fs/afs/write.c

   1 /* handling of writes to regular files and writing back to the server
   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 #include <linux/backing-dev.h>
  12 #include <linux/slab.h>
  13 #include <linux/fs.h>
  14 #include <linux/pagemap.h>
  15 #include <linux/writeback.h>
  16 #include <linux/pagevec.h>
  17 #include "internal.h"
  18
  19 static int afs_write_back_from_locked_page(struct afs_writeback *wb,
  20                                            struct page *page);
  21
  22 /*
  23  * mark a page as having been made dirty and thus needing writeback
  24  */
  25 int afs_set_page_dirty(struct page *page)
  26 {
  27         _enter("");
  28         return __set_page_dirty_nobuffers(page);
  29 }
  30
  31 /*
  32  * unlink a writeback record because its usage has reached zero
  33  * - must be called with the wb->vnode->writeback_lock held
  34  */
  35 static void afs_unlink_writeback(struct afs_writeback *wb)
  36 {
  37         struct afs_writeback *front;
  38         struct afs_vnode *vnode = wb->vnode;
  39
  40         list_del_init(&wb->link);
  41         if (!list_empty(&vnode->writebacks)) {
  42                 /* if an fsync rises to the front of the queue then wake it
  43                  * up */
  44                 front = list_entry(vnode->writebacks.next,
  45                                    struct afs_writeback, link);
  46                 if (front->state == AFS_WBACK_SYNCING) {
  47                         _debug("wake up sync");
  48                         front->state = AFS_WBACK_COMPLETE;
  49                         wake_up(&front->waitq);
  50                 }
  51         }
  52 }
  53
  54 /*
  55  * free a writeback record
  56  */
  57 static void afs_free_writeback(struct afs_writeback *wb)
  58 {
  59         _enter("");
  60         key_put(wb->key);
  61         kfree(wb);
  62 }
  63
  64 /*
  65  * dispose of a reference to a writeback record
  66  */
  67 void afs_put_writeback(struct afs_writeback *wb)
  68 {
  69         struct afs_vnode *vnode = wb->vnode;
  70
  71         _enter("{%d}", wb->usage);
  72
  73         spin_lock(&vnode->writeback_lock);
  74         if (--wb->usage == 0)
  75                 afs_unlink_writeback(wb);
  76         else
  77                 wb = NULL;
  78         spin_unlock(&vnode->writeback_lock);
  79         if (wb)
  80                 afs_free_writeback(wb);
  81 }
  82
  83 /*
  84  * partly or wholly fill a page that's under preparation for writing
  85  */
  86 static int afs_fill_page(struct afs_vnode *vnode, struct key *key,
  87                          loff_t pos, struct page *page)
  88 {
  89         struct afs_read *req;
  90         loff_t i_size;
  91         int ret;
  92
  93         _enter(",,%llu", (unsigned long long)pos);
  94
  95         req = kzalloc(sizeof(struct afs_read) + sizeof(struct page *),
  96                       GFP_KERNEL);
  97         if (!req)
  98                 return -ENOMEM;
  99
 100         atomic_set(&req->usage, 1);
 101         req->pos = pos;
 102         req->nr_pages = 1;
 103         req->pages[0] = page;
 104
 105         i_size = i_size_read(&vnode->vfs_inode);
 106         if (pos + PAGE_SIZE > i_size)
 107                 req->len = i_size - pos;
 108         else
 109                 req->len = PAGE_SIZE;
 110
 111         ret = afs_vnode_fetch_data(vnode, key, req);
 112         afs_put_read(req);
 113         if (ret < 0) {
 114                 if (ret == -ENOENT) {
 115                         _debug("got NOENT from server"
 116                                " - marking file deleted and stale");
 117                         set_bit(AFS_VNODE_DELETED, &vnode->flags);
 118                         ret = -ESTALE;
 119                 }
 120         }
 121
 122         _leave(" = %d", ret);
 123         return ret;
 124 }
 125
 126 /*
 127  * prepare to perform part of a write to a page
 128  */
 129 int afs_write_begin(struct file *file, struct address_space *mapping,
 130                     loff_t pos, unsigned len, unsigned flags,
 131                     struct page **pagep, void **fsdata)
 132 {
 133         struct afs_writeback *candidate, *wb;
 134         struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
 135         struct page *page;
 136         struct key *key = file->private_data;
 137         unsigned from = pos & (PAGE_SIZE - 1);
 138         unsigned to = from + len;
 139         pgoff_t index = pos >> PAGE_SHIFT;
 140         int ret;
 141
 142         _enter("{%x:%u},{%lx},%u,%u",
 143                vnode->fid.vid, vnode->fid.vnode, index, from, to);
 144
 145         candidate = kzalloc(sizeof(*candidate), GFP_KERNEL);
 146         if (!candidate)
 147                 return -ENOMEM;
 148         candidate->vnode = vnode;
 149         candidate->first = candidate->last = index;
 150         candidate->offset_first = from;
 151         candidate->to_last = to;
 152         INIT_LIST_HEAD(&candidate->link);
 153         candidate->usage = 1;
 154         candidate->state = AFS_WBACK_PENDING;
 155         init_waitqueue_head(&candidate->waitq);
 156
 157         page = grab_cache_page_write_begin(mapping, index, flags);
 158         if (!page) {
 159                 kfree(candidate);
 160                 return -ENOMEM;
 161         }
 162         *pagep = page;
 163         /* page won't leak in error case: it eventually gets cleaned off LRU */
 164
 165         if (!PageUptodate(page) && len != PAGE_SIZE) {
 166                 ret = afs_fill_page(vnode, key, index << PAGE_SHIFT, page);
 167                 if (ret < 0) {
 168                         kfree(candidate);
 169                         _leave(" = %d [prep]", ret);
 170                         return ret;
 171                 }
 172                 SetPageUptodate(page);
 173         }
 174
 175 try_again:
 176         spin_lock(&vnode->writeback_lock);
 177
 178         /* see if this page is already pending a writeback under a suitable key
 179          * - if so we can just join onto that one */
 180         wb = (struct afs_writeback *) page_private(page);
 181         if (wb) {
 182                 if (wb->key == key && wb->state == AFS_WBACK_PENDING)
 183                         goto subsume_in_current_wb;
 184                 goto flush_conflicting_wb;
 185         }
 186
 187         if (index > 0) {
 188                 /* see if we can find an already pending writeback that we can
 189                  * append this page to */
 190                 list_for_each_entry(wb, &vnode->writebacks, link) {
 191                         if (wb->last == index - 1 && wb->key == key &&
 192                             wb->state == AFS_WBACK_PENDING)
 193                                 goto append_to_previous_wb;
 194                 }
 195         }
 196
 197         list_add_tail(&candidate->link, &vnode->writebacks);
 198         candidate->key = key_get(key);
 199         spin_unlock(&vnode->writeback_lock);
 200         SetPagePrivate(page);
 201         set_page_private(page, (unsigned long) candidate);
 202         _leave(" = 0 [new]");
 203         return 0;
 204
 205 subsume_in_current_wb:
 206         _debug("subsume");
 207         ASSERTRANGE(wb->first, <=, index, <=, wb->last);
 208         if (index == wb->first && from < wb->offset_first)
 209                 wb->offset_first = from;
 210         if (index == wb->last && to > wb->to_last)
 211                 wb->to_last = to;
 212         spin_unlock(&vnode->writeback_lock);
 213         kfree(candidate);
 214         _leave(" = 0 [sub]");
 215         return 0;
 216
 217 append_to_previous_wb:
 218         _debug("append into %lx-%lx", wb->first, wb->last);
 219         wb->usage++;
 220         wb->last++;
 221         wb->to_last = to;
 222         spin_unlock(&vnode->writeback_lock);
 223         SetPagePrivate(page);
 224         set_page_private(page, (unsigned long) wb);
 225         kfree(candidate);
 226         _leave(" = 0 [app]");
 227         return 0;
 228
 229         /* the page is currently bound to another context, so if it's dirty we
 230          * need to flush it before we can use the new context */
 231 flush_conflicting_wb:
 232         _debug("flush conflict");
 233         if (wb->state == AFS_WBACK_PENDING)
 234                 wb->state = AFS_WBACK_CONFLICTING;
 235         spin_unlock(&vnode->writeback_lock);
 236         if (PageDirty(page)) {
 237                 ret = afs_write_back_from_locked_page(wb, page);
 238                 if (ret < 0) {
 239                         afs_put_writeback(candidate);
 240                         _leave(" = %d", ret);
 241                         return ret;
 242                 }
 243         }
 244
 245         /* the page holds a ref on the writeback record */
 246         afs_put_writeback(wb);
 247         set_page_private(page, 0);
 248         ClearPagePrivate(page);
 249         goto try_again;
 250 }
 251
 252 /*
 253  * finalise part of a write to a page
 254  */
 255 int afs_write_end(struct file *file, struct address_space *mapping,
 256                   loff_t pos, unsigned len, unsigned copied,
 257                   struct page *page, void *fsdata)
 258 {
 259         struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
 260         loff_t i_size, maybe_i_size;
 261
 262         _enter("{%x:%u},{%lx}",
 263                vnode->fid.vid, vnode->fid.vnode, page->index);
 264
 265         maybe_i_size = pos + copied;
 266
 267         i_size = i_size_read(&vnode->vfs_inode);
 268         if (maybe_i_size > i_size) {
 269                 spin_lock(&vnode->writeback_lock);
 270                 i_size = i_size_read(&vnode->vfs_inode);
 271                 if (maybe_i_size > i_size)
 272                         i_size_write(&vnode->vfs_inode, maybe_i_size);
 273                 spin_unlock(&vnode->writeback_lock);
 274         }
 275
 276         set_page_dirty(page);
 277         if (PageDirty(page))
 278                 _debug("dirtied");
 279         unlock_page(page);
 280         put_page(page);
 281
 282         return copied;
 283 }
 284
 285 /*
 286  * kill all the pages in the given range
 287  */
 288 static void afs_kill_pages(struct afs_vnode *vnode, bool error,
 289                            pgoff_t first, pgoff_t last)
 290 {
 291         struct pagevec pv;
 292         unsigned count, loop;
 293
 294         _enter("{%x:%u},%lx-%lx",
 295                vnode->fid.vid, vnode->fid.vnode, first, last);
 296
 297         pagevec_init(&pv, 0);
 298
 299         do {
 300                 _debug("kill %lx-%lx", first, last);
 301
 302                 count = last - first + 1;
 303                 if (count > PAGEVEC_SIZE)
 304                         count = PAGEVEC_SIZE;
 305                 pv.nr = find_get_pages_contig(vnode->vfs_inode.i_mapping,
 306                                               first, count, pv.pages);
 307                 ASSERTCMP(pv.nr, ==, count);
 308
 309                 for (loop = 0; loop < count; loop++) {
 310                         ClearPageUptodate(pv.pages[loop]);
 311                         if (error)
 312                                 SetPageError(pv.pages[loop]);
 313                         end_page_writeback(pv.pages[loop]);
 314                 }
 315
 316                 __pagevec_release(&pv);
 317         } while (first < last);
 318
 319         _leave("");
 320 }
 321
 322 /*
 323  * synchronously write back the locked page and any subsequent non-locked dirty
 324  * pages also covered by the same writeback record
 325  */
 326 static int afs_write_back_from_locked_page(struct afs_writeback *wb,
 327                                            struct page *primary_page)
 328 {
 329         struct page *pages[8], *page;
 330         unsigned long count;
 331         unsigned n, offset, to;
 332         pgoff_t start, first, last;
 333         int loop, ret;
 334
 335         _enter(",%lx", primary_page->index);
 336
 337         count = 1;
 338         if (!clear_page_dirty_for_io(primary_page))
 339                 BUG();
 340         if (test_set_page_writeback(primary_page))
 341                 BUG();
 342
 343         /* find all consecutive lockable dirty pages, stopping when we find a
 344          * page that is not immediately lockable, is not dirty or is missing,
 345          * or we reach the end of the range */
 346         start = primary_page->index;
 347         if (start >= wb->last)
 348                 goto no_more;
 349         start++;
 350         do {
 351                 _debug("more %lx [%lx]", start, count);
 352                 n = wb->last - start + 1;
 353                 if (n > ARRAY_SIZE(pages))
 354                         n = ARRAY_SIZE(pages);
 355                 n = find_get_pages_contig(wb->vnode->vfs_inode.i_mapping,
 356                                           start, n, pages);
 357                 _debug("fgpc %u", n);
 358                 if (n == 0)
 359                         goto no_more;
 360                 if (pages[0]->index != start) {
 361                         do {
 362                                 put_page(pages[--n]);
 363                         } while (n > 0);
 364                         goto no_more;
 365                 }
 366
 367                 for (loop = 0; loop < n; loop++) {
 368                         page = pages[loop];
 369                         if (page->index > wb->last)
 370                                 break;
 371                         if (!trylock_page(page))
 372                                 break;
 373                         if (!PageDirty(page) ||
 374                             page_private(page) != (unsigned long) wb) {
 375                                 unlock_page(page);
 376                                 break;
 377                         }
 378                         if (!clear_page_dirty_for_io(page))
 379                                 BUG();
 380                         if (test_set_page_writeback(page))
 381                                 BUG();
 382                         unlock_page(page);
 383                         put_page(page);
 384                 }
 385                 count += loop;
 386                 if (loop < n) {
 387                         for (; loop < n; loop++)
 388                                 put_page(pages[loop]);
 389                         goto no_more;
 390                 }
 391
 392                 start += loop;
 393         } while (start <= wb->last && count < 65536);
 394
 395 no_more:
 396         /* we now have a contiguous set of dirty pages, each with writeback set
 397          * and the dirty mark cleared; the first page is locked and must remain
 398          * so, all the rest are unlocked */
 399         first = primary_page->index;
 400         last = first + count - 1;
 401
 402         offset = (first == wb->first) ? wb->offset_first : 0;
 403         to = (last == wb->last) ? wb->to_last : PAGE_SIZE;
 404
 405         _debug("write back %lx[%u..] to %lx[..%u]", first, offset, last, to);
 406
 407         ret = afs_vnode_store_data(wb, first, last, offset, to);
 408         if (ret < 0) {
 409                 switch (ret) {
 410                 case -EDQUOT:
 411                 case -ENOSPC:
 412                         mapping_set_error(wb->vnode->vfs_inode.i_mapping, -ENOSPC);
 413                         break;
 414                 case -EROFS:
 415                 case -EIO:
 416                 case -EREMOTEIO:
 417                 case -EFBIG:
 418                 case -ENOENT:
 419                 case -ENOMEDIUM:
 420                 case -ENXIO:
 421                         afs_kill_pages(wb->vnode, true, first, last);
 422                         mapping_set_error(wb->vnode->vfs_inode.i_mapping, -EIO);
 423                         break;
 424                 case -EACCES:
 425                 case -EPERM:
 426                 case -ENOKEY:
 427                 case -EKEYEXPIRED:
 428                 case -EKEYREJECTED:
 429                 case -EKEYREVOKED:
 430                         afs_kill_pages(wb->vnode, false, first, last);
 431                         break;
 432                 default:
 433                         break;
 434                 }
 435         } else {
 436                 ret = count;
 437         }
 438
 439         _leave(" = %d", ret);
 440         return ret;
 441 }
 442
 443 /*
 444  * write a page back to the server
 445  * - the caller locked the page for us
 446  */
 447 int afs_writepage(struct page *page, struct writeback_control *wbc)
 448 {
 449         struct afs_writeback *wb;
 450         int ret;
 451
 452         _enter("{%lx},", page->index);
 453
 454         wb = (struct afs_writeback *) page_private(page);
 455         ASSERT(wb != NULL);
 456
 457         ret = afs_write_back_from_locked_page(wb, page);
 458         unlock_page(page);
 459         if (ret < 0) {
 460                 _leave(" = %d", ret);
 461                 return 0;
 462         }
 463
 464         wbc->nr_to_write -= ret;
 465
 466         _leave(" = 0");
 467         return 0;
 468 }
 469
 470 /*
 471  * write a region of pages back to the server
 472  */
 473 static int afs_writepages_region(struct address_space *mapping,
 474                                  struct writeback_control *wbc,
 475                                  pgoff_t index, pgoff_t end, pgoff_t *_next)
 476 {
 477         struct afs_writeback *wb;
 478         struct page *page;
 479         int ret, n;
 480
 481         _enter(",,%lx,%lx,", index, end);
 482
 483         do {
 484                 n = find_get_pages_tag(mapping, &index, PAGECACHE_TAG_DIRTY,
 485                                        1, &page);
 486                 if (!n)
 487                         break;
 488
 489                 _debug("wback %lx", page->index);
 490
 491                 if (page->index > end) {
 492                         *_next = index;
 493                         put_page(page);
 494                         _leave(" = 0 [%lx]", *_next);
 495                         return 0;
 496                 }
 497
 498                 /* at this point we hold neither mapping->tree_lock nor lock on
 499                  * the page itself: the page may be truncated or invalidated
 500                  * (changing page->mapping to NULL), or even swizzled back from
 501                  * swapper_space to tmpfs file mapping
 502                  */
 503                 lock_page(page);
 504
 505                 if (page->mapping != mapping) {
 506                         unlock_page(page);
 507                         put_page(page);
 508                         continue;
 509                 }
 510
 511                 if (wbc->sync_mode != WB_SYNC_NONE)
 512                         wait_on_page_writeback(page);
 513
 514                 if (PageWriteback(page) || !PageDirty(page)) {
 515                         unlock_page(page);
 516                         continue;
 517                 }
 518
 519                 wb = (struct afs_writeback *) page_private(page);
 520                 ASSERT(wb != NULL);
 521
 522                 spin_lock(&wb->vnode->writeback_lock);
 523                 wb->state = AFS_WBACK_WRITING;
 524                 spin_unlock(&wb->vnode->writeback_lock);
 525
 526                 ret = afs_write_back_from_locked_page(wb, page);
 527                 unlock_page(page);
 528                 put_page(page);
 529                 if (ret < 0) {
 530                         _leave(" = %d", ret);
 531                         return ret;
 532                 }
 533
 534                 wbc->nr_to_write -= ret;
 535
 536                 cond_resched();
 537         } while (index < end && wbc->nr_to_write > 0);
 538
 539         *_next = index;
 540         _leave(" = 0 [%lx]", *_next);
 541         return 0;
 542 }
 543
 544 /*
 545  * write some of the pending data back to the server
 546  */
 547 int afs_writepages(struct address_space *mapping,
 548                    struct writeback_control *wbc)
 549 {
 550         pgoff_t start, end, next;
 551         int ret;
 552
 553         _enter("");
 554
 555         if (wbc->range_cyclic) {
 556                 start = mapping->writeback_index;
 557                 end = -1;
 558                 ret = afs_writepages_region(mapping, wbc, start, end, &next);
 559                 if (start > 0 && wbc->nr_to_write > 0 && ret == 0)
 560                         ret = afs_writepages_region(mapping, wbc, 0, start,
 561                                                     &next);
 562                 mapping->writeback_index = next;
 563         } else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
 564                 end = (pgoff_t)(LLONG_MAX >> PAGE_SHIFT);
 565                 ret = afs_writepages_region(mapping, wbc, 0, end, &next);
 566                 if (wbc->nr_to_write > 0)
 567                         mapping->writeback_index = next;
 568         } else {
 569                 start = wbc->range_start >> PAGE_SHIFT;
 570                 end = wbc->range_end >> PAGE_SHIFT;
 571                 ret = afs_writepages_region(mapping, wbc, start, end, &next);
 572         }
 573
 574         _leave(" = %d", ret);
 575         return ret;
 576 }
 577
 578 /*
 579  * completion of write to server
 580  */
 581 void afs_pages_written_back(struct afs_vnode *vnode, struct afs_call *call)
 582 {
 583         struct afs_writeback *wb = call->wb;
 584         struct pagevec pv;
 585         unsigned count, loop;
 586         pgoff_t first = call->first, last = call->last;
 587         bool free_wb;
 588
 589         _enter("{%x:%u},{%lx-%lx}",
 590                vnode->fid.vid, vnode->fid.vnode, first, last);
 591
 592         ASSERT(wb != NULL);
 593
 594         pagevec_init(&pv, 0);
 595
 596         do {
 597                 _debug("done %lx-%lx", first, last);
 598
 599                 count = last - first + 1;
 600                 if (count > PAGEVEC_SIZE)
 601                         count = PAGEVEC_SIZE;
 602                 pv.nr = find_get_pages_contig(call->mapping, first, count,
 603                                               pv.pages);
 604                 ASSERTCMP(pv.nr, ==, count);
 605
 606                 spin_lock(&vnode->writeback_lock);
 607                 for (loop = 0; loop < count; loop++) {
 608                         struct page *page = pv.pages[loop];
 609                         end_page_writeback(page);
 610                         if (page_private(page) == (unsigned long) wb) {
 611                                 set_page_private(page, 0);
 612                                 ClearPagePrivate(page);
 613                                 wb->usage--;
 614                         }
 615                 }
 616                 free_wb = false;
 617                 if (wb->usage == 0) {
 618                         afs_unlink_writeback(wb);
 619                         free_wb = true;
 620                 }
 621                 spin_unlock(&vnode->writeback_lock);
 622                 first += count;
 623                 if (free_wb) {
 624                         afs_free_writeback(wb);
 625                         wb = NULL;
 626                 }
 627
 628                 __pagevec_release(&pv);
 629         } while (first <= last);
 630
 631         _leave("");
 632 }
 633
 634 /*
 635  * write to an AFS file
 636  */
 637 ssize_t afs_file_write(struct kiocb *iocb, struct iov_iter *from)
 638 {
 639         struct afs_vnode *vnode = AFS_FS_I(file_inode(iocb->ki_filp));
 640         ssize_t result;
 641         size_t count = iov_iter_count(from);
 642
 643         _enter("{%x.%u},{%zu},",
 644                vnode->fid.vid, vnode->fid.vnode, count);
 645
 646         if (IS_SWAPFILE(&vnode->vfs_inode)) {
 647                 printk(KERN_INFO
 648                        "AFS: Attempt to write to active swap file!\n");
 649                 return -EBUSY;
 650         }
 651
 652         if (!count)
 653                 return 0;
 654
 655         result = generic_file_write_iter(iocb, from);
 656
 657         _leave(" = %zd", result);
 658         return result;
 659 }
 660
 661 /*
 662  * flush the vnode to the fileserver
 663  */
 664 int afs_writeback_all(struct afs_vnode *vnode)
 665 {
 666         struct address_space *mapping = vnode->vfs_inode.i_mapping;
 667         struct writeback_control wbc = {
 668                 .sync_mode      = WB_SYNC_ALL,
 669                 .nr_to_write    = LONG_MAX,
 670                 .range_cyclic   = 1,
 671         };
 672         int ret;
 673
 674         _enter("");
 675
 676         ret = mapping->a_ops->writepages(mapping, &wbc);
 677         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 678
 679         _leave(" = %d", ret);
 680         return ret;
 681 }
 682
 683 /*
 684  * flush any dirty pages for this process, and check for write errors.
 685  * - the return status from this call provides a reliable indication of
 686  *   whether any write errors occurred for this process.
 687  */
 688 int afs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 689 {
 690         struct inode *inode = file_inode(file);
 691         struct afs_writeback *wb, *xwb;
 692         struct afs_vnode *vnode = AFS_FS_I(inode);
 693         int ret;
 694
 695         _enter("{%x:%u},{n=%pD},%d",
 696                vnode->fid.vid, vnode->fid.vnode, file,
 697                datasync);
 698
 699         ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
 700         if (ret)
 701                 return ret;
 702         inode_lock(inode);
 703
 704         /* use a writeback record as a marker in the queue - when this reaches
 705          * the front of the queue, all the outstanding writes are either
 706          * completed or rejected */
 707         wb = kzalloc(sizeof(*wb), GFP_KERNEL);
 708         if (!wb) {
 709                 ret = -ENOMEM;
 710                 goto out;
 711         }
 712         wb->vnode = vnode;
 713         wb->first = 0;
 714         wb->last = -1;
 715         wb->offset_first = 0;
 716         wb->to_last = PAGE_SIZE;
 717         wb->usage = 1;
 718         wb->state = AFS_WBACK_SYNCING;
 719         init_waitqueue_head(&wb->waitq);
 720
 721         spin_lock(&vnode->writeback_lock);
 722         list_for_each_entry(xwb, &vnode->writebacks, link) {
 723                 if (xwb->state == AFS_WBACK_PENDING)
 724                         xwb->state = AFS_WBACK_CONFLICTING;
 725         }
 726         list_add_tail(&wb->link, &vnode->writebacks);
 727         spin_unlock(&vnode->writeback_lock);
 728
 729         /* push all the outstanding writebacks to the server */
 730         ret = afs_writeback_all(vnode);
 731         if (ret < 0) {
 732                 afs_put_writeback(wb);
 733                 _leave(" = %d [wb]", ret);
 734                 goto out;
 735         }
 736
 737         /* wait for the preceding writes to actually complete */
 738         ret = wait_event_interruptible(wb->waitq,
 739                                        wb->state == AFS_WBACK_COMPLETE ||
 740                                        vnode->writebacks.next == &wb->link);
 741         afs_put_writeback(wb);
 742         _leave(" = %d", ret);
 743 out:
 744         inode_unlock(inode);
 745         return ret;
 746 }
 747
 748 /*
 749  * notification that a previously read-only page is about to become writable
 750  * - if it returns an error, the caller will deliver a bus error signal
 751  */
 752 int afs_page_mkwrite(struct vm_area_struct *vma, struct page *page)
 753 {
 754         struct afs_vnode *vnode = AFS_FS_I(vma->vm_file->f_mapping->host);
 755
 756         _enter("{{%x:%u}},{%lx}",
 757                vnode->fid.vid, vnode->fid.vnode, page->index);
 758
 759         /* wait for the page to be written to the cache before we allow it to
 760          * be modified */
 761 #ifdef CONFIG_AFS_FSCACHE
 762         fscache_wait_on_page_write(vnode->cache, page);
 763 #endif
 764
 765         _leave(" = 0");
 766         return 0;
 767 }