On Mon, 25 Apr 2011, Curt Wohlgemuth wrote:
> 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
>
> block size < page size
>
> if we have only written a single block -- we might end up
> setting the entire PageUptodate, which will 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.
> - 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@xxxxxxxxxx>
> Reported-by: Jim Meyering <jim@xxxxxxxxxxxx>
> Reported-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Mingming Cao <cmm@xxxxxxxxxx>
> ---
> Changlog since v2:
> - Removed clear_buffer_dirty() call
> - Consolidated error handling for pages and buffer heads
> - Loop over BHs in a page even for page size == block size, so
> we emit the correct error for such a case.
>
> Changlog since v1:
> - Added commit message text about setting AS_EIO for the
> page on error.
> - Continue to loop over all BHs in a page and emit unique
> errors for each of them.
> ---
> fs/ext4/page-io.c | 39 +++++++++++----------------------------
> 1 files changed, 11 insertions(+), 28 deletions(-)
>
> diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
> index b6dbd05..7bb8f76 100644
> --- a/fs/ext4/page-io.c
> +++ b/fs/ext4/page-io.c
> @@ -203,46 +203,29 @@ static void ext4_end_bio(struct bio *bio, int error)
> 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);
> -
> - }
> - 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 <= io_end_offset))
> + buffer_io_error(bh);
> +
> 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;
> --
> 1.7.3.1
I'm concerned that we've reached -rc7, with Linus planning on 2.6.39
release next week, but Curt's fix above to the mblk_io corruption bug
seems to have fallen through the cracks.
I've been including it in all my testing over the last two weeks: it
works fine - and because of my own tmpfs bug, I even got to see its
error messages :) Adding in the patch is easy enough for me,
but surely we don't want others to stumble into this bug.
Thanks,
Hugh
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