On Tue, Mar 17, 2009 at 06:33:54PM +0100, Jan Kara wrote:
> Assume the following situation:
> Filesystem with blocksize < pagesize - suppose blocksize = 1024,
> pagesize = 4096. File 'f' has first four blocks already allocated.
> (line with "state:" contains the state of buffers in the page - m = mapped,
> u = uptodate, d = dirty)
>
> process 1: process 2:
>
> write to 'f' bytes 0 - 1024
> state: |mud,-,-,-|, page dirty
> write to 'f' bytes 1024 - 4096:
> __block_prepare_write() maps blocks
> state: |mud,m,m,m|, page dirty
> we fail to copy data -> copied = 0
> block_write_end() does nothing
> page gets unlocked
> writepage() is called on the page
> block_write_full_page() writes buffers with garbage
>
> This patch fixes the problem by skipping !uptodate buffers in
> block_write_full_page().
>
> CC: Nick Piggin <npiggin@xxxxxxx>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> fs/buffer.c | 7 ++++++-
> 1 files changed, 6 insertions(+), 1 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 9f69741..22c0144 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1774,7 +1774,12 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
> } while (bh != head);
>
> do {
> - if (!buffer_mapped(bh))
> + /*
> + * Parallel write could have already mapped the buffers but
> + * it then had to restart before copying in new data. We
> + * must avoid writing garbage so just skip the buffer.
> + */
> + if (!buffer_mapped(bh) || !buffer_uptodate(bh))
> continue;
I don't quite see how this can happen. Further down in this loop,
we do a test_clear_buffer_dirty(), which should exclude this I
think? And marking the buffer dirty if it is not uptodate should
be a bug.
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
