From 3d08bcc887a1c8d12be8d81f747ffa2e8a44b67b Mon Sep 17 00:00:00 2001
From: "Darrick J. Wong" <djwong@us.ibm.com>
Date: Fri, 27 May 2011 12:23:34 -0700
Subject: [PATCH] mm: Wait for writeback when grabbing pages to begin a write

When grabbing a page for a buffered IO write, the mm should wait for writeback
on the page to complete so that the page does not become writable during the IO
operation.  This change is needed to provide page stability during writes for
all filesystems.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 mm/filemap.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index bcdc393b6580..dac95a24deac 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2327,7 +2327,7 @@ struct page *grab_cache_page_write_begin(struct address_space *mapping,
 repeat:
 	page = find_lock_page(mapping, index);
 	if (page)
-		return page;
+		goto found;
 
 	page = __page_cache_alloc(mapping_gfp_mask(mapping) & ~gfp_notmask);
 	if (!page)
@@ -2340,6 +2340,8 @@ repeat:
 			goto repeat;
 		return NULL;
 	}
+found:
+	wait_on_page_writeback(page);
 	return page;
 }
 EXPORT_SYMBOL(grab_cache_page_write_begin);
-- 
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