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>

1 files changed, 9 insertions, 2 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 54e968650855..876bc595d0f8 100644
--- a/mm/filemap.c
+++ b/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);