1 /* 2 * fs/fs-writeback.c 3 * 4 * Copyright (C) 2002, Linus Torvalds. 5 * 6 * Contains all the functions related to writing back and waiting 7 * upon dirty inodes against superblocks, and writing back dirty 8 * pages against inodes. ie: data writeback. Writeout of the 9 * inode itself is not handled here. 10 * 11 * 10Apr2002 akpm@zip.com.au 12 * Split out of fs/inode.c 13 * Additions for address_space-based writeback 14 */ 15 16 #include <linux/kernel.h> 17 #include <linux/spinlock.h> 18 #include <linux/sched.h> 19 #include <linux/fs.h> 20 #include <linux/mm.h> 21 #include <linux/writeback.h> 22 #include <linux/blkdev.h> 23 #include <linux/backing-dev.h> 24 #include <linux/buffer_head.h> 25 #include "internal.h" 26 27 /** 28 * __mark_inode_dirty - internal function 29 * @inode: inode to mark 30 * @flags: what kind of dirty (i.e. I_DIRTY_SYNC) 31 * Mark an inode as dirty. Callers should use mark_inode_dirty or 32 * mark_inode_dirty_sync. 33 * 34 * Put the inode on the super block's dirty list. 35 * 36 * CAREFUL! We mark it dirty unconditionally, but move it onto the 37 * dirty list only if it is hashed or if it refers to a blockdev. 38 * If it was not hashed, it will never be added to the dirty list 39 * even if it is later hashed, as it will have been marked dirty already. 40 * 41 * In short, make sure you hash any inodes _before_ you start marking 42 * them dirty. 43 * 44 * This function *must* be atomic for the I_DIRTY_PAGES case - 45 * set_page_dirty() is called under spinlock in several places. 46 * 47 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of 48 * the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of 49 * the kernel-internal blockdev inode represents the dirtying time of the 50 * blockdev's pages. This is why for I_DIRTY_PAGES we always use 51 * page->mapping->host, so the page-dirtying time is recorded in the internal 52 * blockdev inode. 53 */ 54 void __mark_inode_dirty(struct inode *inode, int flags) 55 { 56 struct super_block *sb = inode->i_sb; 57 58 /* 59 * Don't do this for I_DIRTY_PAGES - that doesn't actually 60 * dirty the inode itself 61 */ 62 if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) { 63 if (sb->s_op->dirty_inode) 64 sb->s_op->dirty_inode(inode); 65 } 66 67 /* 68 * make sure that changes are seen by all cpus before we test i_state 69 * -- mikulas 70 */ 71 smp_mb(); 72 73 /* avoid the locking if we can */ 74 if ((inode->i_state & flags) == flags) 75 return; 76 77 if (unlikely(block_dump)) { 78 struct dentry *dentry = NULL; 79 const char *name = "?"; 80 81 if (!list_empty(&inode->i_dentry)) { 82 dentry = list_entry(inode->i_dentry.next, 83 struct dentry, d_alias); 84 if (dentry && dentry->d_name.name) 85 name = (const char *) dentry->d_name.name; 86 } 87 88 if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) 89 printk(KERN_DEBUG 90 "%s(%d): dirtied inode %lu (%s) on %s\n", 91 current->comm, current->pid, inode->i_ino, 92 name, inode->i_sb->s_id); 93 } 94 95 spin_lock(&inode_lock); 96 if ((inode->i_state & flags) != flags) { 97 const int was_dirty = inode->i_state & I_DIRTY; 98 99 inode->i_state |= flags; 100 101 /* 102 * If the inode is locked, just update its dirty state. 103 * The unlocker will place the inode on the appropriate 104 * superblock list, based upon its state. 105 */ 106 if (inode->i_state & I_LOCK) 107 goto out; 108 109 /* 110 * Only add valid (hashed) inodes to the superblock's 111 * dirty list. Add blockdev inodes as well. 112 */ 113 if (!S_ISBLK(inode->i_mode)) { 114 if (hlist_unhashed(&inode->i_hash)) 115 goto out; 116 } 117 if (inode->i_state & (I_FREEING|I_CLEAR)) 118 goto out; 119 120 /* 121 * If the inode was already on s_dirty or s_io, don't 122 * reposition it (that would break s_dirty time-ordering). 123 */ 124 if (!was_dirty) { 125 inode->dirtied_when = jiffies; 126 list_move(&inode->i_list, &sb->s_dirty); 127 } 128 } 129 out: 130 spin_unlock(&inode_lock); 131 } 132 133 EXPORT_SYMBOL(__mark_inode_dirty); 134 135 static int write_inode(struct inode *inode, int sync) 136 { 137 if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) 138 return inode->i_sb->s_op->write_inode(inode, sync); 139 return 0; 140 } 141 142 /* 143 * Write a single inode's dirty pages and inode data out to disk. 144 * If `wait' is set, wait on the writeout. 145 * 146 * The whole writeout design is quite complex and fragile. We want to avoid 147 * starvation of particular inodes when others are being redirtied, prevent 148 * livelocks, etc. 149 * 150 * Called under inode_lock. 151 */ 152 static int 153 __sync_single_inode(struct inode *inode, struct writeback_control *wbc) 154 { 155 unsigned dirty; 156 struct address_space *mapping = inode->i_mapping; 157 struct super_block *sb = inode->i_sb; 158 int wait = wbc->sync_mode == WB_SYNC_ALL; 159 int ret; 160 161 BUG_ON(inode->i_state & I_LOCK); 162 163 /* Set I_LOCK, reset I_DIRTY */ 164 dirty = inode->i_state & I_DIRTY; 165 inode->i_state |= I_LOCK; 166 inode->i_state &= ~I_DIRTY; 167 168 spin_unlock(&inode_lock); 169 170 ret = do_writepages(mapping, wbc); 171 172 /* Don't write the inode if only I_DIRTY_PAGES was set */ 173 if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) { 174 int err = write_inode(inode, wait); 175 if (ret == 0) 176 ret = err; 177 } 178 179 if (wait) { 180 int err = filemap_fdatawait(mapping); 181 if (ret == 0) 182 ret = err; 183 } 184 185 spin_lock(&inode_lock); 186 inode->i_state &= ~I_LOCK; 187 if (!(inode->i_state & I_FREEING)) { 188 if (!(inode->i_state & I_DIRTY) && 189 mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) { 190 /* 191 * We didn't write back all the pages. nfs_writepages() 192 * sometimes bales out without doing anything. Redirty 193 * the inode. It is still on sb->s_io. 194 */ 195 if (wbc->for_kupdate) { 196 /* 197 * For the kupdate function we leave the inode 198 * at the head of sb_dirty so it will get more 199 * writeout as soon as the queue becomes 200 * uncongested. 201 */ 202 inode->i_state |= I_DIRTY_PAGES; 203 list_move_tail(&inode->i_list, &sb->s_dirty); 204 } else { 205 /* 206 * Otherwise fully redirty the inode so that 207 * other inodes on this superblock will get some 208 * writeout. Otherwise heavy writing to one 209 * file would indefinitely suspend writeout of 210 * all the other files. 211 */ 212 inode->i_state |= I_DIRTY_PAGES; 213 inode->dirtied_when = jiffies; 214 list_move(&inode->i_list, &sb->s_dirty); 215 } 216 } else if (inode->i_state & I_DIRTY) { 217 /* 218 * Someone redirtied the inode while were writing back 219 * the pages. 220 */ 221 list_move(&inode->i_list, &sb->s_dirty); 222 } else if (atomic_read(&inode->i_count)) { 223 /* 224 * The inode is clean, inuse 225 */ 226 list_move(&inode->i_list, &inode_in_use); 227 } else { 228 /* 229 * The inode is clean, unused 230 */ 231 list_move(&inode->i_list, &inode_unused); 232 } 233 } 234 wake_up_inode(inode); 235 return ret; 236 } 237 238 /* 239 * Write out an inode's dirty pages. Called under inode_lock. Either the 240 * caller has ref on the inode (either via __iget or via syscall against an fd) 241 * or the inode has I_WILL_FREE set (via generic_forget_inode) 242 */ 243 static int 244 __writeback_single_inode(struct inode *inode, struct writeback_control *wbc) 245 { 246 wait_queue_head_t *wqh; 247 248 if (!atomic_read(&inode->i_count)) 249 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING))); 250 else 251 WARN_ON(inode->i_state & I_WILL_FREE); 252 253 if ((wbc->sync_mode != WB_SYNC_ALL) && (inode->i_state & I_LOCK)) { 254 struct address_space *mapping = inode->i_mapping; 255 int ret; 256 257 list_move(&inode->i_list, &inode->i_sb->s_dirty); 258 259 /* 260 * Even if we don't actually write the inode itself here, 261 * we can at least start some of the data writeout.. 262 */ 263 spin_unlock(&inode_lock); 264 ret = do_writepages(mapping, wbc); 265 spin_lock(&inode_lock); 266 return ret; 267 } 268 269 /* 270 * It's a data-integrity sync. We must wait. 271 */ 272 if (inode->i_state & I_LOCK) { 273 DEFINE_WAIT_BIT(wq, &inode->i_state, __I_LOCK); 274 275 wqh = bit_waitqueue(&inode->i_state, __I_LOCK); 276 do { 277 spin_unlock(&inode_lock); 278 __wait_on_bit(wqh, &wq, inode_wait, 279 TASK_UNINTERRUPTIBLE); 280 spin_lock(&inode_lock); 281 } while (inode->i_state & I_LOCK); 282 } 283 return __sync_single_inode(inode, wbc); 284 } 285 286 /* 287 * Write out a superblock's list of dirty inodes. A wait will be performed 288 * upon no inodes, all inodes or the final one, depending upon sync_mode. 289 * 290 * If older_than_this is non-NULL, then only write out inodes which 291 * had their first dirtying at a time earlier than *older_than_this. 292 * 293 * If we're a pdlfush thread, then implement pdflush collision avoidance 294 * against the entire list. 295 * 296 * WB_SYNC_HOLD is a hack for sys_sync(): reattach the inode to sb->s_dirty so 297 * that it can be located for waiting on in __writeback_single_inode(). 298 * 299 * Called under inode_lock. 300 * 301 * If `bdi' is non-zero then we're being asked to writeback a specific queue. 302 * This function assumes that the blockdev superblock's inodes are backed by 303 * a variety of queues, so all inodes are searched. For other superblocks, 304 * assume that all inodes are backed by the same queue. 305 * 306 * FIXME: this linear search could get expensive with many fileystems. But 307 * how to fix? We need to go from an address_space to all inodes which share 308 * a queue with that address_space. (Easy: have a global "dirty superblocks" 309 * list). 310 * 311 * The inodes to be written are parked on sb->s_io. They are moved back onto 312 * sb->s_dirty as they are selected for writing. This way, none can be missed 313 * on the writer throttling path, and we get decent balancing between many 314 * throttled threads: we don't want them all piling up on __wait_on_inode. 315 */ 316 static void 317 sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc) 318 { 319 const unsigned long start = jiffies; /* livelock avoidance */ 320 321 if (!wbc->for_kupdate || list_empty(&sb->s_io)) 322 list_splice_init(&sb->s_dirty, &sb->s_io); 323 324 while (!list_empty(&sb->s_io)) { 325 struct inode *inode = list_entry(sb->s_io.prev, 326 struct inode, i_list); 327 struct address_space *mapping = inode->i_mapping; 328 struct backing_dev_info *bdi = mapping->backing_dev_info; 329 long pages_skipped; 330 331 if (!bdi_cap_writeback_dirty(bdi)) { 332 list_move(&inode->i_list, &sb->s_dirty); 333 if (sb_is_blkdev_sb(sb)) { 334 /* 335 * Dirty memory-backed blockdev: the ramdisk 336 * driver does this. Skip just this inode 337 */ 338 continue; 339 } 340 /* 341 * Dirty memory-backed inode against a filesystem other 342 * than the kernel-internal bdev filesystem. Skip the 343 * entire superblock. 344 */ 345 break; 346 } 347 348 if (wbc->nonblocking && bdi_write_congested(bdi)) { 349 wbc->encountered_congestion = 1; 350 if (!sb_is_blkdev_sb(sb)) 351 break; /* Skip a congested fs */ 352 list_move(&inode->i_list, &sb->s_dirty); 353 continue; /* Skip a congested blockdev */ 354 } 355 356 if (wbc->bdi && bdi != wbc->bdi) { 357 if (!sb_is_blkdev_sb(sb)) 358 break; /* fs has the wrong queue */ 359 list_move(&inode->i_list, &sb->s_dirty); 360 continue; /* blockdev has wrong queue */ 361 } 362 363 /* Was this inode dirtied after sync_sb_inodes was called? */ 364 if (time_after(inode->dirtied_when, start)) 365 break; 366 367 /* Was this inode dirtied too recently? */ 368 if (wbc->older_than_this && time_after(inode->dirtied_when, 369 *wbc->older_than_this)) 370 break; 371 372 /* Is another pdflush already flushing this queue? */ 373 if (current_is_pdflush() && !writeback_acquire(bdi)) 374 break; 375 376 BUG_ON(inode->i_state & I_FREEING); 377 __iget(inode); 378 pages_skipped = wbc->pages_skipped; 379 __writeback_single_inode(inode, wbc); 380 if (wbc->sync_mode == WB_SYNC_HOLD) { 381 inode->dirtied_when = jiffies; 382 list_move(&inode->i_list, &sb->s_dirty); 383 } 384 if (current_is_pdflush()) 385 writeback_release(bdi); 386 if (wbc->pages_skipped != pages_skipped) { 387 /* 388 * writeback is not making progress due to locked 389 * buffers. Skip this inode for now. 390 */ 391 list_move(&inode->i_list, &sb->s_dirty); 392 } 393 spin_unlock(&inode_lock); 394 iput(inode); 395 cond_resched(); 396 spin_lock(&inode_lock); 397 if (wbc->nr_to_write <= 0) 398 break; 399 } 400 return; /* Leave any unwritten inodes on s_io */ 401 } 402 403 /* 404 * Start writeback of dirty pagecache data against all unlocked inodes. 405 * 406 * Note: 407 * We don't need to grab a reference to superblock here. If it has non-empty 408 * ->s_dirty it's hadn't been killed yet and kill_super() won't proceed 409 * past sync_inodes_sb() until both the ->s_dirty and ->s_io lists are 410 * empty. Since __sync_single_inode() regains inode_lock before it finally moves 411 * inode from superblock lists we are OK. 412 * 413 * If `older_than_this' is non-zero then only flush inodes which have a 414 * flushtime older than *older_than_this. 415 * 416 * If `bdi' is non-zero then we will scan the first inode against each 417 * superblock until we find the matching ones. One group will be the dirty 418 * inodes against a filesystem. Then when we hit the dummy blockdev superblock, 419 * sync_sb_inodes will seekout the blockdev which matches `bdi'. Maybe not 420 * super-efficient but we're about to do a ton of I/O... 421 */ 422 void 423 writeback_inodes(struct writeback_control *wbc) 424 { 425 struct super_block *sb; 426 427 might_sleep(); 428 spin_lock(&sb_lock); 429 restart: 430 sb = sb_entry(super_blocks.prev); 431 for (; sb != sb_entry(&super_blocks); sb = sb_entry(sb->s_list.prev)) { 432 if (!list_empty(&sb->s_dirty) || !list_empty(&sb->s_io)) { 433 /* we're making our own get_super here */ 434 sb->s_count++; 435 spin_unlock(&sb_lock); 436 /* 437 * If we can't get the readlock, there's no sense in 438 * waiting around, most of the time the FS is going to 439 * be unmounted by the time it is released. 440 */ 441 if (down_read_trylock(&sb->s_umount)) { 442 if (sb->s_root) { 443 spin_lock(&inode_lock); 444 sync_sb_inodes(sb, wbc); 445 spin_unlock(&inode_lock); 446 } 447 up_read(&sb->s_umount); 448 } 449 spin_lock(&sb_lock); 450 if (__put_super_and_need_restart(sb)) 451 goto restart; 452 } 453 if (wbc->nr_to_write <= 0) 454 break; 455 } 456 spin_unlock(&sb_lock); 457 } 458 459 /* 460 * writeback and wait upon the filesystem's dirty inodes. The caller will 461 * do this in two passes - one to write, and one to wait. WB_SYNC_HOLD is 462 * used to park the written inodes on sb->s_dirty for the wait pass. 463 * 464 * A finite limit is set on the number of pages which will be written. 465 * To prevent infinite livelock of sys_sync(). 466 * 467 * We add in the number of potentially dirty inodes, because each inode write 468 * can dirty pagecache in the underlying blockdev. 469 */ 470 void sync_inodes_sb(struct super_block *sb, int wait) 471 { 472 struct writeback_control wbc = { 473 .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_HOLD, 474 .range_start = 0, 475 .range_end = LLONG_MAX, 476 }; 477 unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY); 478 unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS); 479 480 wbc.nr_to_write = nr_dirty + nr_unstable + 481 (inodes_stat.nr_inodes - inodes_stat.nr_unused) + 482 nr_dirty + nr_unstable; 483 wbc.nr_to_write += wbc.nr_to_write / 2; /* Bit more for luck */ 484 spin_lock(&inode_lock); 485 sync_sb_inodes(sb, &wbc); 486 spin_unlock(&inode_lock); 487 } 488 489 /* 490 * Rather lame livelock avoidance. 491 */ 492 static void set_sb_syncing(int val) 493 { 494 struct super_block *sb; 495 spin_lock(&sb_lock); 496 sb = sb_entry(super_blocks.prev); 497 for (; sb != sb_entry(&super_blocks); sb = sb_entry(sb->s_list.prev)) { 498 sb->s_syncing = val; 499 } 500 spin_unlock(&sb_lock); 501 } 502 503 /** 504 * sync_inodes - writes all inodes to disk 505 * @wait: wait for completion 506 * 507 * sync_inodes() goes through each super block's dirty inode list, writes the 508 * inodes out, waits on the writeout and puts the inodes back on the normal 509 * list. 510 * 511 * This is for sys_sync(). fsync_dev() uses the same algorithm. The subtle 512 * part of the sync functions is that the blockdev "superblock" is processed 513 * last. This is because the write_inode() function of a typical fs will 514 * perform no I/O, but will mark buffers in the blockdev mapping as dirty. 515 * What we want to do is to perform all that dirtying first, and then write 516 * back all those inode blocks via the blockdev mapping in one sweep. So the 517 * additional (somewhat redundant) sync_blockdev() calls here are to make 518 * sure that really happens. Because if we call sync_inodes_sb(wait=1) with 519 * outstanding dirty inodes, the writeback goes block-at-a-time within the 520 * filesystem's write_inode(). This is extremely slow. 521 */ 522 static void __sync_inodes(int wait) 523 { 524 struct super_block *sb; 525 526 spin_lock(&sb_lock); 527 restart: 528 list_for_each_entry(sb, &super_blocks, s_list) { 529 if (sb->s_syncing) 530 continue; 531 sb->s_syncing = 1; 532 sb->s_count++; 533 spin_unlock(&sb_lock); 534 down_read(&sb->s_umount); 535 if (sb->s_root) { 536 sync_inodes_sb(sb, wait); 537 sync_blockdev(sb->s_bdev); 538 } 539 up_read(&sb->s_umount); 540 spin_lock(&sb_lock); 541 if (__put_super_and_need_restart(sb)) 542 goto restart; 543 } 544 spin_unlock(&sb_lock); 545 } 546 547 void sync_inodes(int wait) 548 { 549 set_sb_syncing(0); 550 __sync_inodes(0); 551 552 if (wait) { 553 set_sb_syncing(0); 554 __sync_inodes(1); 555 } 556 } 557 558 /** 559 * write_inode_now - write an inode to disk 560 * @inode: inode to write to disk 561 * @sync: whether the write should be synchronous or not 562 * 563 * This function commits an inode to disk immediately if it is dirty. This is 564 * primarily needed by knfsd. 565 * 566 * The caller must either have a ref on the inode or must have set I_WILL_FREE. 567 */ 568 int write_inode_now(struct inode *inode, int sync) 569 { 570 int ret; 571 struct writeback_control wbc = { 572 .nr_to_write = LONG_MAX, 573 .sync_mode = WB_SYNC_ALL, 574 .range_start = 0, 575 .range_end = LLONG_MAX, 576 }; 577 578 if (!mapping_cap_writeback_dirty(inode->i_mapping)) 579 wbc.nr_to_write = 0; 580 581 might_sleep(); 582 spin_lock(&inode_lock); 583 ret = __writeback_single_inode(inode, &wbc); 584 spin_unlock(&inode_lock); 585 if (sync) 586 wait_on_inode(inode); 587 return ret; 588 } 589 EXPORT_SYMBOL(write_inode_now); 590 591 /** 592 * sync_inode - write an inode and its pages to disk. 593 * @inode: the inode to sync 594 * @wbc: controls the writeback mode 595 * 596 * sync_inode() will write an inode and its pages to disk. It will also 597 * correctly update the inode on its superblock's dirty inode lists and will 598 * update inode->i_state. 599 * 600 * The caller must have a ref on the inode. 601 */ 602 int sync_inode(struct inode *inode, struct writeback_control *wbc) 603 { 604 int ret; 605 606 spin_lock(&inode_lock); 607 ret = __writeback_single_inode(inode, wbc); 608 spin_unlock(&inode_lock); 609 return ret; 610 } 611 EXPORT_SYMBOL(sync_inode); 612 613 /** 614 * generic_osync_inode - flush all dirty data for a given inode to disk 615 * @inode: inode to write 616 * @mapping: the address_space that should be flushed 617 * @what: what to write and wait upon 618 * 619 * This can be called by file_write functions for files which have the 620 * O_SYNC flag set, to flush dirty writes to disk. 621 * 622 * @what is a bitmask, specifying which part of the inode's data should be 623 * written and waited upon. 624 * 625 * OSYNC_DATA: i_mapping's dirty data 626 * OSYNC_METADATA: the buffers at i_mapping->private_list 627 * OSYNC_INODE: the inode itself 628 */ 629 630 int generic_osync_inode(struct inode *inode, struct address_space *mapping, int what) 631 { 632 int err = 0; 633 int need_write_inode_now = 0; 634 int err2; 635 636 if (what & OSYNC_DATA) 637 err = filemap_fdatawrite(mapping); 638 if (what & (OSYNC_METADATA|OSYNC_DATA)) { 639 err2 = sync_mapping_buffers(mapping); 640 if (!err) 641 err = err2; 642 } 643 if (what & OSYNC_DATA) { 644 err2 = filemap_fdatawait(mapping); 645 if (!err) 646 err = err2; 647 } 648 649 spin_lock(&inode_lock); 650 if ((inode->i_state & I_DIRTY) && 651 ((what & OSYNC_INODE) || (inode->i_state & I_DIRTY_DATASYNC))) 652 need_write_inode_now = 1; 653 spin_unlock(&inode_lock); 654 655 if (need_write_inode_now) { 656 err2 = write_inode_now(inode, 1); 657 if (!err) 658 err = err2; 659 } 660 else 661 wait_on_inode(inode); 662 663 return err; 664 } 665 666 EXPORT_SYMBOL(generic_osync_inode); 667 668 /** 669 * writeback_acquire: attempt to get exclusive writeback access to a device 670 * @bdi: the device's backing_dev_info structure 671 * 672 * It is a waste of resources to have more than one pdflush thread blocked on 673 * a single request queue. Exclusion at the request_queue level is obtained 674 * via a flag in the request_queue's backing_dev_info.state. 675 * 676 * Non-request_queue-backed address_spaces will share default_backing_dev_info, 677 * unless they implement their own. Which is somewhat inefficient, as this 678 * may prevent concurrent writeback against multiple devices. 679 */ 680 int writeback_acquire(struct backing_dev_info *bdi) 681 { 682 return !test_and_set_bit(BDI_pdflush, &bdi->state); 683 } 684 685 /** 686 * writeback_in_progress: determine whether there is writeback in progress 687 * @bdi: the device's backing_dev_info structure. 688 * 689 * Determine whether there is writeback in progress against a backing device. 690 */ 691 int writeback_in_progress(struct backing_dev_info *bdi) 692 { 693 return test_bit(BDI_pdflush, &bdi->state); 694 } 695 696 /** 697 * writeback_release: relinquish exclusive writeback access against a device. 698 * @bdi: the device's backing_dev_info structure 699 */ 700 void writeback_release(struct backing_dev_info *bdi) 701 { 702 BUG_ON(!writeback_in_progress(bdi)); 703 clear_bit(BDI_pdflush, &bdi->state); 704 } 705