linux-kernel - [PATCH 14/16] Unionfs: prevent multiple writers to lower

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Message-Id: <11960954592000-git-send-email-ezk@cs.sunysb.edu>
Date:	Mon, 26 Nov 2007 11:44:11 -0500
From:	Erez Zadok <ezk@...sunysb.edu>
To:	akpm@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	viro@....linux.org.uk, hch@...radead.org,
	Erez Zadok <ezk@...sunysb.edu>, Hugh Dickins <hugh@...itas.com>
Subject: [PATCH 14/16] 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@...itas.com>

Signed-off-by: Erez Zadok <ezk@...sunysb.edu>
---
 fs/unionfs/mmap.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/fs/unionfs/mmap.c b/fs/unionfs/mmap.c
index 623a913..ea5ef3d 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;
-- 
1.5.2.2

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