ceph: writepage grabs and releases inode

Fixes a deadlock that is triggered due to kswapd,
while the page was locked and the iput couldn't tear
down the address space.

Signed-off-by: Yehuda Sadeh <yehuda@hq.newdream.net>
diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index bf53581..d0cdceb 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -448,8 +448,13 @@
 
 static int ceph_writepage(struct page *page, struct writeback_control *wbc)
 {
-	int err = writepage_nounlock(page, wbc);
+	int err;
+	struct inode *inode = page->mapping->host;
+	BUG_ON(!inode);
+	igrab(inode);
+	err = writepage_nounlock(page, wbc);
 	unlock_page(page);
+	iput(inode);
 	return err;
 }