Unionfs: prevent multiple writers to lower_page

Without this patch, the LTP fs test "rwtest04" triggers a
BUG_ON(PageWriteback(page)) in fs/buffer.c:1706.

CC: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>

diff --git a/fs/unionfs/mmap.c b/fs/unionfs/mmap.c
index bfd2cadfdd0f7f384a80d07d56540020ba5671f4..9553dac4996b4c258057ab3d211d92cbc9a63812 100644 (file)
--- a/fs/unionfs/mmap.c
+++ b/fs/unionfs/mmap.c
@@ -104,6 +104,7 @@ static int unionfs_writepage(struct page *page, struct writeback_control *wbc)
 
        BUG_ON(!lower_mapping->a_ops->writepage);
        clear_page_dirty_for_io(lower_page); /* emulate VFS behavior */
+       wait_on_page_writeback(lower_page); /* prevent multiple writers */
        err = lower_mapping->a_ops->writepage(lower_page, wbc);
        wbc->for_writepages = saved_for_writepages; /* restore value */
        if (err < 0)