From: Erez Zadok <ezk@cs.sunysb.edu>
Date: Sun, 25 Nov 2007 19:51:56 +0000 (-0500)
Subject: Unionfs: prevent multiple writers to lower_page
X-Git-Url: https://git.fsl.cs.sunysb.edu/?a=commitdiff_plain;h=6355ac7cb3f0f107c5a21a3529ce3fada244e383;p=unionfs-3.8.y.git

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 623a91362ff..ea5ef3d5901 100644
--- a/fs/unionfs/mmap.c
+++ b/fs/unionfs/mmap.c
@@ -73,6 +73,7 @@ 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);
 	if (err < 0)
 		goto out_release;