VServer 1.9.2 (patch-2.6.8.1-vs1.9.2.diff)

[linux-2.6.git] / fs / mpage.c

diff --git a/fs/mpage.c b/fs/mpage.c
index a22fc8f..71c7ca3 100644 (file)
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -404,6 +404,7 @@ mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
        struct block_device *boundary_bdev = NULL;
        int length;
        struct buffer_head map_bh;
+       loff_t i_size = i_size_read(inode);
 
        if (page_has_buffers(page)) {
                struct buffer_head *head = page_buffers(page);
@@ -460,7 +461,7 @@ mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
         */
        BUG_ON(!PageUptodate(page));
        block_in_file = page->index << (PAGE_CACHE_SHIFT - blkbits);
-       last_block = (i_size_read(inode) - 1) >> blkbits;
+       last_block = (i_size - 1) >> blkbits;
        map_bh.b_page = page;
        for (page_block = 0; page_block < blocks_per_page; ) {
 
@@ -489,9 +490,18 @@ mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
 
        first_unmapped = page_block;
 
-       end_index = i_size_read(inode) >> PAGE_CACHE_SHIFT;
+page_is_mapped:
+       end_index = i_size >> PAGE_CACHE_SHIFT;
        if (page->index >= end_index) {
-               unsigned offset = i_size_read(inode) & (PAGE_CACHE_SIZE - 1);
+               /*
+                * The page straddles i_size.  It must be zeroed out on each
+                * and every writepage invokation because it may be mmapped.
+                * "A file is mapped in multiples of the page size.  For a file
+                * that is not a multiple of the page size, the remaining memory
+                * is zeroed when mapped, and writes to that region are not
+                * written out to the file."
+                */
+               unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);
                char *kaddr;
 
                if (page->index > end_index || !offset)
@@ -502,8 +512,6 @@ mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
                kunmap_atomic(kaddr, KM_USER0);
        }
 
-page_is_mapped:
-
        /*
         * This page will go to BIO.  Do we need to send this BIO off first?
         */
@@ -518,6 +526,17 @@ alloc_new:
                        goto confused;
        }
 
+       /*
+        * Must try to add the page before marking the buffer clean or
+        * the confused fail path above (OOM) will be very confused when
+        * it finds all bh marked clean (i.e. it will not write anything)
+        */
+       length = first_unmapped << blkbits;
+       if (bio_add_page(bio, page, length, 0) < length) {
+               bio = mpage_bio_submit(WRITE, bio);
+               goto alloc_new;
+       }
+
        /*
         * OK, we have our BIO, so we can now mark the buffers clean.  Make
         * sure to only clean buffers which we know we'll be writing.
@@ -534,16 +553,15 @@ alloc_new:
                        bh = bh->b_this_page;
                } while (bh != head);
 
-               if (buffer_heads_over_limit)
+               /*
+                * we cannot drop the bh if the page is not uptodate
+                * or a concurrent readpage would fail to serialize with the bh
+                * and it would read from disk before we reach the platter.
+                */
+               if (buffer_heads_over_limit && PageUptodate(page))
                        try_to_free_buffers(page);
        }
 
-       length = first_unmapped << blkbits;
-       if (bio_add_page(bio, page, length, 0) < length) {
-               bio = mpage_bio_submit(WRITE, bio);
-               goto alloc_new;
-       }
-
        BUG_ON(PageWriteback(page));
        set_page_writeback(page);
        unlock_page(page);