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    Subject[023/165] ext4: dont set PageUptodate in ext4_end_bio()
    2.6.39-stable review patch.  If anyone has any objections, please let us know.

    ------------------
    Content-Length: 3118
    Lines: 99

    From: Curt Wohlgemuth <curtw@google.com>

    commit 39db00f1c45e770856264bdb3ceca27980b01965 upstream.

    In the bio completion routine, we should not be setting
    PageUptodate at all -- it's set at sys_write() time, and is
    unaffected by success/failure of the write to disk.

    This can cause a page corruption bug when the file system's
    block size is less than the architecture's VM page size.

    if we have only written a single block -- we might end up
    setting the page's PageUptodate flag, indicating that page
    is completely read into memory, which may not be true.
    This could cause subsequent reads to get bad data.

    This commit also takes the opportunity to clean up error
    handling in ext4_end_bio(), and remove some extraneous code:

    - fixes ext4_end_bio() to set AS_EIO in the
    page->mapping->flags on error, which was left out by
    mistake. This is needed so that fsync() will
    return an error if there was an I/O error.
    - remove the clear_buffer_dirty() call on unmapped
    buffers for each page.
    - consolidate page/buffer error handling in a single
    section.

    Signed-off-by: Curt Wohlgemuth <curtw@google.com>
    Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
    Reported-by: Jim Meyering <jim@meyering.net>
    Reported-by: Hugh Dickins <hughd@google.com>
    Cc: Mingming Cao <cmm@us.ibm.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    fs/ext4/page-io.c | 37 ++++++++++---------------------------
    1 file changed, 10 insertions(+), 27 deletions(-)

    --- a/fs/ext4/page-io.c
    +++ b/fs/ext4/page-io.c
    @@ -203,46 +203,29 @@ static void ext4_end_bio(struct bio *bio
    for (i = 0; i < io_end->num_io_pages; i++) {
    struct page *page = io_end->pages[i]->p_page;
    struct buffer_head *bh, *head;
    - int partial_write = 0;
    + loff_t offset;
    + loff_t io_end_offset;

    - head = page_buffers(page);
    - if (error)
    + if (error) {
    SetPageError(page);
    - BUG_ON(!head);
    - if (head->b_size != PAGE_CACHE_SIZE) {
    - loff_t offset;
    - loff_t io_end_offset = io_end->offset + io_end->size;
    + set_bit(AS_EIO, &page->mapping->flags);
    + head = page_buffers(page);
    + BUG_ON(!head);
    +
    + io_end_offset = io_end->offset + io_end->size;

    offset = (sector_t) page->index << PAGE_CACHE_SHIFT;
    bh = head;
    do {
    if ((offset >= io_end->offset) &&
    - (offset+bh->b_size <= io_end_offset)) {
    - if (error)
    - buffer_io_error(bh);
    + (offset+bh->b_size <= io_end_offset))
    + buffer_io_error(bh);

    - }
    - if (buffer_delay(bh))
    - partial_write = 1;
    - else if (!buffer_mapped(bh))
    - clear_buffer_dirty(bh);
    - else if (buffer_dirty(bh))
    - partial_write = 1;
    offset += bh->b_size;
    bh = bh->b_this_page;
    } while (bh != head);
    }

    - /*
    - * If this is a partial write which happened to make
    - * all buffers uptodate then we can optimize away a
    - * bogus readpage() for the next read(). Here we
    - * 'discover' whether the page went uptodate as a
    - * result of this (potentially partial) write.
    - */
    - if (!partial_write)
    - SetPageUptodate(page);
    -
    put_io_page(io_end->pages[i]);
    }
    io_end->num_io_pages = 0;



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