linux-kernel - [176/200] NFS: Fix another nfs_wb

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Message-Id: <20100701174301.396919016@clark.site>
Date:	Thu, 01 Jul 2010 10:44:26 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Trond Myklebust <Trond.Myklebust@...app.com>
Subject: [176/200] NFS: Fix another nfs_wb_page() deadlock

2.6.34-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Trond Myklebust <Trond.Myklebust@...app.com>

commit 0522f6adedd2736cbca3c0e16ca51df668993eee upstream.

J.R. Okajima reports that the call to sync_inode() in nfs_wb_page() can
deadlock with other writeback flush calls. It boils down to the fact
that we cannot ever call writeback_single_inode() while holding a page
lock (even if we do set nr_to_write to zero) since another process may
already be waiting in the call to do_writepages(), and so will deny us
the I_SYNC lock.

Signed-off-by: Trond Myklebust <Trond.Myklebust@...app.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 fs/nfs/write.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1518,14 +1518,17 @@ int nfs_wb_page(struct inode *inode, str
 	};
 	int ret;
 
-	while(PagePrivate(page)) {
+	for (;;) {
 		wait_on_page_writeback(page);
 		if (clear_page_dirty_for_io(page)) {
 			ret = nfs_writepage_locked(page, &wbc);
 			if (ret < 0)
 				goto out_error;
+			continue;
 		}
-		ret = sync_inode(inode, &wbc);
+		if (!PagePrivate(page))
+			break;
+		ret = nfs_commit_inode(inode, FLUSH_SYNC);
 		if (ret < 0)
 			goto out_error;
 	}


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