VFS: fix dio write returning EIO when try_to_release_page fails

Dio write returns EIO when try_to_release_page fails because bh is
still referenced.

The patch

    commit 3f31fddfa26b7594b44ff2b34f9a04ba409e0f91
    Author: Mingming Cao <cmm@us.ibm.com>
    Date:   Fri Jul 25 01:46:22 2008 -0700

        jbd: fix race between free buffer and commit transaction

was merged into 2.6.27-rc1, but I noticed that this patch is not enough
to fix the race.

I did fsstress test heavily to 2.6.27-rc1, and found that dio write still
sometimes got EIO through this test.

The patch above fixed race between freeing buffer(dio) and committing
transaction(jbd) but I discovered that there is another race, freeing
buffer(dio) and ext3/4_ordered_writepage.

: background_writeout()
     ->write_cache_pages()
       ->ext3_ordered_writepage()
     	   walk_page_buffers() -> take a bh ref
 	   block_write_full_page() -> unlock_page
		: <- end_page_writeback
                : <- race! (dio write->try_to_release_page fails)
      	   walk_page_buffers() ->release a bh ref

ext3_ordered_writepage holds bh ref and does unlock_page remaining
taking a bh ref, so this causes the race and failure of
try_to_release_page.

To fix this race, I used the approach of falling back to buffered
writes if try_to_release_page() fails on a page.

[akpm@linux-foundation.org: cleanups]
Signed-off-by: Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Mingming Cao <cmm@us.ibm.com>
Cc: Zach Brown <zach.brown@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/filemap.c

@@ -2129,13 +2129,20 @@ generic_file_direct_write(struct kiocb *iocb, const struct iovec *iov,
 	 * After a write we want buffered reads to be sure to go to disk to get
 	 * the new data.  We invalidate clean cached page from the region we're
 	 * about to write.  We do this *before* the write so that we can return
-	 * -EIO without clobbering -EIOCBQUEUED from ->direct_IO().
+	 * without clobbering -EIOCBQUEUED from ->direct_IO().
 	 */
 	if (mapping->nrpages) {
 		written = invalidate_inode_pages2_range(mapping,
 					pos >> PAGE_CACHE_SHIFT, end);
-		if (written)
+		/*
+		 * If a page can not be invalidated, return 0 to fall back
+		 * to buffered write.
+		 */
+		if (written) {
+			if (written == -EBUSY)
+				return 0;
 			goto out;
+		}
 	}
 
 	written = mapping->a_ops->direct_IO(WRITE, iocb, iov, pos, *nr_segs);

mm/truncate.c

@@ -380,7 +380,7 @@ static int do_launder_page(struct address_space *mapping, struct page *page)
  * Any pages which are found to be mapped into pagetables are unmapped prior to
  * invalidation.
  *
- * Returns -EIO if any pages could not be invalidated.
+ * Returns -EBUSY if any pages could not be invalidated.
  */
 int invalidate_inode_pages2_range(struct address_space *mapping,
 				  pgoff_t start, pgoff_t end)
@@ -440,7 +440,7 @@ int invalidate_inode_pages2_range(struct address_space *mapping,
 			ret2 = do_launder_page(mapping, page);
 			if (ret2 == 0) {
 				if (!invalidate_complete_page2(mapping, page))
-					ret2 = -EIO;
+					ret2 = -EBUSY;
 			}
 			if (ret2 < 0)
 				ret = ret2;