Messages in this thread Patch in this message |  | | | From | Jan Kara <> | | Subject | [PATCH 3/4] fs: Avoid data corruption with blocksize < pagesize | | Date | Tue, 17 Mar 2009 18:33:54 +0100 |
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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@suse.de> Signed-off-by: Jan Kara <jack@suse.cz> --- 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; /* * If it's a fully non-blocking write attempt and we cannot -- 1.6.0.2
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