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 45 static const struct rpc_call_ops nlmsvc_grant_ops; 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) && b->b_when != NLM_NEVER) 68 bp = &b->b_next; 69 } else 70 while ((b = *bp) != 0) 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) != 0; 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) != 0; 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=%s\n", 117 block->b_file, fl->fl_pid, 118 (long long)fl->fl_start, 119 (long long)fl->fl_end, fl->fl_type, 120 nlmdbg_cookie2a(&block->b_call.a_args.cookie)); 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, struct sockaddr_in *sin) 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 && nlm_cmp_addr(sin, &block->b_host->h_addr)) 155 break; 156 } 157 158 return block; 159 } 160 161 /* 162 * Create a block and initialize it. 163 * 164 * Note: we explicitly set the cookie of the grant reply to that of 165 * the blocked lock request. The spec explicitly mentions that the client 166 * should _not_ rely on the callback containing the same cookie as the 167 * request, but (as I found out later) that's because some implementations 168 * do just this. Never mind the standards comittees, they support our 169 * logging industries. 170 */ 171 static inline struct nlm_block * 172 nlmsvc_create_block(struct svc_rqst *rqstp, struct nlm_file *file, 173 struct nlm_lock *lock, struct nlm_cookie *cookie) 174 { 175 struct nlm_block *block; 176 struct nlm_host *host; 177 struct nlm_rqst *call; 178 179 /* Create host handle for callback */ 180 host = nlmclnt_lookup_host(&rqstp->rq_addr, 181 rqstp->rq_prot, rqstp->rq_vers); 182 if (host == NULL) 183 return NULL; 184 185 /* Allocate memory for block, and initialize arguments */ 186 if (!(block = (struct nlm_block *) kmalloc(sizeof(*block), GFP_KERNEL))) 187 goto failed; 188 memset(block, 0, sizeof(*block)); 189 locks_init_lock(&block->b_call.a_args.lock.fl); 190 locks_init_lock(&block->b_call.a_res.lock.fl); 191 192 if (!nlmclnt_setgrantargs(&block->b_call, lock)) 193 goto failed_free; 194 195 /* Set notifier function for VFS, and init args */ 196 block->b_call.a_args.lock.fl.fl_lmops = &nlmsvc_lock_operations; 197 block->b_call.a_args.cookie = *cookie; /* see above */ 198 199 dprintk("lockd: created block %p...\n", block); 200 201 /* Create and initialize the block */ 202 block->b_daemon = rqstp->rq_server; 203 block->b_host = host; 204 block->b_file = file; 205 206 /* Add to file's list of blocks */ 207 block->b_fnext = file->f_blocks; 208 file->f_blocks = block; 209 210 /* Set up RPC arguments for callback */ 211 call = &block->b_call; 212 call->a_host = host; 213 call->a_flags = RPC_TASK_ASYNC; 214 215 return block; 216 217 failed_free: 218 kfree(block); 219 failed: 220 nlm_release_host(host); 221 return NULL; 222 } 223 224 /* 225 * Delete a block. If the lock was cancelled or the grant callback 226 * failed, unlock is set to 1. 227 * It is the caller's responsibility to check whether the file 228 * can be closed hereafter. 229 */ 230 static int 231 nlmsvc_delete_block(struct nlm_block *block, int unlock) 232 { 233 struct file_lock *fl = &block->b_call.a_args.lock.fl; 234 struct nlm_file *file = block->b_file; 235 struct nlm_block **bp; 236 int status = 0; 237 238 dprintk("lockd: deleting block %p...\n", block); 239 240 /* Remove block from list */ 241 nlmsvc_remove_block(block); 242 if (unlock) 243 status = posix_unblock_lock(file->f_file, fl); 244 245 /* If the block is in the middle of a GRANT callback, 246 * don't kill it yet. */ 247 if (block->b_incall) { 248 nlmsvc_insert_block(block, NLM_NEVER); 249 block->b_done = 1; 250 return status; 251 } 252 253 /* Remove block from file's list of blocks */ 254 for (bp = &file->f_blocks; *bp; bp = &(*bp)->b_fnext) { 255 if (*bp == block) { 256 *bp = block->b_fnext; 257 break; 258 } 259 } 260 261 if (block->b_host) 262 nlm_release_host(block->b_host); 263 nlmclnt_freegrantargs(&block->b_call); 264 kfree(block); 265 return status; 266 } 267 268 /* 269 * Loop over all blocks and perform the action specified. 270 * (NLM_ACT_CHECK handled by nlmsvc_inspect_file). 271 */ 272 int 273 nlmsvc_traverse_blocks(struct nlm_host *host, struct nlm_file *file, int action) 274 { 275 struct nlm_block *block, *next; 276 /* XXX: Will everything get cleaned up if we don't unlock here? */ 277 278 down(&file->f_sema); 279 for (block = file->f_blocks; block; block = next) { 280 next = block->b_fnext; 281 if (action == NLM_ACT_MARK) 282 block->b_host->h_inuse = 1; 283 else if (action == NLM_ACT_UNLOCK) { 284 if (host == NULL || host == block->b_host) 285 nlmsvc_delete_block(block, 1); 286 } 287 } 288 up(&file->f_sema); 289 return 0; 290 } 291 292 /* 293 * Attempt to establish a lock, and if it can't be granted, block it 294 * if required. 295 */ 296 u32 297 nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file, 298 struct nlm_lock *lock, int wait, struct nlm_cookie *cookie) 299 { 300 struct file_lock *conflock; 301 struct nlm_block *block; 302 int error; 303 304 dprintk("lockd: nlmsvc_lock(%s/%ld, ty=%d, pi=%d, %Ld-%Ld, bl=%d)\n", 305 file->f_file->f_dentry->d_inode->i_sb->s_id, 306 file->f_file->f_dentry->d_inode->i_ino, 307 lock->fl.fl_type, lock->fl.fl_pid, 308 (long long)lock->fl.fl_start, 309 (long long)lock->fl.fl_end, 310 wait); 311 312 313 /* Get existing block (in case client is busy-waiting) */ 314 block = nlmsvc_lookup_block(file, lock, 0); 315 316 lock->fl.fl_flags |= FL_LOCKD; 317 318 again: 319 /* Lock file against concurrent access */ 320 down(&file->f_sema); 321 322 if (!(conflock = posix_test_lock(file->f_file, &lock->fl))) { 323 error = posix_lock_file(file->f_file, &lock->fl); 324 325 if (block) 326 nlmsvc_delete_block(block, 0); 327 up(&file->f_sema); 328 329 dprintk("lockd: posix_lock_file returned %d\n", -error); 330 switch(-error) { 331 case 0: 332 return nlm_granted; 333 case EDEADLK: 334 return nlm_deadlock; 335 case EAGAIN: 336 return nlm_lck_denied; 337 default: /* includes ENOLCK */ 338 return nlm_lck_denied_nolocks; 339 } 340 } 341 342 if (!wait) { 343 up(&file->f_sema); 344 return nlm_lck_denied; 345 } 346 347 if (posix_locks_deadlock(&lock->fl, conflock)) { 348 up(&file->f_sema); 349 return nlm_deadlock; 350 } 351 352 /* If we don't have a block, create and initialize it. Then 353 * retry because we may have slept in kmalloc. */ 354 /* We have to release f_sema as nlmsvc_create_block may try to 355 * to claim it while doing host garbage collection */ 356 if (block == NULL) { 357 up(&file->f_sema); 358 dprintk("lockd: blocking on this lock (allocating).\n"); 359 if (!(block = nlmsvc_create_block(rqstp, file, lock, cookie))) 360 return nlm_lck_denied_nolocks; 361 goto again; 362 } 363 364 /* Append to list of blocked */ 365 nlmsvc_insert_block(block, NLM_NEVER); 366 367 if (list_empty(&block->b_call.a_args.lock.fl.fl_block)) { 368 /* Now add block to block list of the conflicting lock 369 if we haven't done so. */ 370 dprintk("lockd: blocking on this lock.\n"); 371 posix_block_lock(conflock, &block->b_call.a_args.lock.fl); 372 } 373 374 up(&file->f_sema); 375 return nlm_lck_blocked; 376 } 377 378 /* 379 * Test for presence of a conflicting lock. 380 */ 381 u32 382 nlmsvc_testlock(struct nlm_file *file, struct nlm_lock *lock, 383 struct nlm_lock *conflock) 384 { 385 struct file_lock *fl; 386 387 dprintk("lockd: nlmsvc_testlock(%s/%ld, ty=%d, %Ld-%Ld)\n", 388 file->f_file->f_dentry->d_inode->i_sb->s_id, 389 file->f_file->f_dentry->d_inode->i_ino, 390 lock->fl.fl_type, 391 (long long)lock->fl.fl_start, 392 (long long)lock->fl.fl_end); 393 394 if ((fl = posix_test_lock(file->f_file, &lock->fl)) != NULL) { 395 dprintk("lockd: conflicting lock(ty=%d, %Ld-%Ld)\n", 396 fl->fl_type, (long long)fl->fl_start, 397 (long long)fl->fl_end); 398 conflock->caller = "somehost"; /* FIXME */ 399 conflock->oh.len = 0; /* don't return OH info */ 400 conflock->fl = *fl; 401 return nlm_lck_denied; 402 } 403 404 return nlm_granted; 405 } 406 407 /* 408 * Remove a lock. 409 * This implies a CANCEL call: We send a GRANT_MSG, the client replies 410 * with a GRANT_RES call which gets lost, and calls UNLOCK immediately 411 * afterwards. In this case the block will still be there, and hence 412 * must be removed. 413 */ 414 u32 415 nlmsvc_unlock(struct nlm_file *file, struct nlm_lock *lock) 416 { 417 int error; 418 419 dprintk("lockd: nlmsvc_unlock(%s/%ld, pi=%d, %Ld-%Ld)\n", 420 file->f_file->f_dentry->d_inode->i_sb->s_id, 421 file->f_file->f_dentry->d_inode->i_ino, 422 lock->fl.fl_pid, 423 (long long)lock->fl.fl_start, 424 (long long)lock->fl.fl_end); 425 426 /* First, cancel any lock that might be there */ 427 nlmsvc_cancel_blocked(file, lock); 428 429 lock->fl.fl_type = F_UNLCK; 430 error = posix_lock_file(file->f_file, &lock->fl); 431 432 return (error < 0)? nlm_lck_denied_nolocks : nlm_granted; 433 } 434 435 /* 436 * Cancel a previously blocked request. 437 * 438 * A cancel request always overrides any grant that may currently 439 * be in progress. 440 * The calling procedure must check whether the file can be closed. 441 */ 442 u32 443 nlmsvc_cancel_blocked(struct nlm_file *file, struct nlm_lock *lock) 444 { 445 struct nlm_block *block; 446 int status = 0; 447 448 dprintk("lockd: nlmsvc_cancel(%s/%ld, pi=%d, %Ld-%Ld)\n", 449 file->f_file->f_dentry->d_inode->i_sb->s_id, 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 status = nlmsvc_delete_block(block, 1); 458 up(&file->f_sema); 459 return status ? nlm_lck_denied : 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 for (bp = &nlm_blocked; (block = *bp) != 0; bp = &block->b_next) { 476 if (nlm_compare_locks(&block->b_call.a_args.lock.fl, fl)) { 477 nlmsvc_insert_block(block, 0); 478 svc_wake_up(block->b_daemon); 479 return; 480 } 481 } 482 483 printk(KERN_WARNING "lockd: notification for unknown block!\n"); 484 } 485 486 static int nlmsvc_same_owner(struct file_lock *fl1, struct file_lock *fl2) 487 { 488 return fl1->fl_owner == fl2->fl_owner && fl1->fl_pid == fl2->fl_pid; 489 } 490 491 struct lock_manager_operations nlmsvc_lock_operations = { 492 .fl_compare_owner = nlmsvc_same_owner, 493 .fl_notify = nlmsvc_notify_blocked, 494 }; 495 496 /* 497 * Try to claim a lock that was previously blocked. 498 * 499 * Note that we use both the RPC_GRANTED_MSG call _and_ an async 500 * RPC thread when notifying the client. This seems like overkill... 501 * Here's why: 502 * - we don't want to use a synchronous RPC thread, otherwise 503 * we might find ourselves hanging on a dead portmapper. 504 * - Some lockd implementations (e.g. HP) don't react to 505 * RPC_GRANTED calls; they seem to insist on RPC_GRANTED_MSG calls. 506 */ 507 static void 508 nlmsvc_grant_blocked(struct nlm_block *block) 509 { 510 struct nlm_file *file = block->b_file; 511 struct nlm_lock *lock = &block->b_call.a_args.lock; 512 struct file_lock *conflock; 513 int error; 514 515 dprintk("lockd: grant blocked lock %p\n", block); 516 517 /* First thing is lock the file */ 518 down(&file->f_sema); 519 520 /* Unlink block request from list */ 521 nlmsvc_remove_block(block); 522 523 /* If b_granted is true this means we've been here before. 524 * Just retry the grant callback, possibly refreshing the RPC 525 * binding */ 526 if (block->b_granted) { 527 nlm_rebind_host(block->b_host); 528 goto callback; 529 } 530 531 /* Try the lock operation again */ 532 if ((conflock = posix_test_lock(file->f_file, &lock->fl)) != NULL) { 533 /* Bummer, we blocked again */ 534 dprintk("lockd: lock still blocked\n"); 535 nlmsvc_insert_block(block, NLM_NEVER); 536 posix_block_lock(conflock, &lock->fl); 537 up(&file->f_sema); 538 return; 539 } 540 541 /* Alright, no conflicting lock. Now lock it for real. If the 542 * following yields an error, this is most probably due to low 543 * memory. Retry the lock in a few seconds. 544 */ 545 if ((error = posix_lock_file(file->f_file, &lock->fl)) < 0) { 546 printk(KERN_WARNING "lockd: unexpected error %d in %s!\n", 547 -error, __FUNCTION__); 548 nlmsvc_insert_block(block, 10 * HZ); 549 up(&file->f_sema); 550 return; 551 } 552 553 callback: 554 /* Lock was granted by VFS. */ 555 dprintk("lockd: GRANTing blocked lock.\n"); 556 block->b_granted = 1; 557 block->b_incall = 1; 558 559 /* Schedule next grant callback in 30 seconds */ 560 nlmsvc_insert_block(block, 30 * HZ); 561 562 /* Call the client */ 563 nlm_get_host(block->b_call.a_host); 564 if (nlmsvc_async_call(&block->b_call, NLMPROC_GRANTED_MSG, 565 &nlmsvc_grant_ops) < 0) 566 nlm_release_host(block->b_call.a_host); 567 up(&file->f_sema); 568 } 569 570 /* 571 * This is the callback from the RPC layer when the NLM_GRANTED_MSG 572 * RPC call has succeeded or timed out. 573 * Like all RPC callbacks, it is invoked by the rpciod process, so it 574 * better not sleep. Therefore, we put the blocked lock on the nlm_blocked 575 * chain once more in order to have it removed by lockd itself (which can 576 * then sleep on the file semaphore without disrupting e.g. the nfs client). 577 */ 578 static void nlmsvc_grant_callback(struct rpc_task *task, void *data) 579 { 580 struct nlm_rqst *call = data; 581 struct nlm_block *block; 582 unsigned long timeout; 583 struct sockaddr_in *peer_addr = RPC_PEERADDR(task->tk_client); 584 585 dprintk("lockd: GRANT_MSG RPC callback\n"); 586 dprintk("callback: looking for cookie %s, host (%u.%u.%u.%u)\n", 587 nlmdbg_cookie2a(&call->a_args.cookie), 588 NIPQUAD(peer_addr->sin_addr.s_addr)); 589 if (!(block = nlmsvc_find_block(&call->a_args.cookie, peer_addr))) { 590 dprintk("lockd: no block for cookie %s, host (%u.%u.%u.%u)\n", 591 nlmdbg_cookie2a(&call->a_args.cookie), 592 NIPQUAD(peer_addr->sin_addr.s_addr)); 593 return; 594 } 595 596 /* Technically, we should down the file semaphore here. Since we 597 * move the block towards the head of the queue only, no harm 598 * can be done, though. */ 599 if (task->tk_status < 0) { 600 /* RPC error: Re-insert for retransmission */ 601 timeout = 10 * HZ; 602 } else if (block->b_done) { 603 /* Block already removed, kill it for real */ 604 timeout = 0; 605 } else { 606 /* Call was successful, now wait for client callback */ 607 timeout = 60 * HZ; 608 } 609 nlmsvc_insert_block(block, timeout); 610 svc_wake_up(block->b_daemon); 611 block->b_incall = 0; 612 613 nlm_release_host(call->a_host); 614 } 615 616 static const struct rpc_call_ops nlmsvc_grant_ops = { 617 .rpc_call_done = nlmsvc_grant_callback, 618 }; 619 620 /* 621 * We received a GRANT_RES callback. Try to find the corresponding 622 * block. 623 */ 624 void 625 nlmsvc_grant_reply(struct svc_rqst *rqstp, struct nlm_cookie *cookie, u32 status) 626 { 627 struct nlm_block *block; 628 struct nlm_file *file; 629 630 dprintk("grant_reply: looking for cookie %x, host (%08x), s=%d \n", 631 *(unsigned int *)(cookie->data), 632 ntohl(rqstp->rq_addr.sin_addr.s_addr), status); 633 if (!(block = nlmsvc_find_block(cookie, &rqstp->rq_addr))) 634 return; 635 file = block->b_file; 636 637 file->f_count++; 638 down(&file->f_sema); 639 block = nlmsvc_find_block(cookie, &rqstp->rq_addr); 640 if (block) { 641 if (status == NLM_LCK_DENIED_GRACE_PERIOD) { 642 /* Try again in a couple of seconds */ 643 nlmsvc_insert_block(block, 10 * HZ); 644 up(&file->f_sema); 645 } else { 646 /* Lock is now held by client, or has been rejected. 647 * In both cases, the block should be removed. */ 648 up(&file->f_sema); 649 if (status == NLM_LCK_GRANTED) 650 nlmsvc_delete_block(block, 0); 651 else 652 nlmsvc_delete_block(block, 1); 653 } 654 } 655 nlm_release_file(file); 656 } 657 658 /* 659 * Retry all blocked locks that have been notified. This is where lockd 660 * picks up locks that can be granted, or grant notifications that must 661 * be retransmitted. 662 */ 663 unsigned long 664 nlmsvc_retry_blocked(void) 665 { 666 struct nlm_block *block; 667 668 dprintk("nlmsvc_retry_blocked(%p, when=%ld)\n", 669 nlm_blocked, 670 nlm_blocked? nlm_blocked->b_when : 0); 671 while ((block = nlm_blocked) != 0) { 672 if (block->b_when == NLM_NEVER) 673 break; 674 if (time_after(block->b_when,jiffies)) 675 break; 676 dprintk("nlmsvc_retry_blocked(%p, when=%ld, done=%d)\n", 677 block, block->b_when, block->b_done); 678 if (block->b_done) 679 nlmsvc_delete_block(block, 0); 680 else 681 nlmsvc_grant_blocked(block); 682 } 683 684 if ((block = nlm_blocked) && block->b_when != NLM_NEVER) 685 return (block->b_when - jiffies); 686 687 return MAX_SCHEDULE_TIMEOUT; 688 } 689