Commit 6ccfa806 authored Sep 02, 2008 by Hisashi Hifumi Committed by Linus Torvalds Sep 02, 2008

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 3f31fddf
    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>

parent 344c790e

mm/filemap.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -2129,14 +2129,21 @@ 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

+2 −2

Original line number	Diff line number	Diff line
		@@ -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;