[PATCH] mpage_writepages() page locking fix
[linux-2.6.git] / fs / mpage.c
1 /*
2  * fs/mpage.c
3  *
4  * Copyright (C) 2002, Linus Torvalds.
5  *
6  * Contains functions related to preparing and submitting BIOs which contain
7  * multiple pagecache pages.
8  *
9  * 15May2002    akpm@zip.com.au
10  *              Initial version
11  * 27Jun2002    axboe@suse.de
12  *              use bio_add_page() to build bio's just the right size
13  */
14
15 #include <linux/kernel.h>
16 #include <linux/module.h>
17 #include <linux/mm.h>
18 #include <linux/kdev_t.h>
19 #include <linux/bio.h>
20 #include <linux/fs.h>
21 #include <linux/buffer_head.h>
22 #include <linux/blkdev.h>
23 #include <linux/highmem.h>
24 #include <linux/prefetch.h>
25 #include <linux/mpage.h>
26 #include <linux/writeback.h>
27 #include <linux/backing-dev.h>
28 #include <linux/pagevec.h>
29
30 /*
31  * I/O completion handler for multipage BIOs.
32  *
33  * The mpage code never puts partial pages into a BIO (except for end-of-file).
34  * If a page does not map to a contiguous run of blocks then it simply falls
35  * back to block_read_full_page().
36  *
37  * Why is this?  If a page's completion depends on a number of different BIOs
38  * which can complete in any order (or at the same time) then determining the
39  * status of that page is hard.  See end_buffer_async_read() for the details.
40  * There is no point in duplicating all that complexity.
41  */
42 static int mpage_end_io_read(struct bio *bio, unsigned int bytes_done, int err)
43 {
44         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
45         struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
46
47         if (bio->bi_size)
48                 return 1;
49
50         do {
51                 struct page *page = bvec->bv_page;
52
53                 if (--bvec >= bio->bi_io_vec)
54                         prefetchw(&bvec->bv_page->flags);
55
56                 if (uptodate) {
57                         SetPageUptodate(page);
58                 } else {
59                         ClearPageUptodate(page);
60                         SetPageError(page);
61                 }
62                 unlock_page(page);
63         } while (bvec >= bio->bi_io_vec);
64         bio_put(bio);
65         return 0;
66 }
67
68 static int mpage_end_io_write(struct bio *bio, unsigned int bytes_done, int err)
69 {
70         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
71         struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
72
73         if (bio->bi_size)
74                 return 1;
75
76         do {
77                 struct page *page = bvec->bv_page;
78
79                 if (--bvec >= bio->bi_io_vec)
80                         prefetchw(&bvec->bv_page->flags);
81
82                 if (!uptodate)
83                         SetPageError(page);
84                 end_page_writeback(page);
85         } while (bvec >= bio->bi_io_vec);
86         bio_put(bio);
87         return 0;
88 }
89
90 struct bio *mpage_bio_submit(int rw, struct bio *bio)
91 {
92         bio->bi_end_io = mpage_end_io_read;
93         if (rw == WRITE)
94                 bio->bi_end_io = mpage_end_io_write;
95         submit_bio(rw, bio);
96         return NULL;
97 }
98
99 static struct bio *
100 mpage_alloc(struct block_device *bdev,
101                 sector_t first_sector, int nr_vecs,
102                 unsigned int __nocast gfp_flags)
103 {
104         struct bio *bio;
105
106         bio = bio_alloc(gfp_flags, nr_vecs);
107
108         if (bio == NULL && (current->flags & PF_MEMALLOC)) {
109                 while (!bio && (nr_vecs /= 2))
110                         bio = bio_alloc(gfp_flags, nr_vecs);
111         }
112
113         if (bio) {
114                 bio->bi_bdev = bdev;
115                 bio->bi_sector = first_sector;
116         }
117         return bio;
118 }
119
120 /*
121  * support function for mpage_readpages.  The fs supplied get_block might
122  * return an up to date buffer.  This is used to map that buffer into
123  * the page, which allows readpage to avoid triggering a duplicate call
124  * to get_block.
125  *
126  * The idea is to avoid adding buffers to pages that don't already have
127  * them.  So when the buffer is up to date and the page size == block size,
128  * this marks the page up to date instead of adding new buffers.
129  */
130 static void 
131 map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block) 
132 {
133         struct inode *inode = page->mapping->host;
134         struct buffer_head *page_bh, *head;
135         int block = 0;
136
137         if (!page_has_buffers(page)) {
138                 /*
139                  * don't make any buffers if there is only one buffer on
140                  * the page and the page just needs to be set up to date
141                  */
142                 if (inode->i_blkbits == PAGE_CACHE_SHIFT && 
143                     buffer_uptodate(bh)) {
144                         SetPageUptodate(page);    
145                         return;
146                 }
147                 create_empty_buffers(page, 1 << inode->i_blkbits, 0);
148         }
149         head = page_buffers(page);
150         page_bh = head;
151         do {
152                 if (block == page_block) {
153                         page_bh->b_state = bh->b_state;
154                         page_bh->b_bdev = bh->b_bdev;
155                         page_bh->b_blocknr = bh->b_blocknr;
156                         break;
157                 }
158                 page_bh = page_bh->b_this_page;
159                 block++;
160         } while (page_bh != head);
161 }
162
163 /**
164  * mpage_readpages - populate an address space with some pages, and
165  *                       start reads against them.
166  *
167  * @mapping: the address_space
168  * @pages: The address of a list_head which contains the target pages.  These
169  *   pages have their ->index populated and are otherwise uninitialised.
170  *
171  *   The page at @pages->prev has the lowest file offset, and reads should be
172  *   issued in @pages->prev to @pages->next order.
173  *
174  * @nr_pages: The number of pages at *@pages
175  * @get_block: The filesystem's block mapper function.
176  *
177  * This function walks the pages and the blocks within each page, building and
178  * emitting large BIOs.
179  *
180  * If anything unusual happens, such as:
181  *
182  * - encountering a page which has buffers
183  * - encountering a page which has a non-hole after a hole
184  * - encountering a page with non-contiguous blocks
185  *
186  * then this code just gives up and calls the buffer_head-based read function.
187  * It does handle a page which has holes at the end - that is a common case:
188  * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
189  *
190  * BH_Boundary explanation:
191  *
192  * There is a problem.  The mpage read code assembles several pages, gets all
193  * their disk mappings, and then submits them all.  That's fine, but obtaining
194  * the disk mappings may require I/O.  Reads of indirect blocks, for example.
195  *
196  * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
197  * submitted in the following order:
198  *      12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
199  * because the indirect block has to be read to get the mappings of blocks
200  * 13,14,15,16.  Obviously, this impacts performance.
201  * 
202  * So what we do it to allow the filesystem's get_block() function to set
203  * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
204  * after this one will require I/O against a block which is probably close to
205  * this one.  So you should push what I/O you have currently accumulated.
206  *
207  * This all causes the disk requests to be issued in the correct order.
208  */
209 static struct bio *
210 do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
211                         sector_t *last_block_in_bio, get_block_t get_block)
212 {
213         struct inode *inode = page->mapping->host;
214         const unsigned blkbits = inode->i_blkbits;
215         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
216         const unsigned blocksize = 1 << blkbits;
217         sector_t block_in_file;
218         sector_t last_block;
219         sector_t blocks[MAX_BUF_PER_PAGE];
220         unsigned page_block;
221         unsigned first_hole = blocks_per_page;
222         struct block_device *bdev = NULL;
223         struct buffer_head bh;
224         int length;
225         int fully_mapped = 1;
226
227         if (page_has_buffers(page))
228                 goto confused;
229
230         block_in_file = page->index << (PAGE_CACHE_SHIFT - blkbits);
231         last_block = (i_size_read(inode) + blocksize - 1) >> blkbits;
232
233         bh.b_page = page;
234         for (page_block = 0; page_block < blocks_per_page;
235                                 page_block++, block_in_file++) {
236                 bh.b_state = 0;
237                 if (block_in_file < last_block) {
238                         if (get_block(inode, block_in_file, &bh, 0))
239                                 goto confused;
240                 }
241
242                 if (!buffer_mapped(&bh)) {
243                         fully_mapped = 0;
244                         if (first_hole == blocks_per_page)
245                                 first_hole = page_block;
246                         continue;
247                 }
248
249                 /* some filesystems will copy data into the page during
250                  * the get_block call, in which case we don't want to
251                  * read it again.  map_buffer_to_page copies the data
252                  * we just collected from get_block into the page's buffers
253                  * so readpage doesn't have to repeat the get_block call
254                  */
255                 if (buffer_uptodate(&bh)) {
256                         map_buffer_to_page(page, &bh, page_block);
257                         goto confused;
258                 }
259         
260                 if (first_hole != blocks_per_page)
261                         goto confused;          /* hole -> non-hole */
262
263                 /* Contiguous blocks? */
264                 if (page_block && blocks[page_block-1] != bh.b_blocknr-1)
265                         goto confused;
266                 blocks[page_block] = bh.b_blocknr;
267                 bdev = bh.b_bdev;
268         }
269
270         if (first_hole != blocks_per_page) {
271                 char *kaddr = kmap_atomic(page, KM_USER0);
272                 memset(kaddr + (first_hole << blkbits), 0,
273                                 PAGE_CACHE_SIZE - (first_hole << blkbits));
274                 flush_dcache_page(page);
275                 kunmap_atomic(kaddr, KM_USER0);
276                 if (first_hole == 0) {
277                         SetPageUptodate(page);
278                         unlock_page(page);
279                         goto out;
280                 }
281         } else if (fully_mapped) {
282                 SetPageMappedToDisk(page);
283         }
284
285         /*
286          * This page will go to BIO.  Do we need to send this BIO off first?
287          */
288         if (bio && (*last_block_in_bio != blocks[0] - 1))
289                 bio = mpage_bio_submit(READ, bio);
290
291 alloc_new:
292         if (bio == NULL) {
293                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
294                                 min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
295                                 GFP_KERNEL);
296                 if (bio == NULL)
297                         goto confused;
298         }
299
300         length = first_hole << blkbits;
301         if (bio_add_page(bio, page, length, 0) < length) {
302                 bio = mpage_bio_submit(READ, bio);
303                 goto alloc_new;
304         }
305
306         if (buffer_boundary(&bh) || (first_hole != blocks_per_page))
307                 bio = mpage_bio_submit(READ, bio);
308         else
309                 *last_block_in_bio = blocks[blocks_per_page - 1];
310 out:
311         return bio;
312
313 confused:
314         if (bio)
315                 bio = mpage_bio_submit(READ, bio);
316         if (!PageUptodate(page))
317                 block_read_full_page(page, get_block);
318         else
319                 unlock_page(page);
320         goto out;
321 }
322
323 int
324 mpage_readpages(struct address_space *mapping, struct list_head *pages,
325                                 unsigned nr_pages, get_block_t get_block)
326 {
327         struct bio *bio = NULL;
328         unsigned page_idx;
329         sector_t last_block_in_bio = 0;
330         struct pagevec lru_pvec;
331
332         pagevec_init(&lru_pvec, 0);
333         for (page_idx = 0; page_idx < nr_pages; page_idx++) {
334                 struct page *page = list_entry(pages->prev, struct page, lru);
335
336                 prefetchw(&page->flags);
337                 list_del(&page->lru);
338                 if (!add_to_page_cache(page, mapping,
339                                         page->index, GFP_KERNEL)) {
340                         bio = do_mpage_readpage(bio, page,
341                                         nr_pages - page_idx,
342                                         &last_block_in_bio, get_block);
343                         if (!pagevec_add(&lru_pvec, page))
344                                 __pagevec_lru_add(&lru_pvec);
345                 } else {
346                         page_cache_release(page);
347                 }
348         }
349         pagevec_lru_add(&lru_pvec);
350         BUG_ON(!list_empty(pages));
351         if (bio)
352                 mpage_bio_submit(READ, bio);
353         return 0;
354 }
355 EXPORT_SYMBOL(mpage_readpages);
356
357 /*
358  * This isn't called much at all
359  */
360 int mpage_readpage(struct page *page, get_block_t get_block)
361 {
362         struct bio *bio = NULL;
363         sector_t last_block_in_bio = 0;
364
365         bio = do_mpage_readpage(bio, page, 1,
366                         &last_block_in_bio, get_block);
367         if (bio)
368                 mpage_bio_submit(READ, bio);
369         return 0;
370 }
371 EXPORT_SYMBOL(mpage_readpage);
372
373 /*
374  * Writing is not so simple.
375  *
376  * If the page has buffers then they will be used for obtaining the disk
377  * mapping.  We only support pages which are fully mapped-and-dirty, with a
378  * special case for pages which are unmapped at the end: end-of-file.
379  *
380  * If the page has no buffers (preferred) then the page is mapped here.
381  *
382  * If all blocks are found to be contiguous then the page can go into the
383  * BIO.  Otherwise fall back to the mapping's writepage().
384  * 
385  * FIXME: This code wants an estimate of how many pages are still to be
386  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
387  * just allocate full-size (16-page) BIOs.
388  */
389 static struct bio *
390 __mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
391         sector_t *last_block_in_bio, int *ret, struct writeback_control *wbc,
392         writepage_t writepage_fn)
393 {
394         struct address_space *mapping = page->mapping;
395         struct inode *inode = page->mapping->host;
396         const unsigned blkbits = inode->i_blkbits;
397         unsigned long end_index;
398         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
399         sector_t last_block;
400         sector_t block_in_file;
401         sector_t blocks[MAX_BUF_PER_PAGE];
402         unsigned page_block;
403         unsigned first_unmapped = blocks_per_page;
404         struct block_device *bdev = NULL;
405         int boundary = 0;
406         sector_t boundary_block = 0;
407         struct block_device *boundary_bdev = NULL;
408         int length;
409         struct buffer_head map_bh;
410         loff_t i_size = i_size_read(inode);
411
412         if (page_has_buffers(page)) {
413                 struct buffer_head *head = page_buffers(page);
414                 struct buffer_head *bh = head;
415
416                 /* If they're all mapped and dirty, do it */
417                 page_block = 0;
418                 do {
419                         BUG_ON(buffer_locked(bh));
420                         if (!buffer_mapped(bh)) {
421                                 /*
422                                  * unmapped dirty buffers are created by
423                                  * __set_page_dirty_buffers -> mmapped data
424                                  */
425                                 if (buffer_dirty(bh))
426                                         goto confused;
427                                 if (first_unmapped == blocks_per_page)
428                                         first_unmapped = page_block;
429                                 continue;
430                         }
431
432                         if (first_unmapped != blocks_per_page)
433                                 goto confused;  /* hole -> non-hole */
434
435                         if (!buffer_dirty(bh) || !buffer_uptodate(bh))
436                                 goto confused;
437                         if (page_block) {
438                                 if (bh->b_blocknr != blocks[page_block-1] + 1)
439                                         goto confused;
440                         }
441                         blocks[page_block++] = bh->b_blocknr;
442                         boundary = buffer_boundary(bh);
443                         if (boundary) {
444                                 boundary_block = bh->b_blocknr;
445                                 boundary_bdev = bh->b_bdev;
446                         }
447                         bdev = bh->b_bdev;
448                 } while ((bh = bh->b_this_page) != head);
449
450                 if (first_unmapped)
451                         goto page_is_mapped;
452
453                 /*
454                  * Page has buffers, but they are all unmapped. The page was
455                  * created by pagein or read over a hole which was handled by
456                  * block_read_full_page().  If this address_space is also
457                  * using mpage_readpages then this can rarely happen.
458                  */
459                 goto confused;
460         }
461
462         /*
463          * The page has no buffers: map it to disk
464          */
465         BUG_ON(!PageUptodate(page));
466         block_in_file = page->index << (PAGE_CACHE_SHIFT - blkbits);
467         last_block = (i_size - 1) >> blkbits;
468         map_bh.b_page = page;
469         for (page_block = 0; page_block < blocks_per_page; ) {
470
471                 map_bh.b_state = 0;
472                 if (get_block(inode, block_in_file, &map_bh, 1))
473                         goto confused;
474                 if (buffer_new(&map_bh))
475                         unmap_underlying_metadata(map_bh.b_bdev,
476                                                 map_bh.b_blocknr);
477                 if (buffer_boundary(&map_bh)) {
478                         boundary_block = map_bh.b_blocknr;
479                         boundary_bdev = map_bh.b_bdev;
480                 }
481                 if (page_block) {
482                         if (map_bh.b_blocknr != blocks[page_block-1] + 1)
483                                 goto confused;
484                 }
485                 blocks[page_block++] = map_bh.b_blocknr;
486                 boundary = buffer_boundary(&map_bh);
487                 bdev = map_bh.b_bdev;
488                 if (block_in_file == last_block)
489                         break;
490                 block_in_file++;
491         }
492         BUG_ON(page_block == 0);
493
494         first_unmapped = page_block;
495
496 page_is_mapped:
497         end_index = i_size >> PAGE_CACHE_SHIFT;
498         if (page->index >= end_index) {
499                 /*
500                  * The page straddles i_size.  It must be zeroed out on each
501                  * and every writepage invokation because it may be mmapped.
502                  * "A file is mapped in multiples of the page size.  For a file
503                  * that is not a multiple of the page size, the remaining memory
504                  * is zeroed when mapped, and writes to that region are not
505                  * written out to the file."
506                  */
507                 unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);
508                 char *kaddr;
509
510                 if (page->index > end_index || !offset)
511                         goto confused;
512                 kaddr = kmap_atomic(page, KM_USER0);
513                 memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
514                 flush_dcache_page(page);
515                 kunmap_atomic(kaddr, KM_USER0);
516         }
517
518         /*
519          * This page will go to BIO.  Do we need to send this BIO off first?
520          */
521         if (bio && *last_block_in_bio != blocks[0] - 1)
522                 bio = mpage_bio_submit(WRITE, bio);
523
524 alloc_new:
525         if (bio == NULL) {
526                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
527                                 bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
528                 if (bio == NULL)
529                         goto confused;
530         }
531
532         /*
533          * Must try to add the page before marking the buffer clean or
534          * the confused fail path above (OOM) will be very confused when
535          * it finds all bh marked clean (i.e. it will not write anything)
536          */
537         length = first_unmapped << blkbits;
538         if (bio_add_page(bio, page, length, 0) < length) {
539                 bio = mpage_bio_submit(WRITE, bio);
540                 goto alloc_new;
541         }
542
543         /*
544          * OK, we have our BIO, so we can now mark the buffers clean.  Make
545          * sure to only clean buffers which we know we'll be writing.
546          */
547         if (page_has_buffers(page)) {
548                 struct buffer_head *head = page_buffers(page);
549                 struct buffer_head *bh = head;
550                 unsigned buffer_counter = 0;
551
552                 do {
553                         if (buffer_counter++ == first_unmapped)
554                                 break;
555                         clear_buffer_dirty(bh);
556                         bh = bh->b_this_page;
557                 } while (bh != head);
558
559                 /*
560                  * we cannot drop the bh if the page is not uptodate
561                  * or a concurrent readpage would fail to serialize with the bh
562                  * and it would read from disk before we reach the platter.
563                  */
564                 if (buffer_heads_over_limit && PageUptodate(page))
565                         try_to_free_buffers(page);
566         }
567
568         BUG_ON(PageWriteback(page));
569         set_page_writeback(page);
570         unlock_page(page);
571         if (boundary || (first_unmapped != blocks_per_page)) {
572                 bio = mpage_bio_submit(WRITE, bio);
573                 if (boundary_block) {
574                         write_boundary_block(boundary_bdev,
575                                         boundary_block, 1 << blkbits);
576                 }
577         } else {
578                 *last_block_in_bio = blocks[blocks_per_page - 1];
579         }
580         goto out;
581
582 confused:
583         if (bio)
584                 bio = mpage_bio_submit(WRITE, bio);
585
586         if (writepage_fn) {
587                 *ret = (*writepage_fn)(page, wbc);
588         } else {
589                 *ret = -EAGAIN;
590                 goto out;
591         }
592         /*
593          * The caller has a ref on the inode, so *mapping is stable
594          */
595         if (*ret) {
596                 if (*ret == -ENOSPC)
597                         set_bit(AS_ENOSPC, &mapping->flags);
598                 else
599                         set_bit(AS_EIO, &mapping->flags);
600         }
601 out:
602         return bio;
603 }
604
605 /**
606  * mpage_writepages - walk the list of dirty pages of the given
607  * address space and writepage() all of them.
608  * 
609  * @mapping: address space structure to write
610  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
611  * @get_block: the filesystem's block mapper function.
612  *             If this is NULL then use a_ops->writepage.  Otherwise, go
613  *             direct-to-BIO.
614  *
615  * This is a library function, which implements the writepages()
616  * address_space_operation.
617  *
618  * If a page is already under I/O, generic_writepages() skips it, even
619  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
620  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
621  * and msync() need to guarantee that all the data which was dirty at the time
622  * the call was made get new I/O started against them.  If wbc->sync_mode is
623  * WB_SYNC_ALL then we were called for data integrity and we must wait for
624  * existing IO to complete.
625  */
626 int
627 mpage_writepages(struct address_space *mapping,
628                 struct writeback_control *wbc, get_block_t get_block)
629 {
630         return __mpage_writepages(mapping, wbc, get_block,
631                 mapping->a_ops->writepage);
632 }
633
634 int
635 __mpage_writepages(struct address_space *mapping,
636                 struct writeback_control *wbc, get_block_t get_block,
637                 writepage_t writepage_fn)
638 {
639         struct backing_dev_info *bdi = mapping->backing_dev_info;
640         struct bio *bio = NULL;
641         sector_t last_block_in_bio = 0;
642         int ret = 0;
643         int done = 0;
644         int (*writepage)(struct page *page, struct writeback_control *wbc);
645         struct pagevec pvec;
646         int nr_pages;
647         pgoff_t index;
648         pgoff_t end = -1;               /* Inclusive */
649         int scanned = 0;
650         int is_range = 0;
651
652         if (wbc->nonblocking && bdi_write_congested(bdi)) {
653                 wbc->encountered_congestion = 1;
654                 return 0;
655         }
656
657         writepage = NULL;
658         if (get_block == NULL)
659                 writepage = mapping->a_ops->writepage;
660
661         pagevec_init(&pvec, 0);
662         if (wbc->sync_mode == WB_SYNC_NONE) {
663                 index = mapping->writeback_index; /* Start from prev offset */
664         } else {
665                 index = 0;                        /* whole-file sweep */
666                 scanned = 1;
667         }
668         if (wbc->start || wbc->end) {
669                 index = wbc->start >> PAGE_CACHE_SHIFT;
670                 end = wbc->end >> PAGE_CACHE_SHIFT;
671                 is_range = 1;
672                 scanned = 1;
673         }
674 retry:
675         while (!done && (index <= end) &&
676                         (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
677                         PAGECACHE_TAG_DIRTY,
678                         min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
679                 unsigned i;
680
681                 scanned = 1;
682                 for (i = 0; i < nr_pages; i++) {
683                         struct page *page = pvec.pages[i];
684
685                         /*
686                          * At this point we hold neither mapping->tree_lock nor
687                          * lock on the page itself: the page may be truncated or
688                          * invalidated (changing page->mapping to NULL), or even
689                          * swizzled back from swapper_space to tmpfs file
690                          * mapping
691                          */
692
693                         lock_page(page);
694
695                         if (unlikely(page->mapping != mapping)) {
696                                 unlock_page(page);
697                                 continue;
698                         }
699
700                         if (unlikely(is_range) && page->index > end) {
701                                 done = 1;
702                                 unlock_page(page);
703                                 continue;
704                         }
705
706                         if (wbc->sync_mode != WB_SYNC_NONE)
707                                 wait_on_page_writeback(page);
708
709                         if (PageWriteback(page) ||
710                                         !clear_page_dirty_for_io(page)) {
711                                 unlock_page(page);
712                                 continue;
713                         }
714
715                         if (writepage) {
716                                 ret = (*writepage)(page, wbc);
717                                 if (ret) {
718                                         if (ret == -ENOSPC)
719                                                 set_bit(AS_ENOSPC,
720                                                         &mapping->flags);
721                                         else
722                                                 set_bit(AS_EIO,
723                                                         &mapping->flags);
724                                 }
725                         } else {
726                                 bio = __mpage_writepage(bio, page, get_block,
727                                                 &last_block_in_bio, &ret, wbc,
728                                                 writepage_fn);
729                         }
730                         if (unlikely(ret == WRITEPAGE_ACTIVATE))
731                                 unlock_page(page);
732                         if (ret || (--(wbc->nr_to_write) <= 0))
733                                 done = 1;
734                         if (wbc->nonblocking && bdi_write_congested(bdi)) {
735                                 wbc->encountered_congestion = 1;
736                                 done = 1;
737                         }
738                 }
739                 pagevec_release(&pvec);
740                 cond_resched();
741         }
742         if (!scanned && !done) {
743                 /*
744                  * We hit the last page and there is more work to be done: wrap
745                  * back to the start of the file
746                  */
747                 scanned = 1;
748                 index = 0;
749                 goto retry;
750         }
751         if (!is_range)
752                 mapping->writeback_index = index;
753         if (bio)
754                 mpage_bio_submit(WRITE, bio);
755         return ret;
756 }
757 EXPORT_SYMBOL(mpage_writepages);
758 EXPORT_SYMBOL(__mpage_writepages);
759
760 int mpage_writepage(struct page *page, get_block_t get_block,
761         struct writeback_control *wbc)
762 {
763         int ret = 0;
764         struct bio *bio;
765         sector_t last_block_in_bio = 0;
766
767         bio = __mpage_writepage(NULL, page, get_block,
768                         &last_block_in_bio, &ret, wbc, NULL);
769         if (bio)
770                 mpage_bio_submit(WRITE, bio);
771
772         return ret;
773 }
774 EXPORT_SYMBOL(mpage_writepage);