New buffers against uptodate pages are simply be marked uptodate, while the
buffer_new bit remains set. This causes error-case code to zero out parts
of those buffers because it thinks they contain stale data: wrong, they
are actually uptodate so this is a data loss situation.

Fix this by actually clearning buffer_new and marking the buffer dirty. It
makes sense to always clear buffer_new before setting a buffer uptodate.

Cc: Linux Memory Management <[EMAIL PROTECTED]>
Cc: Linux Filesystems <linux-fsdevel@vger.kernel.org>
Signed-off-by: Nick Piggin <[EMAIL PROTECTED]>

 fs/buffer.c |    2 ++
 1 file changed, 2 insertions(+)

Index: linux-2.6/fs/buffer.c
===================================================================
--- linux-2.6.orig/fs/buffer.c
+++ linux-2.6/fs/buffer.c
@@ -1816,7 +1816,9 @@ static int __block_prepare_write(struct 
                                unmap_underlying_metadata(bh->b_bdev,
                                                        bh->b_blocknr);
                                if (PageUptodate(page)) {
+                                       clear_buffer_new(bh);
                                        set_buffer_uptodate(bh);
+                                       mark_buffer_dirty(bh);
                                        continue;
                                }
                                if (block_end > to || block_start < from) {

-- 

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