ext4: Make ext4_bio_writepage() handle unprepared buffers

So far ext4_bio_writepage() unconditionally cleared dirty bit on all
buffers underlying the page. That implicitely assumes we can write all
buffers. So far that is true because callers call into
ext4_bio_writepage() make sure all buffers in the page are mapped but:

a) it's a data corruption bug waiting to happen
b) in data=ordered mode when blocksize < pagesize we do need to write
   pages that may have only some of dirty buffers mapped.

So change ext4_bio_writepage() to skip buffers that cannot be written without
clearing their dirty bit.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 3fb385c..0290bf8 100644 (file)
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -350,14 +350,6 @@ static int io_submit_add_bh(struct ext4_io_submit *io,
                unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
        }
 
-       if (!buffer_mapped(bh) || buffer_delay(bh)) {
-               if (!buffer_mapped(bh))
-                       clear_buffer_dirty(bh);
-               if (io->io_bio)
-                       ext4_io_submit(io);
-               return 0;
-       }
-
        if (io->io_bio && bh->b_blocknr != io->io_next_block) {
 submit_and_retry:
                ext4_io_submit(io);
@@ -436,6 +428,15 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
                        set_buffer_uptodate(bh);
                        continue;
                }
+               if (!buffer_dirty(bh) || buffer_delay(bh) ||
+                   !buffer_mapped(bh) || buffer_unwritten(bh)) {
+                       /* A hole? We can safely clear the dirty bit */
+                       if (!buffer_mapped(bh))
+                               clear_buffer_dirty(bh);
+                       if (io->io_bio)
+                               ext4_io_submit(io);
+                       continue;
+               }
                ret = io_submit_add_bh(io, io_page, inode, wbc, bh);
                if (ret) {
                        /*