
 249                 posix_unblock_lock(fl);
 250         }
 251
 252         /* If the block is in the middle of a GRANT callback,
 253          * don't kill it yet. */
 254         if (block->b_incall) {
 255                 nlmsvc_insert_block(block, NLM_NEVER);
 256                 block->b_done = 1;
 257                 return;
 258         }
 259
 260         /* Remove block from file's list of blocks */
 261         for (bp = &file->f_blocks; *bp; bp = &(*bp)->b_fnext) {
 262                 if (*bp == block) {
 263                         *bp = block->b_fnext;
 264                         break;
 265                 }
 266         }
 267
 268         if (block->b_host)
 269                 nlm_release_host(block->b_host);
 270         nlmclnt_freegrantargs(&block->b_call);
 271         kfree(block);
 272 }
 273
 274 /*
 275  * Loop over all blocks and perform the action specified.
 276  * (NLM_ACT_CHECK handled by nlmsvc_inspect_file).
 277  */
 278 int
 279 nlmsvc_traverse_blocks(struct nlm_host *host, struct nlm_file *file, int action)
 280 {
 281         struct nlm_block        *block, *next;
 282
 283         down(&file->f_sema);
 284         for (block = file->f_blocks; block; block = next) {
 285                 next = block->b_fnext;
 286                 if (action == NLM_ACT_MARK)
 287                         block->b_host->h_inuse = 1;
 288                 else if (action == NLM_ACT_UNLOCK) {
 289                         if (host == NULL || host == block->b_host)
 290                                 nlmsvc_delete_block(block, 1);
 291                 }
 292         }
 293         up(&file->f_sema);
 294         return 0;
 295 }
 296
 297 /*
 298  * Attempt to establish a lock, and if it can't be granted, block it
 299  * if required.
 300  */
 301 u32
 302 nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
 303                         struct nlm_lock *lock, int wait, struct nlm_cookie *cookie)
 304 {
 305         struct file_lock        *conflock;
 306         struct nlm_block        *block;
 307         int                     error;
 308
 309         dprintk("lockd: nlmsvc_lock(%04x/%ld, ty=%d, pi=%d, %Ld-%Ld, bl=%d)\n",
 310                                 file->f_file.f_dentry->d_inode->i_dev,
 311                                 file->f_file.f_dentry->d_inode->i_ino,
 312                                 lock->fl.fl_type, lock->fl.fl_pid,
 313                                 (long long)lock->fl.fl_start,
 314                                 (long long)lock->fl.fl_end,
 315                                 wait);
 316
 317         /* Lock file against concurrent access */
 318         down(&file->f_sema);
 319
 320         /* Get existing block (in case client is busy-waiting) */
 321         block = nlmsvc_lookup_block(file, lock, 0);
 322
 323         lock->fl.fl_flags |= FL_LOCKD;
 324
 325 again:
 326         if (!(conflock = posix_test_lock(&file->f_file, &lock->fl))) {
 327                 error = posix_lock_file(&file->f_file, &lock->fl, 0);
 328
 329                 if (block)
 330                         nlmsvc_delete_block(block, 0);
 331                 up(&file->f_sema);
 332
 333                 dprintk("lockd: posix_lock_file returned %d\n", -error);
 334                 switch(-error) {
 335                 case 0:
 336                         return nlm_granted;
 337                 case EDEADLK:
 338                         return nlm_deadlock;
 339                 case EAGAIN:
 340                         return nlm_lck_denied;
 341                 default:                        /* includes ENOLCK */
 342                         return nlm_lck_denied_nolocks;
 343                 }
 344         }
 345
 346         if (!wait) {
 347                 up(&file->f_sema);
 348                 return nlm_lck_denied;
 349         }
 350
 351         if (posix_locks_deadlock(&lock->fl, conflock)) {
 352                 up(&file->f_sema);
 353                 return nlm_deadlock;
 354         }
 355
 356         /* If we don't have a block, create and initialize it. Then
 357          * retry because we may have slept in kmalloc. */
 358         if (block == NULL) {
 359                 dprintk("lockd: blocking on this lock (allocating).\n");
 360                 if (!(block = nlmsvc_create_block(rqstp, file, lock, cookie)))
 361                         return nlm_lck_denied_nolocks;
 362                 goto again;
 363         }
 364
 365         /* Append to list of blocked */
 366         nlmsvc_insert_block(block, NLM_NEVER);
 367
 368         if (list_empty(&block->b_call.a_args.lock.fl.fl_block)) {
 369                 /* Now add block to block list of the conflicting lock
 370                    if we haven't done so. */
 371                 dprintk("lockd: blocking on this lock.\n");
 372                 posix_block_lock(conflock, &block->b_call.a_args.lock.fl);
 373         }
 374
 375         up(&file->f_sema);
 376         return nlm_lck_blocked;
 377 }
 378
 379 /*
 380  * Test for presence of a conflicting lock.
 381  */
 382 u32
 383 nlmsvc_testlock(struct nlm_file *file, struct nlm_lock *lock,
 384                                        struct nlm_lock *conflock)
 385 {
 386         struct file_lock        *fl;
 387
 388         dprintk("lockd: nlmsvc_testlock(%04x/%ld, ty=%d, %Ld-%Ld)\n",
 389                                 file->f_file.f_dentry->d_inode->i_dev,
 390                                 file->f_file.f_dentry->d_inode->i_ino,
 391                                 lock->fl.fl_type,
 392                                 (long long)lock->fl.fl_start,
 393                                 (long long)lock->fl.fl_end);
 394
 395         if ((fl = posix_test_lock(&file->f_file, &lock->fl)) != NULL) {
 396                 dprintk("lockd: conflicting lock(ty=%d, %Ld-%Ld)\n",
 397                                 fl->fl_type, (long long)fl->fl_start,
 398                                 (long long)fl->fl_end);
 399                 conflock->caller = "somehost";  /* FIXME */
 400                 conflock->oh.len = 0;           /* don't return OH info */
 401                 conflock->fl = *fl;
 402                 return nlm_lck_denied;
 403         }
 404
 405         return nlm_granted;
 406 }
 407
 408 /*
 409  * Remove a lock.
 410  * This implies a CANCEL call: We send a GRANT_MSG, the client replies
 411  * with a GRANT_RES call which gets lost, and calls UNLOCK immediately
 412  * afterwards. In this case the block will still be there, and hence
 413  * must be removed.
 414  */
 415 u32
 416 nlmsvc_unlock(struct nlm_file *file, struct nlm_lock *lock)
 417 {
 418         int     error;
 419
 420         dprintk("lockd: nlmsvc_unlock(%04x/%ld, pi=%d, %Ld-%Ld)\n",
 421                                 file->f_file.f_dentry->d_inode->i_dev,
 422                                 file->f_file.f_dentry->d_inode->i_ino,
 423                                 lock->fl.fl_pid,
 424                                 (long long)lock->fl.fl_start,
 425                                 (long long)lock->fl.fl_end);
 426
 427         /* First, cancel any lock that might be there */
 428         nlmsvc_cancel_blocked(file, lock);
 429
 430         lock->fl.fl_type = F_UNLCK;
 431         error = posix_lock_file(&file->f_file, &lock->fl, 0);
 432
 433         return (error < 0)? nlm_lck_denied_nolocks : nlm_granted;
 434 }
 435
 436 /*
 437  * Cancel a previously blocked request.
 438  *
 439  * A cancel request always overrides any grant that may currently
 440  * be in progress.
 441  * The calling procedure must check whether the file can be closed.
 442  */
 443 u32
 444 nlmsvc_cancel_blocked(struct nlm_file *file, struct nlm_lock *lock)
 445 {
 446         struct nlm_block        *block;
 447
 448         dprintk("lockd: nlmsvc_cancel(%04x/%ld, pi=%d, %Ld-%Ld)\n",
 449                                 file->f_file.f_dentry->d_inode->i_dev,
 450                                 file->f_file.f_dentry->d_inode->i_ino,
 451                                 lock->fl.fl_pid,
 452                                 (long long)lock->fl.fl_start,
 453                                 (long long)lock->fl.fl_end);
 454
 455         down(&file->f_sema);
 456         if ((block = nlmsvc_lookup_block(file, lock, 1)) != NULL)
 457                 nlmsvc_delete_block(block, 1);
 458         up(&file->f_sema);
 459         return nlm_granted;
 460 }
 461
 462 /*
 463  * Unblock a blocked lock request. This is a callback invoked from the
 464  * VFS layer when a lock on which we blocked is removed.
 465  *
 466  * This function doesn't grant the blocked lock instantly, but rather moves
 467  * the block to the head of nlm_blocked where it can be picked up by lockd.
 468  */
 469 static void
 470 nlmsvc_notify_blocked(struct file_lock *fl)
 471 {
 472         struct nlm_block        **bp, *block;
 473
 474         dprintk("lockd: VFS unblock notification for block %p\n", fl);
 475         posix_unblock_lock(fl);
 476         for (bp = &nlm_blocked; (block = *bp); bp = &block->b_next) {
 477                 if (nlm_compare_locks(&block->b_call.a_args.lock.fl, fl)) {
 478                         nlmsvc_insert_block(block, 0);
 479                         svc_wake_up(block->b_daemon);
 480                         return;
 481                 }
 482         }
 483
 484         printk(KERN_WARNING "lockd: notification for unknown block!\n");
 485 }
 486
 487 /*
 488  * Try to claim a lock that was previously blocked.
 489  *
 490  * Note that we use both the RPC_GRANTED_MSG call _and_ an async
 491  * RPC thread when notifying the client. This seems like overkill...
 492  * Here's why:
 493  *  -   we don't want to use a synchronous RPC thread, otherwise
 494  *      we might find ourselves hanging on a dead portmapper.
 495  *  -   Some lockd implementations (e.g. HP) don't react to
 496  *      RPC_GRANTED calls; they seem to insist on RPC_GRANTED_MSG calls.
 497  */
 498 static void
 499 nlmsvc_grant_blocked(struct nlm_block *block)
 500 {
 501         struct nlm_file         *file = block->b_file;
 502         struct nlm_lock         *lock = &block->b_call.a_args.lock;
 503         struct file_lock        *conflock;
 504         int                     error;
 505
 506         dprintk("lockd: grant blocked lock %p\n", block);
 507
 508         /* First thing is lock the file */
 509         down(&file->f_sema);
 510
 511         /* Unlink block request from list */
 512         nlmsvc_remove_block(block);
 513
 514         /* If b_granted is true this means we've been here before.
 515          * Just retry the grant callback, possibly refreshing the RPC
 516          * binding */
 517         if (block->b_granted) {
 518                 nlm_rebind_host(block->b_host);
 519                 goto callback;
 520         }
 521
 522         /* Try the lock operation again */
 523         if ((conflock = posix_test_lock(&file->f_file, &lock->fl)) != NULL) {
 524                 /* Bummer, we blocked again */
 525                 dprintk("lockd: lock still blocked\n");
 526                 nlmsvc_insert_block(block, NLM_NEVER);
 527                 posix_block_lock(conflock, &lock->fl);
 528                 up(&file->f_sema);
 529                 return;
 530         }
 531
 532         /* Alright, no conflicting lock. Now lock it for real. If the
 533          * following yields an error, this is most probably due to low
 534          * memory. Retry the lock in a few seconds.
 535          */
 536         if ((error = posix_lock_file(&file->f_file, &lock->fl, 0)) < 0) {
 537                 printk(KERN_WARNING "lockd: unexpected error %d in %s!\n",
 538                                 -error, __FUNCTION__);
 539                 nlmsvc_insert_block(block, 10 * HZ);
 540                 up(&file->f_sema);
 541                 return;
 542         }
 543
 544 callback:
 545         /* Lock was granted by VFS. */
 546         dprintk("lockd: GRANTing blocked lock.\n");
 547         block->b_granted = 1;
 548         block->b_incall  = 1;
 549
 550         /* Schedule next grant callback in 30 seconds */
 551         nlmsvc_insert_block(block, 30 * HZ);
 552
 553         /* Call the client */
 554         nlm_get_host(block->b_call.a_host);
 555         if (nlmsvc_async_call(&block->b_call, NLMPROC_GRANTED_MSG,
 556                                                 nlmsvc_grant_callback) < 0)
 557                 nlm_release_host(block->b_call.a_host);
 558         up(&file->f_sema);
 559 }
 560
 561 /*
 562  * This is the callback from the RPC layer when the NLM_GRANTED_MSG
 563  * RPC call has succeeded or timed out.
 564  * Like all RPC callbacks, it is invoked by the rpciod process, so it
 565  * better not sleep. Therefore, we put the blocked lock on the nlm_blocked
 566  * chain once more in order to have it removed by lockd itself (which can
 567  * then sleep on the file semaphore without disrupting e.g. the nfs client).
 568  */
 569 static void
 570 nlmsvc_grant_callback(struct rpc_task *task)
 571 {
 572         struct nlm_rqst         *call = (struct nlm_rqst *) task->tk_calldata;
 573         struct nlm_block        *block;
 574         unsigned long           timeout;
 575
 576         dprintk("lockd: GRANT_MSG RPC callback\n");
 577         dprintk("callback: looking for cookie %x \n",
 578                 *(unsigned int *)(call->a_args.cookie.data));
 579         if (!(block = nlmsvc_find_block(&call->a_args.cookie))) {
 580                 dprintk("lockd: no block for cookie %x\n", *(u32 *)(call->a_args.cookie.data));
 581                 return;
 582         }
 583
 584         /* Technically, we should down the file semaphore here. Since we
 585          * move the block towards the head of the queue only, no harm
 586          * can be done, though. */
 587         if (task->tk_status < 0) {
 588                 /* RPC error: Re-insert for retransmission */
 589                 timeout = 10 * HZ;
 590         } else if (block->b_done) {
 591                 /* Block already removed, kill it for real */
 592                 timeout = 0;
 593         } else {
 594                 /* Call was successful, now wait for client callback */
 595                 timeout = 60 * HZ;
 596         }
 597         nlmsvc_insert_block(block, timeout);
 598         svc_wake_up(block->b_daemon);
 599         block->b_incall = 0;
 600
 601         nlm_release_host(call->a_host);
 602 }
 603
 604 /*
 605  * We received a GRANT_RES callback. Try to find the corresponding
 606  * block.
 607  */
 608 void
 609 nlmsvc_grant_reply(struct nlm_cookie *cookie, u32 status)
 610 {
 611         struct nlm_block        *block;
 612         struct nlm_file         *file;
 613
 614         if (!(block = nlmsvc_find_block(cookie)))
 615                 return;
 616         file = block->b_file;
 617
 618         file->f_count++;
 619         down(&file->f_sema);
 620         if ((block = nlmsvc_find_block(cookie)) != NULL) {
 621                 if (status == NLM_LCK_DENIED_GRACE_PERIOD) {
 622                         /* Try again in a couple of seconds */
 623                         nlmsvc_insert_block(block, 10 * HZ);
 624                         block = NULL;
 625                 } else {
 626                         /* Lock is now held by client, or has been rejected.
 627                          * In both cases, the block should be removed. */
 628                         file->f_count++;
 629                         up(&file->f_sema);
 630                         if (status == NLM_LCK_GRANTED)
 631                                 nlmsvc_delete_block(block, 0);
 632                         else
 633                                 nlmsvc_delete_block(block, 1);
 634                 }
 635         }
 636         if (!block)
 637                 up(&file->f_sema);
 638         nlm_release_file(file);
 639 }
 640
 641 /*
 642  * Retry all blocked locks that have been notified. This is where lockd
 643  * picks up locks that can be granted, or grant notifications that must
 644  * be retransmitted.
 645  */
 646 unsigned long
 647 nlmsvc_retry_blocked(void)
 648 {
 649         struct nlm_block        *block;
 650
 651         dprintk("nlmsvc_retry_blocked(%p, when=%ld)\n",
 652                         nlm_blocked,
 653                         nlm_blocked? nlm_blocked->b_when : 0);
 654         while ((block = nlm_blocked)) {
 655                 if (block->b_when == NLM_NEVER)
 656                         break;
 657                 if (time_after(block->b_when,jiffies))
 658                         break;
 659                 dprintk("nlmsvc_retry_blocked(%p, when=%ld, done=%d)\n",
 660                         block, block->b_when, block->b_done);
 661                 if (block->b_done)
 662                         nlmsvc_delete_block(block, 0);
 663                 else
 664                         nlmsvc_grant_blocked(block);
 665         }
 666
 667         if ((block = nlm_blocked) && block->b_when != NLM_NEVER)
 668                 return (block->b_when - jiffies);
 669
 670         return MAX_SCHEDULE_TIMEOUT;
 671 }