fs: fix data-loss on error

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.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index 09bb80c479d8..9ece6c2086d0 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1813,7 +1813,9 @@ static int __block_prepare_write(struct inode *inode, struct page *page,
                                 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) {